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[1]  arXiv:1412.5582 [pdf]
Title: Infrared Spectra and Chemical Abundance of Methyl Propionate in Icy Astrochemical Conditions
Comments: 14 pages, 3 figures, accepted in MNRAS for publication
Subjects: Astrophysics of Galaxies (astro-ph.GA); Chemical Physics (physics.chem-ph)

We carried out an experiment in order to obtain the InfraRed (IR) spectra of methyl propionate (CH3CH2COOCH3) in astrochemical conditions and present the IR spectra for future identification of this molecule in the InterStellar Medium (ISM). The experimental IR spectrum is compared with the theoretical spectrum and an attempt was made to assign the observed peak positions to their corresponding molecular vibrations in condensed phase. Moreover, our calculations suggest that methyl propionate must be synthesized efficiently within the complex chemical network of the ISM and therefore be present in cold dust grains, awaiting identification.

[2]  arXiv:1412.5584 [pdf, ps, other]
Title: The stellar mass - halo mass relation from galaxy clustering in VUDS: a high star formation efficiency at z~3
Comments: 4 pages, 2 figures, submitted to A&A
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

The relation between the galaxy stellar mass M_star and the dark matter halo mass M_h gives important information on the efficiency in forming stars and assembling stellar mass in galaxies. We present the stellar mass to halo mass ratio (SMHR) measurements at redshifts 2<z<5, obtained from the VIMOS Ultra Deep Survey. We use halo occupation distribution (HOD) modelling of clustering measurements on ~3000 galaxies with spectroscopic redshifts to derive the dark matter halo mass M_h, and SED fitting over a large set of multi-wavelength data to derive the stellar mass M_star and compute the SMHR=M_star/M_h. We find that the SMHR ranges from 1% to 2.5% for galaxies with M_star=1.3x10^9 M_sun to M_star=7.4x10^9 M_sun in DM halos with M_h=1.3x10^{11} M_sun} to M_h=3x10^{11} M_sun. We derive the integrated star formation efficiency (ISFE) of these galaxies and find that the star formation efficiency is a moderate 6-9% for lower mass galaxies while it is relatively high at 16% for galaxies with the median stellar mass of the sample ~7x10^9 M_sun. The lower ISFE at lower masses may indicate that some efficient means of suppressing star formation is at work (like SNe feedback), while the high ISFE for the average galaxy at z~3 is indicating that these galaxies are efficiently building-up their stellar mass at a key epoch in the mass assembly process. We further infer that the average mass galaxy at z~3 will start experiencing star formation quenching within a few hundred millions years.

[3]  arXiv:1412.5588 [pdf, ps, other]
Title: The interplay of disk wind and dynamical ejecta in the aftermath of neutron star - black hole mergers
Comments: Submitted to MNRAS, comments welcome
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR); General Relativity and Quantum Cosmology (gr-qc); Nuclear Theory (nucl-th)

We explore the evolution of the different ejecta components generated during the merger of a neutron star (NS) and a black hole (BH). Our focus is the interplay between material ejected dynamically during the merger, and the wind launched on a viscous timescale by the remnant accretion disk. These components are expected to contribute to an electromagnetic transient and to produce r-process elements, each with a different signature when considered separately. Here we introduce a two-step approach to investigate their combined evolution, using two- and three-dimensional hydrodynamic simulations. Starting from the output of a merger simulation, we identify each component in the initial condition based on its phase space distribution, and evolve the accretion disk in axisymmetry. The wind blown from this disk is injected into a three-dimensional computational domain where the dynamical ejecta is evolved. We find that the wind can suppresses fallback accretion on timescales longer than ~100 ms. Due to self-similar viscous evolution, the disk accretion at late times nevertheless approaches a power-law time dependence $\propto t^{-2.2}$. This can power some late-time GRB engine activity, although the available energy is significantly less than in traditional fallback models. Inclusion of radioactive heating due to the r-process does not significantly affect the fallback accretion rate or the disk wind. We do not find any significant modification to the wind properties at large radius due to interaction with the dynamical ejecta. This is a consequence of the different expansion velocities of the two components.

[4]  arXiv:1412.5592 [pdf, other]
Title: Sagittarius A* Rivaled the Sun in the Ancient X-ray Sky
Comments: Submitted. Comments welcome. Both authors contributed equally to this research project. Correspondence and requests for materials should be addressed to Pau.Amaro-Seoane@aei.mpg.de
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)

Sagittarius A*, lying the Galactic Center $8$ kpc from Earth, hosts the closest supermassive black hole known to us. It is now inactive, but there are evidences indicating that about six million years ago it underwent a powerful outburst where the luminosity could have approached the Eddington limit. Motivated by the fact that in extragalaxies the supermassive black holes with similar masses and near-Eddington luminosities are usually strong X-ray emitters, we calculate here the X-ray luminosity of Sagittarius A*, assuming that the outburst was due to accretion of gas or tidal disruption of stars, both scenarios having been considered to trigger the previous outburst. We show that in both cases Sagittarius A* could precipitate on Earth an X-ray ($h\nu>2$ keV) irradiance comparable to that from the current quiescent sun. The irradiance in harder energy band $20~{\rm keV}<h\nu<100~{\rm keV}$, however, surpasses that from an X-class solar flare, and the irradiation timescale is also much longer, ranging from weeks to $10^5$ years depending on the outburst scenario. This level of radiation would disturb the ozone and ionosphere around the ancient earth, and affect the abundance of organic molecules in dense interstellar environments around the solar neighbourhood, but these prospects have not been adequately explored so far. Our results indicate that the activity of supermassive black hole and the origin and evolution of life may be more closely linked than previously has been thought.

[5]  arXiv:1412.5593 [pdf, other]
Title: Deconstructing Thermal Sunyaev-Zel'dovich - Gravitational Lensing Cross-Correlations: Implications for the Intracluster Medium
Authors: N. Battaglia (Princeton), J. C. Hill (Columbia), N. Murray (CITA)
Comments: 16 pages, 8 Figures, submitted to ApJ, comments welcome
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Recent first detections of the cross-correlation of the thermal Sunyaev-Zel'dovich (tSZ) signal in Planck cosmic microwave background (CMB) temperature maps with gravitational lensing maps inferred from the Planck CMB data and the CFHTLenS galaxy survey provide new probes of the relationship between baryons and dark matter. Using cosmological hydrodynamics simulations, we show that these cross-correlation signals are dominated by contributions from hot gas in the intracluster medium (ICM), rather than diffuse, unbound gas located beyond the virial radius (the "missing baryons"). Thus, these cross-correlations offer a tool with which to study the ICM over a wide range of halo masses and redshifts. In particular, we show that the tSZ - CMB lensing cross-correlation is more sensitive to gas in lower-mass, higher-redshift halos and gas at larger cluster-centric radii than the tSZ - galaxy lensing cross-correlation. Combining these measurements with primary CMB data will constrain feedback models through their signatures in the ICM pressure profile. We forecast the ability of ongoing and future experiments to constrain such ICM parameters, including the mean amplitude of the pressure - mass relation, the redshift evolution of this amplitude, and the mean outer logarithmic slope of the pressure profile. The results are promising, with $\approx 5-20$% precision constraints achievable with upcoming experiments, even after marginalizing over cosmological parameters.

[6]  arXiv:1412.5598 [pdf, other]
Title: Five steps in the evolution from protoplanetary to debris disk
Comments: 23 pages. Accepted for publication in Astrophysics and Space Science
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

The protoplanetary disks of Herbig Ae stars eventually dissipate leaving a tenuous debris disk comprised of planetesimals and dust, as well as possibly gas and planets. This paper uses the properties of 10-20Myr A star debris disks to consider the protoplanetary to debris disk transition. The physical distinction between these two classes is argued to rest on the presence of primordial gas in sufficient quantities to dominate the motion of small dust grains (not the secondary nature of the dust or its level of stirring). This motivates an observational classification based on the dust spectrum, empirically defined so that A star debris disks require fractional excesses <3 at 12um and <2000 at 70um. We also propose a hypothesis to test, that the main sequence planet/planetesimal structures are already in place (but obscured) during the protoplanetary disk phase. This may be only weakly true if planetary architectures change until frozen during disk dispersal, or completely false if planets and planetesimals form during disk dispersal. Five steps in the transition are discussed: (i) carving an inner hole to form a transition disk; (ii) depletion of mm-sized dust in outer disk, noting the importance of determining whether this mass ends up in planetesimals or is collisionally depleted; (iii) final clearing of inner regions, noting that many mechanisms replenish moderate hot dust levels at later phases, and likely also operate in protoplanetary disks; (iv) disappearence of gas, noting recent discoveries of primordial and secondary gas in debris disks that highlight our ignorance and its impending enlightenment by ALMA; (v) formation of ring-like planetesimal structures, noting these are shaped by interactions with planets, and that the location of planetesimals in protoplanetary disks may be unrelated to the dust concentrations therein that are set by gas interactions.

[7]  arXiv:1412.5602 [pdf, ps, other]
Title: Radio AGN in spiral galaxies
Comments: Submitted to MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Radio AGN in the nearby Universe are more likely to be found in galaxies with early-type morphology, the detection rate in spiral or late-type galaxies (LTGs) being around an order of magnitude lower. We combine the mJy Imaging VLBA Exploration at 20cm (mJIVE-20) survey with the Sloan Digital Sky Survey (SDSS), to study the relatively rare population of AGN in LTGs that have nuclear radio luminosities similar to that in their early-type counterparts. The LTG AGN population is preferentially hosted by galaxies that have high stellar masses (M* > 10^10.8 MSun), red colours and low star-formation rates, with little dependence on the detailed morphology or local environment of the host LTG. The merger fraction in the LTG AGN is around 4 times higher than that in the general LTG population, indicating that merging is an important trigger for radio AGN in these systems. The red colours of our systems extend recent work which indicates that merger-triggered AGN in the nearby Universe appear after the peak of the associated starburst, implying that they do not strongly regulate star formation. Finally, we find that in systems where parsec-scale jets are clearly observed in our VLBI images, the jets are perpendicular to the major axis of the galaxy, indicating alignment between the accretion disc and the host galaxy stellar disc.

[8]  arXiv:1412.5607 [pdf, other]
Title: Cosmic Reionization On Computers III. The Clumping Factor
Comments: 8 pages, 10 figure, submitted to ApJ
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We use fully self-consistent numerical simulations of cosmic reionization, completed under the Cosmic Reionization On Computers (CROC) project, to explore how well the recombinations in the ionized IGM can be quantified by the effective "clumping factor". The density distribution in the simulations (and, presumably, in a real universe) is highly inhomogeneous and more-or-less smoothly varying in space. However, even in highly complex and dynamic environments the concept of the IGM remains reasonably well-defined; the largest ambiguity comes from the unvirialized regions around galaxies that are over-ionized by the local enhancement in the radiation field ("proximity zones"). That ambiguity precludes computing the IGM clumping factor to better than about 20\%. We also discuss a "local clumping factor", defined over a particular spatial scale, and quantify its scatter on a given scale and its variation as a function of scale.

[9]  arXiv:1412.5623 [pdf, other]
Title: Atmospheric Response to of an Active Region to new Small Flux Emergence
Comments: 20 pages, 15 figures. Accepted by the Solar Physics journal
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We investigate the atmospheric response to a small emerging flux region (EFR) that occurred in the positive polarity of Active Region 11236 on 23 \,-\ 24 June 2011. Data from the \textit{Solar Dynamics Observatory's Atmopheric Imaging Assembly} (AIA), the \textit{Helioseismic and Magnetic Imager} (HMI) and Hinode's \textit{EUV imaging spectrometer} (EIS) are used to determine the atmospheric response to new flux emerging into a pre-existing active region.
Brightenings are seen forming in the upper photosphere, chromosphere, and corona over the EFR's location whilst flux cancellation is observed in the photosphere. The impact of the flux emergence is far reaching, with new large-scale coronal loops forming up to 43 Mm from the EFR and coronal upflow enhancements of approximately 10 km s$^{-1}$ on the north side of the EFR. Jets are seen forming in the chromosphere and the corona over the emerging serpentine field. This is the first time that coronal jets have been seen over the serpentine field.

[10]  arXiv:1412.5630 [pdf, other]
Title: Short vs. Long Gamma-Ray Bursts: A Comprehensive Study of Energetics and Prompt Gamma-Ray Correlations
Authors: Amir Shahmoradi (UT Austin), Robert J. Nemiroff (MTU)
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Data Analysis, Statistics and Probability (physics.data-an); Instrumentation and Detectors (physics.ins-det)

We present the results of a comprehensive study of the luminosity function, energetics, prompt gamma-ray correlations, and classification methodology of short-hard and long-soft GRBs (SGRBs & LGRBs), based on observational data in the largest catalog of GRBs available to this date: BATSE catalog of 2130 GRBs. We find that: 1. The least-biased classification method of GRBs into short and long, solely based on prompt--emission properties appears to be the ratio of the observed spectral peak energy to the observed duration (R=Epk/T90) with the dividing line at R=50[erg/s]. 2. Once data is carefully corrected for the effects of the detection threshold of gamma-ray instruments, the population distribution of SGRBs and LGRBs can be individually well described as multivariate log-normal distribution in the 4-dimensional space of the isotropic peak gamma-ray luminosity, total isotropic gamma-ray emission, the intrinsic spectral peak energy, and the intrinsic duration. 3. Relatively large fractions of SGRBs and LGRBs with moderate-to-low spectral peak energies have been missed by BATSE detectors. 4. Relatively strong and significant intrinsic hardness-brightness and duration-brightness correlations likely exist in both populations of SGRBs and LGRBs, once data is corrected for selection effects. The strengths of these correlations are very similar in both populations, implying similar mechanisms at work in both GRB classes, leading to the emergence of these prompt gamma-ray correlations.

[11]  arXiv:1412.5638 [pdf, other]
Title: CAFÉ-BEANS: An exhaustive hunt for high-mass binaries
Comments: 6 pages. To appear in Highlights of Spanish Astrophysics VIII, Proceedings of the XI Scientific Meeting of the Spanish Astronomical Society held on September 8 - 12, 2014, in Teruel, Spain. A. J. Cenarro, F. Figueras, C. Hern\'andez-Monteagudo, J. Trujillo, and L. Valdivielso (eds.)
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

CAF\'E-BEANS is an on-going survey running on the 2.2 m telescope at Calar Alto. For more than two years, CAF\'E-BEANS has been collecting high-resolution spectra of early-type stars with the aim of detecting and characterising spectroscopic binaries. The main goal of this project is a thorough characterisation of multiplicity in high-mass stars by detecting all spectroscopic and visual binaries in a large sample of Galactic O-type stars, and solving their orbits. Our final objective is eliminating all biases in the high-mass-star IMF created by undetected binaries.

[12]  arXiv:1412.5639 [pdf, ps, other]
Title: Particles under radiation thrust in Schwarzschild space-time from a flux perpendicular to the equatorial plane
Comments: 14 pages, 10 figures
Journal-ref: MNRAS, 2015, vol. 446, p. 2317-2329
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc)

Motivated by the picture of a thin accretion disc around a black hole, radiating mainly in the direction perpendicular to its plane, we study the motion of test particles interacting with a test geodesic radiation flux originating in the equatorial plane of a Schwarzschild space-time and propagating initially in the perpendicular direction. We assume that the interaction with the test particles is modelled by an effective term corresponding to the Thomson-type interaction which governs the Poynting-Robertson effect. After approximating the individual photon trajectories adequately, we solve the continuity equation approximately in order to find a consistent flux density with a certain plausible prescribed equatorial profile. The combined effects of gravity and radiation are illustrated in several typical figures which confirm that the particles are generically strongly influenced by the flux. In particular, they are both collimated and accelerated in the direction perpendicular to the disc, but this acceleration is not enough to explain highly relativistic outflows emanating from some black hole-disc sources. The model can however be improved in a number of ways before posing further questions which are summarized in concluding remarks.

[13]  arXiv:1412.5643 [pdf, ps, other]
Title: Radio investigation of Ultra-Luminous X-ray Sources in the SKA Era
Authors: Anna Wolter (1), Anthony P. Rushton (2 and 3), Mar Mezcua (4), David Cseh (5), Fabio Pintore (6), Isabella Prandoni (7), Zsolt Paragi (8), Luca Zampieri (9) ((1) INAF-Osservatorio Astronomico di Brera, Milano (2) University of Oxford, (3) University of Southampton, (4) Instituto de Astrofisica de Canarias, (5) Radboud University, Nijmegen, (6) Università degli Studi di Cagliari, (7) INAF-IRA Bologna, (8) JIVE, Dwingeloo, (9) INAF-Osservatorio Astronomico di Padova)
Comments: 13 pages, 2 figures; to appear as part of 'Continuum Science' in Proceedings 'Advancing Astrophysics with the SKA (AASKA14)'
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Astrophysics of Galaxies (astro-ph.GA)

A puzzling class of exotic objects, which have been known about for more than 30 years, is reaching a new era of understanding. We have discovered hundreds of Ultra Luminous X-ray sources (ULXs) - non-nuclear sources with X-ray luminosity in excess of the Eddington luminosity for "normal" size stellar Black Holes (BH) - and we are making progresses towards understanding their emission mechanisms. The current explanations imply either a peculiar state of accretion onto a stellar size BH or the presence of an intermediate mass BH, the long-sought link between stellar and supermassive BHs. Both models might co-exist and therefore studying this class of object will give insight into the realm of accretion in a variety of environments and at the same time find look-alikes of the primordial seed BHs that are thought to be at the origin of todays supermassive BHs at the centre of galaxies. The radio band has been exploited only scantily due to the relative faint fluxes of the sources, but we know a number of interesting sources exhibiting both extended emission (like bubbles and possibly jets) and cores, as well as observed transient behaviour. The new eras of the SKA will lead us to a major improvement of our insight of the extreme accretion within ULXs. We will both investigate in detail known sources and research new and fainter ones. When we have reached a thorough understanding of radio emission in ULX we could also use the SKA as a discovery instrument for new ULX candidates. The new array will give an enormous space to discovery: sources like the ones currently known will be detected in a snapshot up to 50 Mpc instead of at 5 Mpc with long, pointed observations.

[14]  arXiv:1412.5649 [pdf, other]
Title: The Rich Are Different: Evidence from the RAVE Survey for Stellar Radial Migration
Comments: submitted to MNRAS, 11 pages, 11 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Using the RAdial Velocity Experiment fourth data release (RAVE DR4), and a new metallicity calibration that will be also taken into account in the future RAVE DR5, we investigate the existence and the properties of super-solar metallicity stars ([M/H] > +0.1 dex) in the sample, and in particular in the Solar neighbourhood. We find that RAVE is rich in super-solar metallicity stars, and that the local metallicity distribution function declines remarkably slowly up to +0.4 dex. Our results show that the kinematics and height distributions of the super-solar metallicity stars are identical to those of the [M/H] < 0 thin-disc giants that we presume were locally manufactured. The eccentricities of the super-solar metallicity stars indicate that half of them are on a roughly circular orbit (e < 0.15), so under the assumption that the metallicity of the interstellar medium at a given radius never decreases with time, they must have increased their angular momenta by scattering at corotation resonances of spiral arms from regions far inside the Solar annulus. The likelihood that a star will migrate radially does not seem to decrease significantly with increasing amplitude of vertical oscillations within range of oscillation amplitudes encountered in the disc.

[15]  arXiv:1412.5650 [pdf, ps, other]
Title: Approximating light rays in the Schwarzschild field
Authors: Oldrich Semerak
Comments: 13 pages, 6 figures; accepted to ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc)

A short formula is suggested which approximates photon trajectories in the Schwarzschild field better than other simple prescriptions from the literature. We compare it with various "low-order competitors", namely with those following from exact formulas for small $M$, with one of the results based on pseudo-Newtonian potentials, with a suitably adjusted hyperbola, and with the effective and often employed approximation by Beloborodov. Our main concern is the shape of the photon trajectories at finite radii, yet asymptotic behaviour is also discussed, important for lensing. An example is attached indicating that the newly suggested approximation is usable--and very accurate--for practical solving of the ray-deflection exercise.

[16]  arXiv:1412.5653 [pdf, other]
Title: Measuring the speed of light with Baryon Acoustic Oscillations
Comments: 5 pages, 3 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

In this letter we describe a new method to use Baryon Acoustic Oscillations (BAO) to derive a constraint on the possible variation of the speed of light. The method relies on the fact that there is a simple relation between the angular diameter distance $(D_{A})$ maximum and the Hubble function $(H)$ evaluated at the same maximum-condition redshift, which includes speed of light $c$. We note the close analogy of the BAO probe with a laboratory experiment: here we have $D_{A}$ which plays the role of a standard (cosmological) ruler, and $H^{-1}$, with the dimension of time, as a (cosmological) clock. We evaluate if current or future missions such as Euclid can be sensitive enough to detect any variation of $c$.

[17]  arXiv:1412.5658 [pdf, ps, other]
Title: The Emission Nebula Sh 2-174: A Radio Investigation of the Surrounding Region
Comments: 40 pages, 10 figures. Accepted for publication in ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Sh 2-174 is believed to be either a planetary nebula (PN) or ionized, ambient interstellar medium (ISM). We present in this paper 1420 MHz polarization, 1420 MHz total intensity (Stokes-I), and neutral hydrogen (HI) images of the region around Sh 2-174. The radio images address not only the nature of the object, but also the history of the relationship between Sh 2-174 and its surrounding environment. The HI images show that Sh 2-174 sits presently at the center of a 1.2 deg x 0.4 deg cloud. The Stokes-I image shows thermal emission peaks coincident with the R-band optical nebula, as well as low-surface-brightness emission from an ionized "halo" around Sh 2-174 and from an ionized "plateau" extending southeast from the cloud. The polarization images reveal Faraday-rotation structures along the projected trajectory of Sh 2-174, including a high-contrast structure with "arms" that run precisely along the eastern edge of the HI cloud and a wide central region which merges with the downstream edge of Sh 2-174. The high-contrast structure is consistent with an ionized tail which has both early-epoch (before Sh 2-174 entered the cloud) and present-epoch (after Sh 2-174 entered the cloud) components. Furthermore, our rotation-measure analysis indicates that the ISM magnetic field is deflected at the leading edge of Sh 2-174. The downstream tail and upstream field deflection point to a PN-ISM interaction. Our estimated space velocity for the host white dwarf (GD~561) demonstrates that Sh 2-174 entered the cloud approximately 27,000 yr ago, and gives a PN-ISM interaction timescale less than approximately 200,000 yr. We estimate an ambient magnetic field in the cloud of 11 +/- 3 microGauss.

[18]  arXiv:1412.5662 [pdf, other]
Title: Merging Binary Stars and the magnetic white dwarfs
Comments: 12 Pages, 6 figures, accepted for publication in the MNRAS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

A magnetic dynamo driven by differential rotation generated when stars merge can explain strong fields in certain classes of magnetic stars, including the high field magnetic white dwarfs (HFMWDs). In their case the site of the differential rotation has been variously proposed to be within a common envelope, the massive hot outer regions of a merged degenerate core or an accretion disc formed by a tidally disrupted companion that is subsequently incorporated into a degenerate core. We synthesize a population of binary systems to investigate the stellar merging hypothesis for observed single HFMWDs. Our calculations provide mass distribution and the fractions of white dwarfs that merge during a common envelope phase or as double degenerate systems in a post common envelope phase. We vary the common envelope efficiency parameter alpha and compare with observations. We find that this hypothesis can explain both the observed incidence of magnetism and the mass distribution of HFMWDs for a wide range of alpha. In this model, the majority of the HFMWDs are of the Carbon Oxygen type and merge within a common envelope. Less than about a quarter of a per cent of HFMWDs originate from double degenerate stars that merge after common envelope evolution and these populate the high-mass tail of the HFMWD mass distribution.

[19]  arXiv:1412.5664 [pdf, ps, other]
Title: The SKA view of cool-core clusters: evolution of radio mini-halos and AGN feedback
Comments: 17 pages, 5 figures. To appear as part of 'Continuum Science' in Proceedings of "Advancing Astrophysics with the SKA (AASKA14)", PoS(AASKA14)076
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA)

In about 70% of the population of relaxed, cool-core galaxy clusters, the brightest cluster galaxy (BCG) is radio loud, showing non-thermal radio jets and lobes ejected by the central active galactic nucleus (AGN). In recent years such relativistic plasma has been unambiguously shown to interact with the surrounding thermal intra-cluster medium (ICM) thanks to spectacular images where the lobe radio emission is observed to fill the cavities in the X-ray-emitting gas. This `radio feedback' phenomenon is widespread and is critical to understand the physics of the inner regions of galaxy clusters and the properties of the central BCG. At the same time, mechanically-powerful AGN are likely to drive turbulence in the central ICM which may also play a role for the origin of non-thermal emission on cluster-scales. Diffuse non-thermal emission has been observed in a number of cool-core clusters in the form of a radio mini-halo surrounding the radio-loud BCG on scales comparable to that of the cooling region. Large mini-halo samples are necessary to establish their origin and connection with the cluster thermal properties and dynamics, especially in light of future X-ray characterization of the cluster cores as it is expected by Athena-XIFU. We show that All-Sky reference survey at Band 2 with SKA1 at confusion limit (rms ~2 {\mu}Jy per beam) has the potential to detect up to ~620 mini-halos at redshift z<0.6, whereas Deep Tier reference surveys at Band 1/2 with SKA1 at sub-arcsec resolution (rms ~0.2 {\mu}Jy per beam) will allow a complete census of the radio-loud BCGs at any redshift down to a 1.4 GHz power of 10^{22} W/Hz. We further anticipate that SKA2 might detect up to ~1900 new mini-halos at redshift z<0.6 and characterize the radio-mode AGN feedback in every cluster and group up to redshift z ~1.7 (the highest-z where virialized clusters are currently detected).

[20]  arXiv:1412.5674 [pdf, ps, other]
Title: Characterizing K2 Planet Discoveries: A super-Earth transiting the bright K-dwarf HIP 116454
Comments: 16 pages, 8 figures. Accepted by ApJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)

We report the first planet discovery from the two-wheeled Kepler (K2) mission: HIP 116454 b. The host star HIP 116454 is a bright (V = 10.1, K = 8.0) K1-dwarf with high proper motion, and a parallax-based distance of 55.2 +/- 5.4 pc. Based on high-resolution optical spectroscopy, we find that the host star is metal-poor with [Fe/H] = -.16 +/- .18, and has a radius R = 0.716 +/- .0024 R_sun and mass M = .775 +/- .027 Msun. The star was observed by the Kepler spacecraft during its Two-Wheeled Concept Engineering Test in February 2014. During the 9 days of observations, K2 observed a single transit event. Using a new K2 photometric analysis technique we are able to correct small telescope drifts and recover the observed transit at high confidence, corresponding to a planetary radius of Rp = 2.53 +/- 0.18 Rearth. Radial velocity observations with the HARPS-N spectrograph reveal a 11.82 +/- 1.33 Mearth planet in a 9.1 day orbit, consistent with the transit depth, duration, and ephemeris. Follow-up photometric measurements from the MOST satellite confirm the transit observed in the K2 photometry and provide a refined ephemeris, making HIP 116454 b amenable for future follow-up observations of this latest addition to the growing population of transiting super-Earths around nearby, bright stars.

[21]  arXiv:1412.5677 [pdf, ps, other]
Title: The Astrophysics of Star Formation Across Cosmic Time at $\gtrsim$10 GHz with the Square Kilometer Array
Comments: 15 pages, 3 figures, to appear as part of 'Continuum Science' in Proceedings "Advancing Astrophysics with the Square Kilometre Array" PoS(AASKA14)085
Subjects: Astrophysics of Galaxies (astro-ph.GA)

In this chapter, we highlight a number of science investigations that are enabled by the inclusion of Band~5 ($4.6-13.8$ GHz) for SKA1-MID science operations, while focusing on the astrophysics of star formation over cosmic time. For studying the detailed astrophysics of star formation at high-redshift, surveys at frequencies $\gtrsim$10 GHz have the distinct advantage over traditional $\sim$1.4 GHz surveys as they are able to yield higher angular resolution imaging while probing higher rest frame frequencies of galaxies with increasing redshift, where emission of star-forming galaxies becomes dominated by thermal (free-free) radiation. In doing so, surveys carried out at $\gtrsim$10 GHz provide a robust, dust-unbiased measurement of the massive star formation rate by being highly sensitive to the number of ionizing photons that are produced. To access this powerful star formation rate diagnostic requires that Band~5 be available for SKA1-MID. We additionally present a detailed science case for frequency coverage extending up to 30 GHz during full SKA2 operations, as this allows for highly diverse science while additionally providing contiguous frequency coverage between the SKA and ALMA, which will likely be the two most powerful interferometers for the coming decades. To enable this synergy, it is crucial that the dish design of the SKA be flexible enough to include the possibility of being fit with receivers operating up to 30 GHz.

[22]  arXiv:1412.5678 [pdf, ps, other]
Title: Neutrino Constrains to the Diffuse Gamma-Ray Emission from Accretion Shocks
Comments: 12 pages, 1 figure. Comments welcome
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Accretion of gas during the large scale structure formation has been thought to give rise to shocks that can accelerate cosmic rays. This process then results in an isotropic extragalactic gamma-ray component that then contributes to the extragalactic gamma-ray background observed by the \emph{Fermi}-LAT. Unfortunately this gamma-ray background component has been difficult to constrain and thus presents an uncertain foreground to any attempts to extract potential dark matter signal. Recent IceCube neutrino detections have revealed a high-energy isotropic neutrino component which could be of an extragalactic origin. One possible source of these neutrino events can be found in cosmic-ray interactions. In general, neutrinos can be linked to gamma rays since cosmic-ray interactions produce neutral and charged pions where neutral pions decay into gamma rays, while charged pions decay to give neutrinos. By assuming that isotropic high-energy IceCube neutrinos are entirely produced by cosmic rays accelerated in accretion shocks during the process of structure formation, we obtain the strongest constraint to the gamma-ray emission from large scale structure formation (strong) shock and find that they can make at best ~50%, that is ~20% when attenuation at high-energies is taken into account, of the extragalactic gamma-ray background. Since typical objects where cosmic rays are accelerated in accretion shocks are galaxy clusters, observed high-energy neutrino fluxes can then be used to determine the gamma-ray emission of a dominant cluster type and thus probe the process of large scale structure formation.

[23]  arXiv:1412.5683 [pdf, ps, other]
Title: Time series photometry of the helium atmosphere pulsating white dwarf EC 04207-474
Comments: 9 pages, 3 figures, 6 tables
Journal-ref: MNRAS 431, pp520-527 (2013)
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We present the analysis of 71 hours of high quality time-series CCD photometry of the helium atmosphere pulsating white dwarf (DBV) EC 04207-4748 obtained using the facilities at Mt John University Observatory in New Zealand. The photometric data set consists of four week-long observing sessions covering the period March to November 2011. A Fourier analysis of the lightcurves yielded clear evidence of four independent eigenmodes in the star with the dominant mode having a period of 447 s. The lightcurve variations exhibit distinct nonsinusoidal shapes, which results in significant harmonics of the dominant frequency appearing in the Fourier transforms. These observed variations are interpreted in terms of nonlinear contributions from the energy flux transmission through the subsurface convection zone in the star. Our modelling of this mechanism, using the methods first introduced by Montgomery (2005), yields a time-averaged convective response time of tau_0 ~ 150 s for the star, and this is shown to be broadly consistent with a MLT/alpha parameter value between 0.8 and 1.2. It is argued that for the DBV pulsators the measured value of tau_0 is a better estimate of the relative stellar surface temperatures than those obtained via spectroscopic techniques.

[24]  arXiv:1412.5688 [pdf, ps, other]
Title: Variable stars in two open clusters within the Kepler 2-Campaign-0 field: M 35 and NGC 2158
Comments: 12 pages, 11 figures (4 at low resolution), 2 tables. Accepted for publication in MNRAS on December 17, 2014. Electronic materials available at the url this http URL , and later on the Journal and at the CDS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We present a multi-year survey aimed at collecting (1) high-precision (~5 milli-mag), (2) fast-cadence (~3 min), and (3) relatively long duration (~10 days) multi-band photometric series. The goal of the survey is to discover and characterize efficiently variable objects and exoplanetary transits in four fields containing five nearby open clusters spanning a broad range of ages. More in detail, our project will (1) constitute a preparatory survey for HARPS-N@TNG, which will be used for spectroscopic follow-up of any target of interest that this survey discovers or characterizes, (2) measure rotational periods and estimate the activity level of targets we are already monitoring with HARPS and HARPS-N for exoplanet transit search, and (3) long term characterization of selected targets of interest in open clusters within the planned K2 fields. In this first paper we give an overview of the project, and report on the variability of objects within the first of our selected fields, which contains two open clusters: M 35 and NGC 2158. We detect 519 variable objects, 273 of which are new discoveries, while the periods of most of the previously known variables are considerably improved.

[25]  arXiv:1412.5692 [pdf, other]
Title: The width of gamma-ray burst spectra
Comments: 5 pages, 3 figures. Accepted for publication in Monthly Notices of the Royal Astronomical Society
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The emission processes active in the highly relativistic jets of gamma-ray bursts (GRBs) remain unknown. In this paper we propose a new measure to describe spectra: the width of the $EF_E$ spectrum, a quantity dependent only on finding a good fit to the data. We apply this to the full sample of GRBs observed by Fermi/GBM and CGRO/BATSE. The results from the two instruments are fully consistent. We find that the median widths of spectra from long and short GRBs are significantly different (chance probability $<10^{-6}$). The width does not correlate with either duration or hardness, and this is thus a new, independent distinction between the two classes. Comparing the measured spectra with widths of spectra from fundamental emission processes -- synchrotron and blackbody radiation -- the results indicate that a large fraction of GRB spectra are too narrow to be explained by synchrotron radiation from a distribution of electron energies: for example, 78% of long GRBs and 85% of short GRBs are incompatible with the minimum width of standard slow cooling synchrotron emission from a Maxwellian distribution of electrons, with fast cooling spectra predicting even wider spectra. Photospheric emission can explain the spectra if mechanisms are invoked to give a spectrum much broader than a blackbody.

[26]  arXiv:1412.5695 [pdf, ps, other]
Title: The Rate of Gas Accretion onto Black Holes Drives Jet Velocity
Comments: Accepted for publication in ApJ letters, 5 pages, 2 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Accreting black holes are observed to launch relativistic, collimated jets of matter and radiation. In some sources, discrete ejections have been detected with highly relativistic velocities. These particular sources typically have very high mass accretion rates, while sources lower knot velocities are predominantly associated with black holes with relatively low mass accretion rates. We quantify this behavior by examining knot velocity with respect to X-ray luminosity, a proxy for mass accretion rate onto the black hole. We find a positive correlation between the mass-scaled X-ray luminosity and jet knot velocity. In addition, we find evidence that the jet velocity is also a function of polar angle, supporting the "spine-sheath" model of jet production. Our results reveal a fundamental aspect of how accretion shapes mechanical feedback from black holes into their host environments.

[27]  arXiv:1412.5696 [pdf, other]
Title: A fussy revisitation of antiprotons as a tool for Dark Matter searches
Comments: 19 pages, 6 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Phenomenology (hep-ph)

Antiprotons are regarded as a powerful probe for Dark Matter (DM) indirect detection and indeed current data from PAMELA have been shown to lead to stringent constraints. However, in order to exploit their constraining/discovery power properly and especially in anticipation of the exquisite accuracy of upcoming data from AMS, great attention must be put into effects (linked to their propagation in the Galaxy) which may be perceived as subleasing but actually prove to be quite relevant. We revisit the computation of the astrophysical background and of the DM antiproton fluxes fully including the effects of: diffusive reacceleration, energy losses including tertiary component and solar modulation (in a force field approximation). We show that their inclusion can somewhat modify the current bounds, even at large DM masses, and that a wrong interpretation of the data may arise if they are not taken into account. The numerical results for the astrophysical background are provided in terms of fit functions; the results for Dark Matter are incorporated in the new release of the PPPC4DMID.

[28]  arXiv:1412.5699 [pdf, ps, other]
Title: Thermal instability and multi-phase interstellar medium in the first galaxies
Comments: 11 pages, 8 figures, submitted to ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We examine the linear stability and nonlinear growth of the thermal instability in isobarically contracting gas with various metallicities and FUV field strengths. When the H2 cooling is suppressed by FUV fields (G_0>10^-3) or the metallicity is high enough (Z/Zs>10^-3), the interstellar medium is thermally unstable in the temperature range 100-7000 K owing to the cooling by CII and OI fine-structure lines. In this case, a bi-phasic medium with a bimodal density probability distribution is formed as a consequence of the thermal instability. The characteristic scales of the thermal instability become smaller with increasing metallicity. Comparisons of the nonlinear simulations with different resolution indicates that the maximum scale of the thermal instability should be resolved with more than 60 cells to follow runaway cooling driven by the thermal instability. Under sufficiently weak FUV fields and with low metallcity, the density range of the thermal instability shrinks owing to dominance of H2 cooling. As the FUV intensity is reduced, bi-phasic structure becomes less remarkable and disappears eventually. Our basic results suggest that, in early galaxies, i) the thermal instability has little effect for the medium with Z/Zs<10^-4, ii) fragmentation by the thermal instability could determine mass spectrum of star clusters for 10^-4<Z/Zs<0.04, and iii) thermally bistable turbulent interstellar medium like our galaxy becomes ubiquitous for Z/Zs>0.04, although the threshold metallicity depends on the conditions such as thermal pressure, FUV strength and redshift.

[29]  arXiv:1412.5715 [pdf, ps, other]
Title: Black hole and nuclear cluster scaling relations: M_bh ~ M_nc^{2.7+/-0.7}
Comments: Invited talk. IAU Symposium 312, "Star Clusters and Black Holes in Galaxies across Cosmic Time", eds. F.Liu and R.Spurzem. 5 conference-sized pages
Subjects: Astrophysics of Galaxies (astro-ph.GA)

There is a growing array of supermassive black hole and nuclear star cluster scaling relations with their host spheroid, including a bent (black hole mass)-(host spheroid mass) M_bh-M_sph relation and different (massive compact object mass)-(host spheroid velocity dispersion) M_mco-sigma relations for black holes and nuclear star clusters. By combining the observed M_bh ~ sigma^(5.5) relation with the observed M_nc ~ sigma^(1.6--2.7) relation, we derive the expression M_bh ~ (M_nc)^(2--3.4), which should hold until the nuclear star clusters are eventually destroyed in the larger core-Sersic spheroids. This new mass scaling relation helps better quantify the rapid evolutionary growth of massive black holes in dense star clusters, and the relation is consistently recovered when coupling the observed M_nc ~ (M_sph)^(0.6--1.0) relation with the recently observed quadratic relation M_bh ~ (M_sph)^2 for Sersic spheroids.

[30]  arXiv:1412.5724 [pdf, ps, other]
Title: Puoko-nui: a flexible high-speed photometric system
Comments: 8 pages, 9 figures, 2 tables
Journal-ref: MNRAS 440 pp1490-1497 (2014)
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

We describe a portable CCD-based instrumentation system designed to efficiently undertake high time precision fast photometry. The key components of the system are (1) an externally triggered commercial frame-transfer CCD, (2) a custom GPS-derived time source, and (3) flexible software for both instrument control and online analysis/display. Two working instruments that implement this design are described. The New Zealand based instrument employs a Princeton Instruments (PI) 1k x 1k CCD and has been used with the 1 m telescope at Mt John University Observatory, while the other uses a newer 1k x 1k electron-multiplying CCD supplied by PI and is based at the University of Texas at Austin. We include some recent observations that illustrate the capabilities of the instruments.

[31]  arXiv:1412.5741 [pdf, ps, other]
Title: Star formation in turbulent molecular clouds with colliding flow
Comments: 22 pages, 18 figures, accepted for publication in ApJ
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

Using self-gravitational hydrodynamical numerical simulations, we investigated the evolution of high-density turbulent molecular clouds swept by a colliding flow. The interaction of shock waves due to turbulence produces networks of thin filamentary clouds with a sub-parsec width. The colliding flow accumulates the filamentary clouds into a sheet cloud and promotes active star formation for initially high-density clouds. Clouds with a colliding flow exhibit a finer filamentary network than clouds without a colliding flow. The probability distribution functions (PDFs) for the density and column density can be fitted by lognormal functions for clouds without colliding flow. When the initial turbulence is weak, the column density PDF has a power-law wing at high column densities. The colliding flow considerably deforms the PDF, such that the PDF exhibits a double peak. The stellar mass distributions reproduced here are consistent with the classical initial mass function with a power-law index of $-1.35$ when the initial clouds have a high density. The distribution of stellar velocities agrees with the gas velocity distribution, which can be fitted by Gaussian functions for clouds without colliding flow. For clouds with colliding flow, the velocity dispersion of gas tends to be larger than the stellar velocity dispersion. The signatures of colliding flows and turbulence appear in channel maps reconstructed from the simulation data. Clouds without colliding flow exhibit a cloud-scale velocity shear due to the turbulence. In contrast, clouds with colliding flow show a prominent anti-correlated distribution of thin filaments between the different velocity channels, suggesting collisions between the filamentary clouds.

[32]  arXiv:1412.5743 [pdf, other]
Title: Astronomy below the Survey Threshold
Comments: 13 pages, 5 figures, to appear as part of 'Continuum Science' in Proceedings 'Advancing Astrophysics with the SKA (AASKA14)' [PoS(AASKA14)172]
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO); Instrumentation and Methods for Astrophysics (astro-ph.IM)

Astronomy at or below the 'survey threshold' has expanded significantly since the publication of the original 'Science with the Square Kilometer Array' in 1999 and its update in 2004. The techniques in this regime may be broadly (but far from exclusively) defined as 'confusion' or 'P(D)' analyses (analyses of one-point statistics), and 'stacking', accounting for the flux-density distribution of noise-limited images co-added at the positions of objects detected/isolated in a different waveband. Here we discuss the relevant issues, present some examples of recent analyses, and consider some of the consequences for the design and use of surveys with the SKA and its pathfinders.

[33]  arXiv:1412.5749 [pdf, ps, other]
Title: Can galactic dark matter substructure contribute to the cosmic gamma-ray anisotropy?
Authors: J.U. Lange, M.-C. Chu
Comments: accepted for publication in MNRAS
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

The annihilation of dark matter (DM) particles in the Milky Way can contribute to the diffuse gamma-ray background (DGRB). Due to the presence of substructures, this emission will appear anisotropic in a predictable way. We generate full-sky maps of the gamma-ray emission in galactic substructures from results of the high-resolution Via Lactea II N-body simulation of the Milky Way DM halo. We calculate the anisotropy pattern, taking into account different radial profiles of the DM distribution in substructures, cosmic variance, and the detection threshold, and compare it to the anisotropy in the DGRB observed by the Fermi Large Area Telescope (LAT). By comparing the upper limits on the DM self-annihilation cross-section, <$\sigma v$>, implied by the anisotropy to the intensity of the DGRB and detected sources in the LAT 2-yr Point Source Catalog, we find that galactic substructure cannot contribute to the anisotropies in the DGRB without strongly violating these observations. Our results challenge the perception that small-scale anisotropies in the DGRB can be used as a probe of DM annihilation in galactic subhaloes.

[34]  arXiv:1412.5753 [pdf, other]
Title: The star-formation history of the Universe with the SKA
Authors: Matt J. Jarvis (1,2), Nick Seymour (3), Jose Afonso (4,5), Philip Best (6), Rob Beswick (7), Ian Heywood (8,9), Minh Huynh (10), Eric Murphy (11), Isabella Prandoni (12), Eva Schinnerer (13), Chris Simpson (14), Mattia Vaccari (2), Sarah White (1) ((1) Oxford, (2) University of the Western Cape, (3) Curtin, (4) OAL, Lisbon, (5) Univ. Lisbon, (6) IfA, Edinburgh, (7) Manchester, (8) CSIRO, (9) Rhodes University, (10) UWA, (11) IPAC, Caltech, (12) INAF Bologna, (13) MPIA, (14) Liverpool John Moores)
Comments: 19 pages, to appear as part of 'Continuum Science' in Proceedings 'Advancing Astrophysics with the SKA (AASKA14)068'
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Radio wavelengths offer the unique possibility of tracing the total star-formation rate in galaxies, both obscured and unobscured. As such, they may provide the most robust measurement of the star-formation history of the Universe. In this chapter we highlight the constraints that the SKA can place on the evolution of the star-formation history of the Universe, the survey area required to overcome sample variance, the spatial resolution requirements, along with the multi-wavelength ancillary data that will play a major role in maximising the scientific promise of the SKA. The required combination of depth and resolution means that a survey to trace the star formation in the Universe should be carried out with a facility that has a resolution of at least ~0.5arcsec, with high sensitivity at < 1 GHz. We also suggest a strategy that will enable new parameter space to be explored as the SKA expands over the coming decade.

[35]  arXiv:1412.5754 [pdf, other]
Title: The first stars: CEMP--no stars and signatures of spinstars
Comments: 17 pages, 9 figures, 2 tables, in press for Astronomy and Astrophysics
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

(Abridged) The CEMP--no stars are "carbon-enhanced-metal-poor" stars that in principle show no evidence of s-- and r--elements from neutron captures. We try to understand the origin and nucleosynthetic site of their peculiar CNO, Ne--Na, and Mg--Al abundances. We compare the observed abundances to the nucleosynthetic predictions of AGB models and of models of rotating massive stars with internal mixing and mass loss. We also analyze the different behaviors of $\alpha$-- and CNO--elements, as well the abundances of elements involved in the Ne--Na and Mg--Al cycles. We show that CEMP-no stars exhibit products of He--burning that have gone through partial mixing and processing by the CNO cycle, producing low $^{12}$C/$^{13}$C and a broad variety of [C/N] and [O/N] ratios. From a $^{12}$C/$^{13}$C vs. [C/N] diagram, we conclude that neither the yields of AGB stars (in binaries or not) nor the yields of classic supernovae can fully account for the observed CNO abundances in CEMP-no stars. Better agreement is obtained once the chemical contribution by stellar winds of fast-rotating massive stars is taken into account, where partial mixing takes place, leading to various amounts of CNO being ejected. CEMP--no stars present a wide variety in the [C/Fe], [N/Fe], [O/Fe], [Na/Fe], [Mg/Fe], [Al/Fe], and [Sr/Fe] ratios. We show that back-and-forth, partial mixing between the He-- and H--regions may account for this variety. Some s--elements, mainly of the first peak, may even be produced by these processes in a small fraction of the CEMP--no stars. We propose a classification scheme for the CEMP--no and low--s stars, based on the changes in composition produced by these successive back-and-forth mixing motions.

[36]  arXiv:1412.5759 [pdf, ps, other]
Title: Eclipse Timing Variation Analyses of Eccentric Binaries with Close Tertiaries in the Kepler field
Comments: 83 pages, including 32 pages (26 tables) of tabulated Times of Minima data for the analysed 26 systems; submitted to MNRAS (revised version)
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)

We report eclipse timing variation analyses of 26 compact hierarchical triple stars comprised of an eccentric eclipsing ('inner') binary and a relatively close tertiary component found in the {\em Kepler} field. We simultaneously fit the primary and secondary $O-C$ curves of each system for the light-travel time effect (LTTE), as well as dynamical perturbations caused by the tertiary on different timescales. For the first time, we include those contributions of three-body interactions which originate from the eccentric nature of the inner binary. These effects manifest themselves both on the period of the triple system, $P_2$, and on the longer "apse-node" timescale. We demonstrate that consideration of the dynamically forced rapid apsidal motion yields an efficient and independent tool for the determination of the binary orbit's eccentricity and orientation, as well as the 3D configuration of the triple. Modeling the forced apsidal motion also helps to resolve the degeneracy between the shapes of the LTTE and the dynamical delay terms on the $P_2$ timescale, due to the strong dependence of the apsidal motion period on the triple's mass ratio. This can lead to the independent determination of the binary and tertiary masses without the need for independent radial velocity measurements. Through the use of our analytic method for fitting $O-C$ curves we have obtained robust solutions for system parameters for the ten most ideal triples of our sample, and only somewhat less robust, but yet acceptable, fits for the remaining systems. Finally we study the results of our 26 system parameter fits via a set of distributions of various physically important parameters, including mutual inclination angle, and mass and period ratios.

[37]  arXiv:1412.5760 [pdf, ps, other]
Title: New Halpha flux measurements in nearby dwarf galaxies
Comments: 22 pages, 1 table, 1 appendix
Journal-ref: Astrophysical Bulletin, (2014), Volume 69, pp 390-408
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present the emission Halpha line images for 40 galaxies of the Local Volume based on the observations at the 6-meter BTA telescope. Among them there are eight satellites of the Milky Way and Andromeda M31 as well as two companions to M51. The measured Halpha fluxes of the galaxies are used to determine their integral (SFR) and specific (sSFR) star formation rates. The values of Log(sSFR) for the observed galaxies lie in the range of (-9, -14)/yr.
A comparison of SFR estimates derived from the Halpha flux and from the ultraviolet FUV flux yields evidence that two blue compact galaxies MRK 475 and LV J1213+2957 turn out to be at a sharp peak of their star-burst activity.

[38]  arXiv:1412.5763 [pdf, ps, other]
Title: The HIFI spectral survey of AFGL 2591 (CHESS). III. Chemical structure of the protostellar envelope
Authors: Maja Kazmierczak-Barthel (SRON), Dimitri Semenov (MPIA), Floris van der Tak (SRON & U Groningen), Luis Chavarría (U Chile), Matthijs van der Wiel (ISIS)
Comments: Accepted for publication in A&A; 15 pages, 6 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We aim to understand the rich chemical composition of AFGL 2591, a prototypical isolated high-mass star-forming region.
Based on HIFI and JCMT data, the molecular abundances of species found in the protostellar envelope of AFGL 2591 were derived with the Monte Carlo radiative transfer code RATRAN, assuming either constant values or 1D stepwise radial profiles as abundance distributions. The reconstructed 1D abundances were compared with the results of time-dependent gas-grain chemical modeling, considering ages of 10,000 to 50,000 years, cosmic-ray ionization rates of 0.5 to 50 times 10^-16 s^-1, uniformly-sized 0.1-1 micron dust grains, a dust/gas ratio of 1%, and several sets of initial molecular abundances with C/O <1 and >1.
Constant abundance models give good fits to the data for CO, CN, CS, HCO+, H2CO, N2H+, C2H, NO, OCS, OH, H2CS, O, C, C+, and CH. Models with an abundance jump at 100 K give good fits to the data for NH3, SO, SO2, H2S, H2O, HCl, and CH3OH. For HCN and HNC, the best models have an abundance jump at 230 K. The time-dependent chemical model can accurately explain abundance profiles of 15 out of these 24 species. The jump-like radial profiles for key species like HCO+, NH3, and H2O are consistent with the outcome of the time-dependent chemical modeling. The best-fit model has a chemical age of 10-50 kyr, a solar C/O ratio of 0.44, and a cosmic-ray ionization rate of 5 x 10^-17 s^-1; grain properties and external UV intensity do not affect the calculated chemical structure much.
We thus demonstrate that simple constant or jump-like abundance profiles agree with time-dependent chemical modeling for most key C-, O-, N-, and S-bearing molecules. The main exceptions are species with very few observed transitions (C, O, C+, and CH), with a poorly established chemical network (HCl, H2S) or whose chemistry is strongly affected by surface processes (CH3OH).

[39]  arXiv:1412.5771 [pdf, ps, other]
Title: The Interplay between SF and AGN Activity, and its role in Galaxy Evolution
Comments: 16 pages, 3 figures to appear as part of "Continuum Science" in proceedings of "Advancing Astrophysics with the Square Kilometre Array" PoS(AASKA14)083
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

It has become apparent that active galactic nuclei (AGN) may have a significant impact on the growth and evolution of their host galaxies and vice versa but a detailed understanding of the interplay between these processes remains elusive. Deep radio surveys provide a powerful, obscuration-independent tool for measuring both star formation and AGN activity in high-redshift galaxies. Multiwavelength studies of deep radio fields show a composite population of star-forming galaxies and AGN, with the former dominating at the lowest flux densities (S$_{1.4\mathrm{GHz}}<$100~$\mu$Jy). The sensitivity and resolution of the SKA will allow us to identify, and separately trace, the total star formation in the bulges of individual high-redshift galaxies, the related nuclear activity and any star formation occurring on larger scales within a disc. We will therefore gain a detailed picture of the apparently simultaneous development of stellar populations and black holes in the redshift range where both star-formation and AGN activity peak (1$\leq$z$\leq$4). In this chapter we discuss the role of the SKA in studying the connection between AGN activity and galaxy evolution, and the most critical technical requirements for such of studies

[40]  arXiv:1412.5784 [pdf, ps, other]
Title: Gas composition of major volatile elements in protoplanetary discs and its implication for planet formation
Comments: 12 pages, 15 figures. Accepted for publication in A&A
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Direct observations of gaseous exoplanets reveals that their gas envelope is commonly enriched in C/O ratio compared to that of the host star. This has been explained by considering that the gas phase of the disc could be inhomogeneous, exceeding the stellar C/O ratio in regions where these planets formed; but few studies have considered the drift of the gas and the migration of planets. We aim to derive the gas composition in planets to evaluate if the formation of giant planets with an enriched C/O ratio is possible. The study focusses on the effects of different processes on the C/O ratio like the disc evolution, the drift of gas, and the migration of the planet. We used our previous models for computation of the chemical composition together with the planet formation model of Alibert et al. (2013), to which we added the composition and drift of the gas phase of the disc composed of major volatile species, H2 and He. The study focusses on the region where ice lines are present and influence the C/O ratio of the planets. Modelling shows that the condensation of volatile species allows for C/O enrichment in specific parts of the protoplanetary disc, of up to 4 times the solar value. This leads to the formation of planets that can be enriched in C/O in their envelope up to 3 times the solar value. The migration of planets, the evolution of the gas phase, and the irradiation of the disc enables the evolution of the initial C/O ratio with a decrease in the outer part of the disc and an increase in the inner part. The total C/O ratio of the planets is governed by the contribution of ices accreted, suggesting that high C/O ratios measured in planetary atmospheres are indicative of a lack of exchange of material between the core of a planet and its envelope or an observational bias, and suggesting that the observed C/O ratio is not representative of the total C/O ratio of the planet.

[41]  arXiv:1412.5785 [pdf, other]
Title: Constraints on the gas content of the Fomalhaut debris belt; Can gas-dust interactions explain the belt's morphology?
Comments: 5 pages, 3 figures, accepted for publication in A&A
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)

Context: The 440 Myr old main-sequence A-star Fomalhaut is surrounded by an eccentric debris belt with sharp edges. Such a morphology is usually attributed to planetary perturbations, but the orbit of the only planetary candidate detected so far, Fomalhaut b, is too eccentric to efficiently shape the belt. Alternative models that could account for the morphology without invoking a planet are stellar encounters and gas-dust interactions.
Aims: We aim to test the possibility of gas-dust interactions as the origin of the observed morphology by putting upper limits on the total gas content of the Fomalhaut belt.
Methods: We derive upper limits on the CII 158 $\mu$m and OI 63 $\mu$m emission by using non-detections from the PACS instrument onboard the Herschel Space Observatory. Line fluxes are converted into total gas mass using the non-LTE code RADEX. We consider two different cases for the elemental abundances of the gas: solar abundances and abundances similar to those observed for the gas in the $\beta$ Pictoris debris disk.
Results: The gas mass is shown to be below the millimetre dust mass by a factor of at least $\sim$3 (for solar abundances) respectively $\sim$300 (for $\beta$ Pic-like abundances).
Conclusions: The lack of gas co-spatial with the dust implies that gas-dust interactions cannot efficiently shape the Fomalhaut debris belt. The morphology is therefore more likely due to a yet unseen planet (Fomalhaut c) or stellar encounters.

[42]  arXiv:1412.5793 [pdf, ps, other]
Title: Enabling the next generation of cm-wavelength studies of high-redshift molecular gas with the SKA
Authors: J. Wagg (1), E. Da Cunha (2), C. L. Carilli (3 and 4), F. Walter (2), M. Aravena (5), I. Heywood (6 and 7), J. Hodge (8), E. Murphy (9), D. Riechers (10), M. Sargent (11), R. Wang (12) ((1) SKAO, (2) MPIA, (3) NRAO, (4) Cavendish Laboratory, (5) Universidad Diego Portales, (6) CASS, (7) RATT, (8) NRAO, (9) Caltech, (10) Cornell University, (11) University of Sussex, (12) KIAA, Peking)
Comments: 10 pages, to be published in Proceedings of Science: "Advancing Astrophysics with the Square Kilometre Array", PoS(AASKA14)161
Subjects: Astrophysics of Galaxies (astro-ph.GA)

The Square Kilometre Array will be a revolutionary instrument for the study of gas in the distant Universe. SKA1 will have sufficient sensitivity to detect and image atomic 21 cm HI in individual galaxies at significant cosmological distances, complementing ongoing ALMA imaging of redshifted high-J CO line emission and far-infrared interstellar medium lines such as [CII] 157.7 um. At frequencies below ~50 GHz, observations of redshifted emission from low-J transitions of CO, HCN, HCO+, HNC, H2O and CS provide insight into the kinematics and mass budget of the cold, dense star-forming gas in galaxies. In advance of ALMA band 1 deployment (35 to 52 GHz), the most sensitive facility for high-redshift studies of molecular gas operating below 50~GHz is the Karl G. Jansky Very Large Array (VLA). Here, we present an overview of the role that the SKA could play in molecular emission line studies during SKA1 and SKA2, with an emphasis on studies of the dense gas tracers directly probing regions of active star-formation.

[43]  arXiv:1412.5800 [pdf, other]
Title: COSMIC-LAB: Terzan 5 as a fossil remnant of the Galactic bulge formation epoch
Authors: Davide Massari
Comments: Ph.D. Thesis. Alma Mater Studiorum-University of Bologna, Ph.D. in Astronomy, Cycle XXVII. Thesis defense in December 2014
Subjects: Astrophysics of Galaxies (astro-ph.GA)

The formation and evolution of galaxy bulges is one of the most debated topics in the modern astrophysics. One approach to address this issue is to look at the Galactic bulge since it is the closest. According to some theoretical models, our bulge may have built up from the merger of substructures formed from the fragmentation of a gaseous disk in the early phases of Galactic evolution. We may have discovered the remnant of one of these substructures in the stellar system Terzan 5. In fact, Terzan 5 hosts two stellar populations with quite different iron abundances, thus suggesting it once was far more massive than today. Moreover, its peculiar chemistry strikingly resembles that observed in the Galactic bulge. In this Thesis we performed a detailed photometric and spectroscopic analysis of this cluster to determine its formation and evolution. Form the photometric point of view we built a high-resolution differential reddening map in the direction of the system and we measured relative proper motions to separate its member population from the contaminating bulge and disk stars. From the spectroscopic point of view we measured abundances for more than 600 stars belonging to Terzan 5 and its surroundings in order to build the largest field-decontaminated metallicity distribution for this system. We find that the metallicity distribution is extremely broad (>1 dex) and we discovered a third, metal-poor and alpha-enhanced population with average [Fe/H]=-0.8 dex. The striking similarity between Terzan 5 and the bulge in terms of their chemical formation and evolution that is clearly revealed by this Thesis suggests that Terzan 5 formed in situ with the Galactic bulge. In particular its metal-poor populations trace the early stages of the bulge formation, while its most metal-rich component may contain crucial information on the bulge more recent evolution.

[44]  arXiv:1412.5801 [pdf, other]
Title: Non-thermal emission from galaxy clusters: feasibility study with SKA1
Comments: 12 pages, 5 figures, to appear as part of 'Continuum Science' in Proceedings 'Advancing Astrophysics with the SKA (AASKA14)'
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Galaxy clusters are known to host a variety of extended radio sources: tailed radio galaxies whose shape is modelled by the interaction with the intra-cluster medium (ICM); radio bubbles filling cavities in the ICM distribution and rising buoyantly through the thermal gas; diffuse giant radio sources ("halos" and "relics") revealing the presence of relativistic electrons and magnetic fields in the intra-cluster volume. It is currently the subject of an active debate how the non-thermal components that we observe at radio wavelengths affect the physical properties of the ICM and depend on the dynamical state of galaxy clusters. In this work we start our SKA1 feasibility study of the "radio cluster zoo" through simulations of a typical radio-loud cluster, hosting several bright tailed radio galaxies and a diffuse radio halo. Realistic simulations of SKA1 observations are obtained through the MeqTrees software. A new deconvolution algorithm, based on sparse representations and optimised for the detection of faint diffuse astronomical sources, is tested and compared to the classical CLEAN method.

[45]  arXiv:1412.5807 [pdf, ps, other]
Title: The $E_{\rm p}$ - $E_{\rm iso}$ relation and the internal shock model
Comments: 7 pages, 4 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The validity of the $E_{\rm p}$ - $E_{\rm iso}$ correlation in gamma-ray bursts and the possibility of explaining the prompt emission with internal shocks are highly debated questions. We study whether the $E_{\rm p}$ - $E_{\rm iso}$ correlation can be reproduced if internal shocks are indeed responsible for the prompt emission, or conversely, if the correlation can be used to constrain the internal shock scenario. We developed a toy model where internal shocks are limited to the collision of only two shells. Synthetic burst populations were constructed for various distributions of the model parameters, such as the injected power in the relativistic outflow, the average Lorentz factor, and its typical contrast between the shells. These parameters can be independent or linked by various relations. Synthetic $E_{\rm p}$ - $E_{\rm iso}$ diagrams are obtained in the different cases and compared with the observed correlation. The reference observed correlation is the one defined by the BAT6 sample, a sample of Swift bursts almost complete in redshift and affected by well-known and reproducible instrumental selection effects. The comparison is then performed with a subsample of synthetic bursts that satisfy the same selection criteria as were imposed on the BAT6 sample. A satisfactory agreement between model and data can often be achieved, but only if several strong constraints are satisfied on both the dynamics of the flow and the microphysics that governs the redistribution of the shock-dissipated energy.

[46]  arXiv:1412.5810 [pdf, other]
Title: SKA studies of nearby galaxies: star-formation, accretion processes and molecular gas across all environments
Authors: R. J. Beswick (JBCA, Manchester), E. Brinks (Hertfordshire), M. A. Perez-Torres (IAA-CSIC), A. M. S. Richards (JBCA, Manchester), S. Aalto (Chalmers), A. Alberdi (IAA-CSIC), M. K. Argo (JBCA, Manchester), I. van Bemmel (JIVE/ASTRON), J. E. Conway (Onsala/Chalmers), C. Dickinson (JBCA, Manchester), D. M. Fenech (UCL), M. D. Gray (JBCA, Manchester), H-R. Klockner (MPIfR-Bonn), E. J. Murphy (IPAC, Caltech), T. W. B. Muxlow (JBCA, Manchester), M. Peel (JBCA, Manchester), A. P. Rushton (Oxford and Southampton), E. Schinnerer (MPIA-Heidelberg)
Comments: 23 pages, 4 figures, to appear as part of 'Continuum Science' in Proceedings 'Advancing Astrophysics with the Square Kilometre Array' PoS(AASKA14)070
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

The SKA will be a transformational instrument in the study of our local Universe. In particular, by virtue of its high sensitivity (both to point sources and diffuse low surface brightness emission), angular resolution and the frequency ranges covered, the SKA will undertake a very wide range of astrophysical research in the field of nearby galaxies. By surveying vast numbers of nearby galaxies of all types with $\mu$Jy sensitivity and sub-arcsecond angular resolutions at radio wavelengths, the SKA will provide the cornerstone of our understanding of star-formation and accretion activity in the local Universe. In this chapter we outline the key continuum and molecular line science areas where the SKA, both during phase-1 and when it becomes the full SKA, will have a significant scientific impact.

[47]  arXiv:1412.5819 [pdf, other]
Title: Internal shocks driven by accretion flow variability in the compact jet of the black hole binary GX 339-4
Comments: 9 pages, 8 figures, 3 tables, accepted for publication in MNRAS
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

In recent years, compact jets have been playing a growing role in the understanding of accreting black hole engines. In the case of X-ray binary systems, compact jets are usually associated with the hard state phase of a source outburst. Recent observations of GX 339-4 have demonstrated the presence of a variable synchrotron spectral break in the mid-infrared band that was associated with its compact jet. In the model used in this study, we assume that the jet emission is produced by electrons accelerated in internal shocks driven by rapid fluctuations of the jet velocity. The resulting spectral energy distribution (SED) and variability properties are very sensitive to the Fourier power spectrum density (PSD) of the assumed fluctuations of the jet Lorentz factor. These fluctuations are likely to be triggered by the variability of the accretion flow which is best traced by the X-ray emission. Taking the PSD of the jet Lorentz factor fluctuations to be identical to the observed X-ray PSD, our study finds that the internal shock model successfully reproduces the radio to infrared SED of the source at the time of the observations as well as the reported strong mid-infrared spectral variability.

[48]  arXiv:1412.5821 [pdf, ps, other]
Title: The evolution of the cluster optical galaxy luminosity function between z=0.4 and 0.9 in the DAFT/FADA survey
Comments: accepted for publication in A&A
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We compute optical galaxy luminosity functions (GLFs) in the B, V, R, and I rest-frame bands for one of the largest medium-to-high-redshift (0.4 < z < 0.9) cluster samples to date in order to probe the abundance of faint galaxies in clusters. We also study how the GLFs depend on cluster redshift, mass, and substructure, and compare the GLFs of clusters with those of the field. We separately investigate the GLFs of blue and red-sequence (RS) galaxies to understand the evolution of different cluster populations. We find that the shapes of our GLFs are similar for the B, V, R, and I bands with a drop at the red GLF faint end that is more pronounced at high-redshift: alpha(red) ~ -0.5 at 0.40 < z < 0.65 and alpha(red) > 0.1 at 0.65 < z < 0.90. The blue GLFs have a steeper faint end (alpha(blue) ~ -1.6) than the red GLFs, that appears to be independent of redshift. For the full cluster sample, blue and red GLFs intersect at M(V) = -20, M(R) = -20.5, and M(I) = -20.3. A study of how galaxy types evolve with redshift shows that late type galaxies appear to become early types between z ~ 0.9 and today. Finally, the faint ends of the red GLFs of more massive clusters appear to be richer than less massive clusters, which is more typical of the lower redshift behaviour. Our results indicate that our clusters form at redshifts higher than z = 0.9 from galaxy structures that already have an established red sequence. Late type galaxies then appear to evolve into early types, enriching the red-sequence between this redshift and today. This effect is consistent with the evolution of the faint end slope of the red-sequence and the galaxy type evolution that we find. Finally, faint galaxies accreted from the field environment at all redshifts might have replaced the blue late type galaxies that converted into early types, explaining the lack of evolution in the faint end slopes of the blue GLFs.

[49]  arXiv:1412.5823 [pdf, ps, other]
Title: The SiO outflow from IRAS 17233-3603 at high resolution
Authors: P.D. Klaassen (1,2), K. G. Johnston (3,4), S. Leurini (5), L.A. Zapata (6) ((1) Leiden Observatory, (2) UK Astronomy Technology Centre, (3) Max Planck Institute for Astronomy, (4) University of Leeds, (5) Max Planck Institut fur Radioastronomie, (6) Centro de Radioastronomia y Astrofisica, UNAM)
Comments: 10 pages, 14 figures, Accepted for publication in A&A
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Context: Jets and outflows are key ingredients in the formation of stars across the mass spectrum. In clustered regions, understanding powering sources and outflow components poses a significant problem. Aims: To understand the dynamics in the outflow(s) from a cluster in the process of forming massive stars. Methods: We use new VLA observations of the molecular gas (SiO, CS, OCS and \molec) in the massive star forming region IRAS 17233-3606 which contains a number of HII regions. We compare these observations to previously published molecular data for this source in order to get a holistic view of the outflow dynamics. Results:We find that the dynamics of the various species can be explained by a single large scale ($\sim 0.15$ pc) outflow when compared to the sizes of the HII regions, with the different morphologies of the blue and red outflow components explained with respect to the morphology of the surrounding envelope. We further find that the direction of the velocity gradients seen in OCS and \molec are suggestive of a combination of rotation and outflow motions in the warm gas surrounding the HII regions near the base of the large scale outflow. Conclusions: Our results show that the massive protostars forming within this region appear to be contributing to a single outflow on large scales. This single large scale outflow is traced by a number of different species as the outflow interacts with its surroundings. On the small scales, there appear to be multiple mechanisms contributing to the dynamics which could be a combination of either a small scale outflow or rotation with the dynamics of the large scale outflow.

[50]  arXiv:1412.5827 [pdf, ps, other]
Title: Radio Observations of Star Forming Galaxies in the SKA era
Comments: 11 pages, 4 figures, to appear in proceedings of "Advancing Astrophysics with the Square Kilometre Array" PoS(AASKA14)082
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We have combined determinations of the epoch-dependent star formation rate (SFR) function with relationships between SFR and radio (synchrotron and free-free) emission to work out detailed predictions for the counts and the redshift distributions of star-forming galaxies detected by planned Square Kilometer Array (SKA) surveys. The evolving SFR function comes from recent models fitting the far-infrared (FIR) to millimeter-wave luminosity functions and the ultraviolet (UV) luminosity functions up to z=10, extended to take into account additional UV survey data. We used very deep 1.4 GHz number counts from the literature to check the relationship between SFR and synchrotron emission, and the 95 GHz South Pole Telescope (SPT) counts of dusty galaxies to test the relationship between SFR and free-free emission. We show that the SKA will allow us to investigate the SFRs of galaxies down to few Msun/yr up to z=10, thus extending by more than two orders of magnitude the high-z SFR functions derived from Herschel surveys. SKA1-MID surveys, down to microJy levels, will detect hundreds of strongly lensed galaxies per square degree; a substantial fraction of them will show at least two images above the detection limits.

[51]  arXiv:1412.5833 [pdf, ps, other]
Title: The impact of the SKA on Galactic Radioastronomy: continuum observations
Comments: 17 pages, 5 figures. To appear in proceedings of "Advancing Astrophysics with the Square Kilometre Array", 2015, PoS(AASKA14)
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

The SKA will be a state of the art radiotelescope optimized for both large area surveys as well as for deep pointed observations. In this paper we analyze the impact that the SKA will have on Galactic studies, starting from the immense legacy value of the all-sky survey proposed by the continuum SWG but also presenting some areas of Galactic Science that particularly benefit from SKA observations both surveys and pointed. The planned all-sky survey will be characterized by unique spatial resolution, sensitivity and survey speed, providing us with a wide-field atlas of the Galactic continuum emission. Synergies with existing, current and planned radio Galactic Plane surveys will be discussed. SKA will give the opportunity to create a sensitive catalog of discrete Galactic radio sources, most of them representing the interaction of stars at various stages of their evolution with the environment: complete census of all stage of HII regions evolution; complete census of late stages of stellar evolution such as PNe and SNRs; detection of stellar winds, thermal jets, Symbiotic systems, Chemically Peculiar and dMe stars, active binary systems in both flaring and quiescent states. Coherent emission events like Cyclotron Maser in the magnetospheres of different classes of stars can be detected. Pointed, deep observations will allow new insights into the physics of the coronae and plasma processes in active stellar systems and single stars, enabling the detection of flaring activity in larger stellar population for a better comprehension of the mechanism of energy release in the atmospheres of stars with different masses and age.

[52]  arXiv:1412.5846 [pdf, ps, other]
Title: The physics of the radio emission in the quiet side of the AGN population with the SKA
Authors: M. Orienti (1), F. D'Ammando (1,2), M. Giroletti (1), G. Giovannini (1,2), F. Panessa (3), ((1) INAF-IRA Bologna, (2) DIFA, University of Bologna, (3) INAF-IAPS Roma)
Comments: 7 pages, to appear as part of 'Continuum Science' in Proceedings of 'Advancing Astrophysics with the SKA (AASKA14)'
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Despite targets of many multiwavelength campaigns, the main physical processes at work in AGN are still under debate. In particular the origin of the radio emission and the mechanisms involved are among the open questions in astrophysics. In the radio-loud AGN population the radio emission is linked to the presence of bipolar outflows of relativistic jets. However, the large majority of the AGN population do not form powerful highly-relativistic jets on kpc scales and are characterized by radio luminosity up to 10^23 W/Hz at 1.4 GHz, challenging our knowledge on the physical processes at the basis of the radio emission in radio-quiet objects. The main mechanisms proposed so far are synchrotron radiation from mildly relativistic mini-jets, thermal cyclo-synchrotron emission by low-efficiency accretion flow (like ADAF or ADIOS), or thermal free-free emission from the X-ray heated corona or wind. The difficulty in understanding the main mechanism involved is related to the weakness of these objects, which precludes the study of non-local radio-quiet AGN. Multifrequency, high-sensitivity radio observations are crucial to constrain the nature of the power engine, and they may help in distinguishing between the contribution from star formation and AGN activity. The advent of the SKA, with its sub-arcsecond resolution and unprecedented sensitivity will allow us to investigate these processes in radio-quiet AGN, even at high redshift for the first time. Both the broad-band radio spectrum and the polarization information will help us in disentangling between non-thermal and thermal origin of the radio emission. The jump in sensitivity of a few order of magnitudes at the (sub-)uJy level will enable us to detect radio emission from a large number of radio-quiet AGN at high redshift, providing a fundamental step in our understanding of their cosmological evolution. (Abridged)

[53]  arXiv:1412.5852 [pdf, ps, other]
Title: Magnetically-driven crustquakes in neutron stars
Comments: 12 pages, 8 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR)

Crustquake events may be connected with both rapid spin-up `glitches' within the regular slowdown of neutron stars, and high-energy magnetar flares. We argue that magnetic field decay builds up stresses in a neutron star's crust, as the elastic shear force resists the Lorentz force's desire to rearrange the global magnetic-field equilibrium. We derive a criterion for crust-breaking induced by a changing magnetic-field configuration, and use this to investigate strain patterns in a neutron star's crust for a variety of different magnetic-field models. Universally, we find that the crust is most liable to break if the magnetic field has a strong toroidal component, in which case the epicentre of the crustquake is around the equator. We calculate the energy released in a crustquake as a function of the fracture depth, finding that it is independent of field strength. Crust-breaking is, however, associated with a characteristic local field strength of $2.4\times 10^{14}$ G for a breaking strain of $0.001$, or $2.4\times 10^{15}$ G at a breaking strain of $0.1$. We find that even the most luminous magnetar giant flare could have been powered by crustal energy release alone.

[54]  arXiv:1412.5853 [pdf, ps, other]
Title: The unusual glitch recoveries of the high magnetic field pulsar J1119$-$6127
Comments: 14 pages, 4 figures; Accepted for publication in MNRAS
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR)

Providing a link between magnetars and radio pulsars, high magnetic field neutron stars are ideal targets to investigate how bursting/magnetospheric activity and braking torque variations are connected to rotational glitches. The last spin-up glitch of the highly magnetised pulsar J1119$-$6127 back in 2007 was the first glitch in a rotationally powered radio pulsar to be accompanied by radiative changes. Moreover, it was followed by an uncommon glitch relaxation that resulted in a smaller spin-down rate relative to the prediction of the pre-glitch timing model. Here, we present 4 years of new radio timing observations and analyse the total of 16 years of timing data for this source. The new data uncover an ongoing evolution of the spin-down rate, thereby allowing us to exclude permanent changes in the external or internal torque as a stand-alone cause of the peculiar features of the glitch recovery. Furthermore, no additional variations of the radio pulse profile are detected, strengthening the association of the previously observed transient emission features with the glitching activity. A self-consistent measurement of the braking index yields a value $n\simeq2.7$, indicating a trajectory in the $P-\dot{P}$ plane inclined towards the magnetars. Such a potential evolutionary link might be strengthened by a, possibly permanent, reduction of $\sim15\%$ in $n$ at the epoch of the 2007 glitch.

[55]  arXiv:1412.5857 [pdf, other]
Title: The StEllar Counterparts of COmpact high velocity clouds (SECCO) survey. I. Photos of ghosts
Authors: M. Bellazzini (1), G. Beccari (2), G. Battaglia (3,1), N. Martin (4,5), V. Testa (6), R. Ibata (4), M. Correnti (7), F. Cusano (1), E. Sani (8) ((1) INAF - OA Bologna, (2) ESO Chile, (3) IAC La Laguna, (4) Obs. de Strasbourg - CNRS, (5) MPIA Heidelberg, (6) INAF - OA Roma, (7) STScI Baltimore, (8) INAF OA Arcetri)
Comments: Accepted for publication by A&A. PdfLaTex. 24 pages, 27 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present an imaging survey aimed at searching for the stellar counterparts of recently discovered ultra-compact high-velocity HI clouds (UCHVC). Adams et al. (2013) proposed these clouds to be candidate mini-haloes in the Local Group and/or its surroundings, within a distance range of 0.25-2.0 Mpc. Using the Large Binocular Telescope we obtain wide-field (~ 23' X 23') g- and r-band images of the twenty-five most promising and most compact clouds among the fifty-nine identified by Adams et al. Careful visual inspection of all the images does not reveal any stellar counterpart even slightly resembling LeoP, the only local dwarf galaxy that was found as a counterpart to a previously detected high velocity cloud. Only a possible distant (D>3.0 Mpc) counterpart to HVC274.68+74.70-123 has been identified on our images. The point source photometry in the central 17.3' X 7.7' chips reaches r<= 26.5, and is expected to contain most of the stellar counterparts to the UCHVCs. However, no obvious stellar over-density is detected in any of our fields, in marked contrast to our comparison LeoP field in which the dwarf galaxy is detected at a >30 sigma significance level. Only HVC352.45+59.06+263 may be associated with a weak over-density, whose nature cannot be ascertained with our data. Sensitivity tests shows that our survey would have detected any dwarf galaxy dominated by an old stellar population, with an integrated absolute magnitude M_V<= -8.0, a half-light radius r_h<= 300 pc, and lying within 1.5 Mpc from us, thereby confirming that it is unlikely that the observed UCHVCs are associated with stellar counterparts typical of known Local Group dwarf galaxies.

[56]  arXiv:1412.5868 [pdf, other]
Title: Galaxy Cluster Science with the Sunyaev-Zel'dovich Effect
Comments: To appear as part of 'Continuum Science' in Proceedings 'Advancing Astrophysics with the Square Kilometre Array' PoS(AASKA14)170
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Studying galaxy clusters through their Sunyaev-Zel'dovich (SZ) imprint on the Cosmic Microwave Background has many important advantages. The total SZ signal is an accurate and precise tracer of the total pressure in the intra-cluster medium and of cluster mass, the key observable for using clusters as cosmological probes. Band 5 observations with SKA-MID towards cluster surveys from the next generation of X-ray telescopes such as e-ROSITA and from Euclid will provide the robust mass estimates required to exploit these samples. This will be especially important for high redshift systems, arising from the SZ's unique independence to redshift. In addition, galaxy clusters are very interesting astrophysical systems in their own right, and the SKA's excellent surface brightness sensitivity down to small angular scales will allow us to explore the detailed gas physics of the intra-cluster medium.

[57]  arXiv:1412.5884 [pdf, ps, other]
Title: Unravelling lifecycles & physics of radio-loud AGN in the SKA era
Comments: to appear as part of 'Continuum Science' in Proceedings 'Advancing Astrophysics with the SKA (AASKA14), PoS(AASKA14)173
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Radio-loud AGN (>10^{22} W/Hz at 1.4 GHz) will be the dominant bright source population detected with the SKA. The high resolution that the SKA will provide even in wide-area surveys will mean that, for the first time sensitive, multi-frequency total intensity and polarisation imaging of large samples of radio-loud active galactic nuclei (AGN) will become available. The unprecedented sensitivity of the SKA coupled with its wide field of view capabilities will allow identification of objects of the same morphological type (i.e. the entire FR I, low- and high-luminosity FR II, disturbed morphology as well as weak radio-emitting AGN populations) up to high redshifts (z~4 and beyond), and at the same stage of their lives, from the youngest CSS/GPS sources to giant and fading (dying) sources, through to those with restarted activity radio galaxies and quasars. Critically, the wide frequency coverage of the SKA will permit analysis of same-epoch rest-frame radio properties, and the sensitivity and resolution will allow full cross-identification with multi-waveband data, further revealing insights into the physical processes driving the evolution of these radio sources. In this chapter of the SKA Science Book we give a summary of the main science drivers in the studies of lifecycles and detailed physics of radio-loud AGN, which include radio and kinetic luminosity functions, AGN feedback, radio-AGN triggering, radio-loud AGN unification and cosmological studies. We discuss the best parameters for the proposed SKA continuum surveys, both all-sky and deep field, in the light of these studies.

[58]  arXiv:1412.5895 [pdf, other]
Title: Uncertainties in asteroseismic grid-based estimates of stellar ages. SCEPtER: Stellar CharactEristics Pisa Estimation gRid
Comments: A&A accepted. Abstract shortened
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We study the impact on stellar age determination by means of grid-based techniques adopting asteroseismic constraints of the uncertainty in the radiative opacity, in the initial helium abundance, in the mixing-length value, in the convective core overshooting, and in the microscopic diffusion efficiency adopted in stellar model computations. We extended our SCEPtER grid (Valle et al. 2014) to include stars with mass in the range [0.8; 1.6] Msun and evolutionary stages from the ZAMS to the central hydrogen depletion. The current typical uncertainty in the observations accounts for 1 sigma statistical relative error in age determination which in mean ranges from about -35% to +42%, depending on the mass. However, due to the strong dependence on the evolutionary phase, the age relative error can be higher than 120% for stars near the ZAMS, while it is typically of the order of 20% or lower in the advanced main-sequence phase. The systematic bias on age determination due to a variation of $\pm$ 1 in the helium-to-metal enrichment ratio Delta Y/Delta Z is about one-forth of the statistical error in the first 30% of the evolution while it is negligible for more evolved stages. The maximum bias due to the presence of the convective core overshooting is of -7% and -13% for mild and strong overshooting scenarios. For all the examined models the impact of a variation of $\pm$ 5 in the radiative opacity was found to be negligible. The most important source of bias are the uncertainty in the mixing-length value alpha_ml and the neglect of microscopic diffusion. Each of these effects accounts for a bias which is nearly equal to the random error uncertainty. Comparison of the results of our technique with other grid techniques on a set of common stars showed a general agreement. However, the adoption of a different grid can account for a variation in the mean estimated age up to 1 Gyr.

[59]  arXiv:1412.5899 [pdf, other]
Title: The HU Aqr planetary system hypothesis revisited
Comments: 18 pages, 16 figures, 4 tables, accepted to Monthly Notices of the Royal Astronomical Society (MNRAS)
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

We study the mid-egress eclipse timing data gathered for the cataclysmic binary HU Aquarii during the years 1993-2014. The (O-C) residuals were previously attributed to a single ~7 Jupiter mass companion in ~5 au orbit or to a stable 2-planet system with an unconstrained outermost orbit. We present 22 new observations gathered between June, 2011 and July, 2014 with four instruments around the world. They reveal a systematic deviation of ~60 - 120 seconds from the older ephemeris. We re-analyse the whole set of the timing data available. Our results provide an erratum to the previous HU Aqr planetary models, indicating that the hypothesis for a third and fourth body in this system is uncertain. The dynamical stability criterion and a particular geometry of orbits rule out coplanar 2-planet configurations. A putative HU Aqr planetary system may be more complex, e.g., highly non-coplanar. Indeed, we found examples of 3-planet configurations with the middle planet in a retrograde orbit, which are stable for at least 1Gyr, and consistent with the observations. The (O-C) may be also driven by oscillations of the gravitational quadrupole moment of the secondary, as predicted by the Lanza et al. modification of the Applegate mechanism. Further systematic, long-term monitoring of HU Aqr is required to interpret the (O-C) residuals.

[60]  arXiv:1412.5914 [pdf, ps, other]
Title: Innershell Photoionization Studies of Neutral Atomic Nitrogen
Comments: Submitted to The Astrophysical Journal, 19 pages, 2 tables, and 3 figures
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

Innershell ionization of a $1s$ electron by either photons or electrons is important for X-ray photoionized objects such as active galactic nuclei and electron-ionized sources such as supernova remnants. Modeling and interpreting observations of such objects requires accurate predictions for the charge state distribution (CSD) which results as the $1s$-hole system stabilizes. Due to the complexity of the complete stabilization process, few modern calculations exist and the community currently relies on 40-year-old atomic data. Here, we present a combined experimental and theoretical study for innershell photoionization of neutral atomic nitrogen for photon energies of $403-475$~eV. Results are reported for the total ion yield cross section, for the branching ratios for formation of N$^+$, N$^{2+}$, and N$^{3+}$, and for the average charge state. We find significant differences when comparing to the data currently available to the astrophysics community. For example, while the branching ratio to N$^{2+}$ is somewhat reduced, that for N$^+$ is greatly increased, and that to N$^{3+}$, which was predicted not to be zero, grows to $\approx 10\%$ at the higher photon energies studied. This work demonstrates some of the shortcomings in the theoretical CSD data base for innershell ionization and points the way for the improvements needed to more reliably model the role of innershell ionization of cosmic plasmas.

[61]  arXiv:1412.5916 [pdf, ps, other]
Title: Sub-Megaparsec Individual Photometric Redshift Estimation from Cosmic Web Constraints
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); Instrumentation and Methods for Astrophysics (astro-ph.IM)

We present a method, PhotoWeb, for estimating photometric redshifts of individual galaxies, and their equivalent distance, with megaparsec and even sub-megaparsec accuracy using the Cosmic Web as a constraint over photo-z estimates. PhotoWeb redshift errors for individual galaxies are of the order of delta_z = 0.0007, compared to errors of delta_z = 0.02 for current photo-z techniques. The mean redshift error is of the order of 0.00005-0.0004 compared to mean errors in the range delta_z =z 0.001-0.01 for the best available photo-z estimates in the literature. Current photo-z techniques based on the spectral energy distribution of galaxies and projected clustering produce redshift estimates with large errors due to the poor constraining power the galaxy's spectral energy distribution and projected clustering can provide. The Cosmic Web, on the other hand, provides the strongest constraints on the position of galaxies. The network of walls, filaments and voids occupy ~%10 of the volume of the Universe, yet they contain ~%95 of galaxies. The cosmic web, being a cellular system with well-defined boundaries, sets a restricted set of intermittent positions a galaxy can occupy along a given line-of-sight. Using the information in the density field computed from spectroscopic redshifts we can narrow the possible locations of a given galaxy along the line of sight from a single broad probability distribution (from photo-z) to one or a few narrow peaks. Our first results improve previous photo-z errors by more than one order of magnitude allowing sub-megaparsec errors in some cases. Such accurate estimates for tens of millions of galaxies will allow unprecedented galaxy-LSS studies. In this work we apply our technique to the SDSS photo-z galaxy sample and discuss its performance and future improvements.

[62]  arXiv:1412.5930 [pdf, other]
Title: Do Dark Matter Axions Form a Condensate with Long-Range Correlation?
Comments: 12 double column pages, 1 figure
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)

Recently there has been significant interest in the claim that dark matter axions gravitationally thermalize and form a Bose-Einstein condensate with cosmologically long-range correlation. This has potential consequences for galactic scale observations. Here we critically examine this claim. We point out that there is an essential difference between the thermalization and formation of a condensate due to repulsive interactions, which can indeed drive long-range order, and that due to attractive interactions, which can lead to localized Bose clumps (stars or solitons) that only exhibit short range correlation. While the difference between repulsion and attraction is not present in the standard collisional Boltzmann equation, we argue that it is essential to the field theory dynamics, and we explain why the latter analysis is appropriate for a condensate. Since the axion is primarily governed by attractive interactions -- gravitation and scalar-scalar contact interactions -- we conclude that the claim of long-range correlation is unjustified.

[63]  arXiv:1412.5938 [pdf, other]
Title: A semi-coherent search for weak pulsations in Aql X-1
Comments: 15 pages, 7 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc)

Non pulsating neutron stars in low mass X-ray binaries largely outnumber those that show pulsations. The lack of detectable pulses represents a big open problem for two important reasons. The first is that the structure of the accretion flow in the region closest to the neutron star is not well understood and it is therefore unclear what is the mechanism that prevents the pulse formation. The second is that the detection of pulsations would immediately reveal the spin of the neutron star. Aql X-1 is a special source among low mass X-ray binaries because it has showed the unique property of pulsating for only ~150 seconds out of a total observing time of more than 1.5 million seconds. However, the existing upper limits on the pulsed fraction leave open two alternatives. Either Aql X-1 has very weak pulses which have been undetected, or it has genuinely pulsed only for a tiny amount of the observed time. Understanding which of the two scenarios is the correct one is fundamental to increase our knowledge about the pulse formation process and understand the chances we have to detect weak pulses in other LMXBs. In this paper we perform a semi-coherent search on the entire X-ray data available for Aql X-1. We find no evidence for (new) weak pulsations with the most stringent upper limits being of the order of 0.3% in the 7-25 keV energy band.

[64]  arXiv:1412.5940 [pdf, ps, other]
Title: Cluster Radio Halos at the crossroads between astrophysics and cosmology in the SKA era
Comments: 13 pages, 6 figures, to appear in proceedings of "Advancing Astrophysics with the Square Kilometre Array" PoS(AASKA14)073
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Giant Radio Halos (RH) are diffuse, Mpc-sized, synchrotron radio sources observed in a fraction of merging galaxy clusters. The current scenario for the origin of RHs assumes that turbulence generated during cluster mergers re-accelerates pre-existing fossil and/or secondary electrons in the intra-cluster-medium (ICM) to the energies necessary to produce the observed radio emission. Moreover, more relaxed clusters could host diffuse "off state" halos produced by secondary electrons. In this Chapter we use Monte Carlo simulations, that combine turbulent-acceleration physics and the generation of secondaries in the ICM, to calculate the occurrence of RHs in the Universe, their spectral properties and connection with properties of the hosting clusters. Predictions for SKA1 surveys are presented at low (100-300 MHz) and mid (1-2 GHz) frequencies assuming the expected sensitivities and spatial resolutions of SKA1. SKA1 will step into an unexplored territory allowing us to study the formation and evolution of RHs in a totally new range of cluster masses and redshift, allowing firm tests of the current theoretical hypothesis. In particular, the combination of SKA1-LOW and SUR will allow the discovery of ~1000 ultrasteep- spectrum halos and to detect for the very first time "off state" RHs. We expect that at least ~2500 giant RHs will be discovered by SKA1-LOW surveys up to z~0.6. Remarkably these surveys will be sensitive to RHs in a cluster mass range (down to ~10^14 solar masses) and redshifts (up to ~1) that are unexplored by current observations. SKA1 surveys will be highly competitive with present and future SZ-surveys in the detection of high-redshift massive objects.

[65]  arXiv:1412.5942 [pdf, ps, other]
Title: Searches for continuous gravitational waves from nine young supernova remnants
Comments: Science summary available at this http URL
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We describe directed searches for continuous gravitational waves in data from the sixth LIGO science data run. The targets were nine young supernova remnants not associated with pulsars; eight of the remnants are associated with non-pulsing suspected neutron stars. One target's parameters are uncertain enough to warrant two searches, for a total of ten. Each search covered a broad band of frequencies and first and second frequency derivatives for a fixed sky direction. The searches coherently integrated data from the two LIGO interferometers over time spans from 5.3-25.3 days using the matched-filtering F-statistic. We found no credible gravitational-wave signals. We set 95% confidence upper limits as strong (low) as $4\times10^{-25}$ on intrinsic strain, $2\times10^{-7}$ on fiducial ellipticity, and $4\times10^{-5}$ on r-mode amplitude. These beat the indirect limits from energy conservation and are within the range of theoretical predictions for neutron-star ellipticities and r-mode amplitudes.

[66]  arXiv:1412.5948 [pdf, other]
Title: Robustness of cosmic neutrino background detection in the cosmic microwave background
Comments: 18 pages, 7 figures, 3 tables
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

The existence of a cosmic neutrino background can be probed indirectly by CMB experiments, not only by measuring the background density of radiation in the universe, but also by searching for the typical signatures of the fluctuations of free-streaming species in the temperature and polarisation power spectrum. Previous studies have already proposed a rather generic parametrisation of these fluctuations, that could help to discriminate between the signature of ordinary free-streaming neutrinos, or of more exotic dark radiation models. Current data are compatible with standard values of these parameters, which seems to bring further evidence for the existence of a cosmic neutrino background. In this work, we investigate the robustness of this conclusion under various assumptions. We generalise the definition of an effective sound speed and viscosity speed to the case of massive neutrinos or other dark radiation components experiencing a non-relativistic transition. We show that current bounds on these effective parameters do not vary significantly when considering an arbitrary value of the particle mass, or extended cosmological models with a free effective neutrino number, dynamical dark energy or a running of the primordial spectrum tilt. We conclude that it is possible to make a robust statement about the detection of the cosmic neutrino background by CMB experiments.

[67]  arXiv:1412.5965 [pdf, other]
Title: The JCMT Gould Belt Survey: Evidence for radiative heating in Serpens MWC 297 and its influence on local star formation
Comments: 24 pages, 13 figures, 7 tables
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We present SCUBA-2 450\mu m and 850\mu m observations of the Serpens MWC 297 region, part of the JCMT Gould Belt Survey of nearby star-forming regions. Simulations suggest that radiative feedback influences the star-formation process and we investigate observational evidence for this by constructing temperature maps. Maps are derived from the ratio of SCUBA-2 fluxes and a two component model of the JCMT beam for a fixed dust opacity spectral index of beta = 1.8. Within 40 of the B1.5Ve Herbig star MWC 297, the submillimetre fluxes are contaminated by free-free emission with a spectral index of 1.03\pm0.02, consistent with an ultra-compact HII region and polar winds/jets. Contamination accounts for 73\pm5 per cent and 82\pm4 per cent of peak flux at 450\mu m and 850\mu m respectively. The residual thermal disk of the star is almost undetectable at these wavelengths. Young Stellar Objects are confirmed where SCUBA-2 850\mu m clumps identified by the fellwalker algorithm coincide with Spitzer Gould Belt Survey detections. We identify 23 objects and use Tbol to classify nine YSOs with masses 0.09 to 5.1 M\odot. We find two Class 0, one Class 0/I, three Class I and three Class II sources. The mean temperature is 15\pm2K for the nine YSOs and 32\pm4K for the 14 starless clumps. We observe a starless clump with an abnormally high mean temperature of 46\pm2K and conclude that it is radiatively heated by the star MWC 297. Jeans stability provides evidence that radiative heating by the star MWC 297 may be suppressing clump collapse.

[68]  arXiv:1412.5971 [pdf, ps, other]
Title: Very Long Baseline Interferometry with the SKA
Comments: 19 pages SKA-VLBI review paper with 5 figures, to be published in the proceedings of "Advancing Astrophysics with the Square Kilometre Array", PoS(AASKA14)143
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA); High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR)

Adding VLBI capability to the SKA arrays will greatly broaden the science of the SKA, and is feasible within the current specifications. SKA-VLBI can be initially implemented by providing phased-array outputs for SKA1-MID and SKA1-SUR and using these extremely sensitive stations with other radio telescopes, and in SKA2 by realising a distributed configuration providing baselines up to thousands of km, merging it with existing VLBI networks. The motivation for and the possible realization of SKA-VLBI is described in this paper.

[69]  arXiv:1412.5973 [pdf, other]
Title: Resolving primordial physics through correlated signatures
Comments: 18 pages, 5 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We discuss correlations among spectral observables as a new tool for differentiating between models for the primordial perturbation. We show that if generated in the isocurvature sector, a running of the scalar spectral index is correlated with the statistical properties of non-Gaussianities. In particular, we find a large running will inevitably be accompanied by a large running of $f_{\rm NL}$ and enhanced $g_{\rm NL}$, with $g_{\rm NL}\gg f_{\rm NL}^2$. If the tensor to scalar ratio is large, a large negative running must turn positive on smaller scales. Interestingly, the characteristic scale of the transition could potentially distinguish between the inflaton and isocurvature fields.

[70]  arXiv:1412.5978 [pdf, ps, other]
Title: Coronal Properties of the Seyfert 1.9 Galaxy MCG -05-23-016 Determined from Hard X-ray Spectroscopy with NuSTAR
Comments: 7 pages, 2 figures. Accepted for publication in ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Astrophysics of Galaxies (astro-ph.GA)

Measurements of the high-energy cut-off in the coronal continuum of active galactic nuclei have long been elusive for all but a small number of the brightest examples. We present a direct measurement of the cut-off energy in the nuclear continuum of the nearby Seyfert 1.9 galaxy MCG -05-23-016 with unprecedented precision. The high sensitivity of NuSTAR up to 79 keV allows us to clearly disentangle the spectral curvature of the primary continuum from that of its reflection component. Using a simple phenomenological model for the hard X-ray spectrum, we constrain the cut-off energy to $116_{-5}^{+6}$ keV with 90% confidence. Testing for more complex models and nuisance parameters that could potentially influence the measurement, we find that the cut-off is detected robustly. We further use simple Comptonized plasma models to provide independent constraints for both the kinetic temperature of the electrons in the corona and its optical depth. At the 90% confidence level, we find $kT_e=29\pm2$ keV and $\tau_e=1.23\pm0.08$ assuming a slab (disk-like) geometry, and $kT_e=25\pm2$ keV and $\tau_e=3.5\pm0.2$ assuming a spherical geometry. Both geometries are found to fit the data equally well and their two principal physical parameters are correlated in both cases. With the optical depth in the optically thick regime, the data are pushing the currently available theoretical models of the Comptonized plasma to the limits of their validity. Since the spectral features and variability arising from the inner accretion disk have been observed previously in MCG -05-23-016, the inferred high optical depth implies that a spherical or disk-like corona cannot be homogeneous.

[71]  arXiv:1412.5979 [pdf, other]
Title: Gravitational waves in bigravity cosmology
Comments: 21 pages, 15 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)

In this paper we study gravitational wave perturbations in a cosmological setting of bigravity which can reproduce the $\La$CDM background and large scale structure. We show that in general gravitational wave perturbations are unstable and only for very fine tuned initial conditions such a cosmology is viable. We quantify this fine tuning. We argue that similar fine tuning is also required in the scalar sector in order to prevent the tensor instability to be induced by second order scalar perturbations. Finally, we show that due to this power law instability, models of bigravity can lead to a large tensor to scalar ratio even for low scale inflation.

[72]  arXiv:1412.5990 [pdf, other]
Title: Morphological classification of radio sources for galaxy evolution and cosmology with SKA-MID
Comments: to appear as part of 'Continuum Science' in Proceedings 'Advancing Astrophysics with the Square Kilometre Array (AASKA14)'
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

Morphologically classifying radio sources in continuum images with the SKA has the potential to address some of the key questions in cosmology and galaxy evolution. In particular, we may use different classes of radio sources as independent tracers of the dark-matter density field, and thus overcome cosmic variance in measuring large-scale structure, while on the galaxy evolution side we could measure the mechanical feedback from FRII and FRI jets. This work makes use of a \texttt{MeqTrees}-based simulations framework to forecast the ability of the SKA to recover true source morphologies at high redshifts. A suite of high resolution images containing realistic continuum source distributions with different morphologies (FRI, FRII, starburst galaxies) is fed through an SKA Phase 1 simulator, then analysed to determine the sensitivity limits at which the morphologies can still be distinguished. We also explore how changing the antenna distribution affects these results.

[73]  arXiv:1412.5997 [pdf, other]
Title: GAz: A Genetic Algorithm for Photometric Redshift Estimation
Comments: 9 pages, 8 figures
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We present a new approach to the problem of estimating the redshift of galaxies from photometric data. The approach uses a genetic algorithm combined with non-linear regression to model the 2SLAQ LRG data set with SDSS DR7 photometry. The genetic algorithm explores the very large space of high order polynomials while only requiring optimisation of a small number of terms. We find a $\sigma_{\text{rms}}=0.0408\pm 0.0006$ for redshifts in the range $0.4<z< 0.7$. These results are competitive with the current state-of-the-art but can be presented simply as a polynomial which does not require the user to run any code. For other datasets or applications the code has been made available at https://github.com/rbrthogan/GAz.

[74]  arXiv:1412.6006 [pdf, other]
Title: Enhancing Science from Future Space Missions and Planetary Radar with the SKA
Comments: Advancing Astrophysics with the Square Kilometre Array, Sicily, Italy, June 2014
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Earth and Planetary Astrophysics (astro-ph.EP)

Both Phase 1 of the Square Kilometre Array (SKA1) and the full SKA have the potential to dramatically increase the science return from future astrophysics, heliophysics, and especially planetary missions, primarily due to the greater sensitivity (AEFF / TSYS) compared with existing or planned spacecraft tracking facilities. While this is not traditional radio astronomy, it is an opportunity for productive synergy between the large investment in the SKA and the even larger investments in space missions to maximize the total scientific value returned to society. Specific applications include short-term increases in downlink data rate during critical mission phases or spacecraft emergencies, enabling new mission concepts based on small probes with low power and small antennas, high precision angular tracking via VLBI phase referencing using in-beam calibrators, and greater range and signal/noise ratio for bi-static planetary radar observations. Future use of higher frequencies (e.g., 32 GHz and optical) for spacecraft communications will not eliminate the need for high sensitivities at lower frequencies. Many atmospheric probes and any spacecraft using low gain antennas require frequencies below a few GHz. The SKA1 baseline design covers VHF/UHF frequencies appropriate for some planetary atmospheric probes (band 1) as well as the standard 2.3 GHz deep space downlink frequency allocation (band 3). SKA1-MID also covers the most widely used deep space downlink allocation at 8.4 GHz (band 5). Even a 50% deployment of SKA1-MID will still result in a factor of several increase in sensitivity compared to the current 70-m Deep Space Network tracking antennas, along with an advantageous geographic location. The assumptions of a 10X increase in sensitivity and 20X increase in angular resolution for SKA result in a truly unique and spectacular future spacecraft tracking capability.

[75]  arXiv:1412.6023 [pdf, other]
Title: Constraining the intra-cluster pressure profile from the thermal SZ power spectrum
Comments: Submitted to A&A
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

The angular power spectrum of the thermal Sunyaev-Zel'dovich (tSZ) effect is highly sensitive to cosmological parameters such as sigma8 and OmegaM, but its use as a precision cosmological probe is hindered by the astrophysical uncertainties in modeling the gas pressure profile in galaxy groups and clusters. In this paper we assume that the relevant cosmological parameters are accurately known, and explore the ability of current and future tSZ power spectrum measurements to constrain the intra-cluster gas pressure or the evolution of the gas mass fraction, f_gas. We use the CMB bandpower measurements from the South Pole Telescope and a Bayesian MCMC method to quantify deviations from the standard, universal gas pressure model. We explore analytical model extensions that bring the predictions for the tSZ power in agreement with experimental data. We find that a steeper pressure profile in the cluster outskirts or an evolving f_gas have mild to severe conflicts with experimental data or simulations. Varying more than one parameter in the pressure model leads to strong degeneracies that cannot be broken with current observational constraints. We use simulated bandpowers from future tSZ survey experiments, in particular a possible 2000 deg^2 CCAT survey, to show that future observations can provide almost an order of magnitude better precision on the same model parameters. This will allow to break the current parameter degeneracies and place simultaneous constraints on the gas pressure profile and its redshift evolution, for example.

[76]  arXiv:1412.6035 [pdf, ps, other]
Title: Forensics of Subhalo-Stream Encounters: The Three Phases of Gap Growth
Comments: 14 pages and 13 figures. Submitted to MNRAS. Comments welcome! Links to movies of stream gaps in the conclusions
Subjects: Astrophysics of Galaxies (astro-ph.GA)

There is hope to discover dark matter subhalos free of stars (predicted by the current theory of structure formation) by observing gaps they produce in tidal streams. In fact, this is the most promising technique for dark substructure detection and characterization as such gaps grow with time and hence become more observable by ongoing and planned Galaxy surveys. To facilitate such future inference, we develop a comprehensive framework for studies of the growth of the stream density perturbations. Starting with simple assumptions, we derive analytic formulae that describe the evolution of all gap properties (size, density contrast etc) at all times. We uncover complex, previously unnoticed behavior, with the stream initially forming a density enhancement near the subhalo impact point. Shortly after, a gap forms due to the relative change in period induced by the subhalo's passage. There is an intermediate regime where the gap grows linearly in time. At late times, the particles in the stream overtake each other, forming caustics, and the gap grows like $\sqrt{t}$. In addition to the secular growth, we find that the gap oscillates as it grows due to epicyclic motion. We compare this analytic model to N-body simulations and find an impressive level of agreement. Importantly, when analyzing the observation of a single gap we find a large degeneracy between the subhalo mass, the impact geometry and kinematics, the host potential and the time since flyby.

[77]  arXiv:1412.6036 [pdf, ps, other]
Title: Constraint on noncommutative spacetime from PLANCK data
Comments: 7 pages, 4 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We constrain the energy scale of noncommutativity of spacetime using CMB data from PLANCK. We find that PLANCK data puts the lower bound on the noncommutativity energy scale to about 20 TeV, which is about a factor of two larger than a previous constraint that was obtained using data from WMAP, ACBAR and CBI. We further show that inclusion of data of $E$ mode of CMB polarization will not significantly change the constraint.

[78]  arXiv:1412.6040 [pdf, other]
Title: Identifying the first generation of radio powerful AGN in the Universe with the SKA
Authors: Jose Afonso (1,2), Jordi Casanellas (3), Isabella Prandoni (4), Matt Jarvis (5,6), Silvio Lorenzoni (1), Manuela Magliocchetti (7), Nick Seymour (8) ((1) Institute of Astrophysics and Space Sciences, Portugal (2) Faculdade de Ciencias, Universidade de Lisboa (3) Max Planck Institut fur Gravitationsphysik (Albert-Einstein- Institut) (4) INAF - Istituto di Radioastronomia, Bologna (5) Astrophysics, University of Oxford (6) Physics Department, University of the Western Cape (7) INAF-IAPS (8) International Centre for Radio Astronomy Research, Curtin University)
Comments: 10 pages, 2 figures. To appear as part of "Continuum Science" in the Proceedings of "Advancing Astrophysics with the Square Kilometre Array" PoS(AASKA14)071
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

One of the most challenging and exciting subjects in modern astrophysics is that of galaxy formation at the epoch of reionisation. The SKA, with its revolutionary capabilities in terms of frequency range, resolution and sensitivity, will allow to explore the first Gyr of structure formation in the Universe, in particular, with the detection and study of the earliest manifestations of the AGN phenomenon. The tens of QSOs that are currently known out to the highest redshifts (z~7), many of them exhibiting powerful radio emission, imply that super-massive black holes can be grown on a very short timescale and support the existence of very high redshift (z > 7) radio loud sources - sources that have so far escaped detection. Not only would such detections be paramount to the understanding of the earliest stages of galaxy evolution, they are necessary for the direct study of neutral hydrogen in the Epoch of Reionisation, through observations of the HI 21cm forest against such background sources. In order to understand how SKA and SKA1 observations can be optimised to reveal these earliest AGN, we have examined the effect of a hot CMB on the emission of powerful and young radio galaxies. By looking at the SKA1 capabilities, in particular in terms of wavelength coverage and resolution, we determine how the effects of "CMB-muting" of a radio loud source can be observationally minimised and how to identify the best highest-redshift radio candidates. Considering different predictions for the space density of radio loud AGN at such redshifts, we identify the survey characteristics necessary to optimize the detection and identification of the very first generation of radio loud AGN in the Universe.

[79]  arXiv:1412.6051 [pdf, ps, other]
Title: Dissecting the thermal Sunyaev-Zeldovich-gravitational lensing cross-correlation with hydrodynamical simulations
Comments: 9 pages, 4 figures, 3 tables
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We use the cosmo-OWLS suite of cosmological hydrodynamical simulations, which includes different galactic feedback models, to predict the cross-correlation signal between weak gravitational lensing and the thermal Sunyaev-Zeldovich (tSZ) $y$-parameter. The predictions are compared to the recent detection reported by van Waerbeke and collaborators. The simulations reproduce the weak lensing-tSZ cross-correlation, $\xi_{y\kappa}(\theta)$, well. The uncertainty arising from different possible feedback models appears to be important on small scales only ($\theta \lesssim 10$ arcmin), while the amplitude of the correlation on all scales is sensitive to cosmological parameters that control the growth rate of structure (such as $\sigma_8$, $\Omega_m$ and $\Omega_b$). This study confirms our previous claim (in Ma et al.) that a significant proportion of the signal originates from the diffuse gas component in low-mass ($M_{\rm{halo}} \lesssim 10^{14} M_{\odot}$) clusters as well as from the region beyond the virial radius. We estimate that approximately 20$\%$ of the detected signal comes from low-mass clusters, which corresponds to about 30$\%$ of the baryon density of the Universe. The simulations also suggest that more than half of the baryons in the Universe are in the form of diffuse gas outside halos ($\gtrsim 5$ times the virial radius) which is not hot or dense enough to produce a significant tSZ signal or be observed by X-ray experiments. Finally, we show that future high-resolution tSZ-lensing cross-correlation observations will serve as a powerful tool for discriminating between different galactic feedback models.

[80]  arXiv:1412.6076 [pdf, ps, other]
Title: The SKA Mid-frequency All-sky Continuum Survey: Discovering the unexpected and transforming radio-astronomy
Comments: to appear as part of 'Continuum Science' in Proceedings 'Advancing Astrophysics with the SKA (AASKA14)'
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

We show that, in addition to specific science goals, there is a strong case for conducting an all-sky (i.e. the visible 3-pi steradians) SKA continuum survey which does not fit neatly into conventional science cases. History shows that the greatest scientific impact of most major telescopes (e.g., HST, VLA) lies beyond the original goals used to justify the telescope. The design of the telescope therefore needs to maximise the ultimate scientific productivity, in addition to achieving the specific science goals. In this chapter, we show that an all-sky continuum survey is likely to achieve transformational science in two specific respects: (1) Discovering the unexpected (2) Transforming radio-astronomy from niche to mainstream

[81]  arXiv:1412.6090 [pdf, ps, other]
Title: The evolution of the cold interstellar medium in galaxies following a starburst
Comments: 22 pages including 4 pages of appendices, 14 figures, 4 tables. Accepted for publication in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present the evolution of dust and molecular gas properties in a sample of 11 $z\sim0.03$ starburst to post-starburst (PSB) galaxies selected to span an age sequence from ongoing starburst to 1 Gyr after the starburst ended. All PSBs harbour significant molecular gas and dust reservoirs and residual star formation, indicating that complete quenching of the starburst due to exhaustion or expulsion of gas has not occurred during this timespan. As the starburst ages, we observe a clear decrease in the star-formation efficiency, molecular gas and SFR surface density, and effective dust temperature, from levels coincident with starburst galaxies to those of normal star-forming galaxies. These trends are consistent with a natural decrease in the SFR following consumption of molecular gas by the starburst, and corresponding decrease in the interstellar radiation field strength as the starburst ages. The gas and dust contents of the PSBs are coincident with those of star-forming galaxies and molecular gas-rich early-type galaxies, and are not consistent with galaxies on the red-sequence. We find no evidence that the global gas reservoir is expelled by stellar winds or AGN feedback. Our results show that although a strong starburst in a low-redshift galaxy may cause the galaxy to ultimately have a lower specific SFR and be of an earlier morphological type, the galaxy will remain in the "green valley" for an extended time. Multiple such episodes may be needed to complete migration of the galaxy from the blue- to red-sequence.

[82]  arXiv:1412.6091 [pdf, other]
Title: Nuclear structure aspects of spin-independent WIMP scattering off xenon
Comments: 10 pages, 24 figures
Subjects: Nuclear Theory (nucl-th); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph)

We study the structure factors for spin-independent WIMP scattering off xenon based on state-of-the-art large-scale shell-model calculations, which are shown to yield a good spectroscopic description of all experimentally relevant isotopes. Our results are based on the leading scalar one-body currents only. At this level and for the momentum transfers relevant to direct dark matter detection, the structure factors are in very good agreement with the phenomenological Helm form factors used to give experimental limits for WIMP-nucleon cross sections. In contrast to spin-dependent WIMP scattering, the spin-independent channel, at the one-body level, is less sensitive to nuclear structure details. In addition, we explicitly show that the structure factors for inelastic scattering are suppressed by ~ 10^{-4} compared to the coherent elastic scattering response. This implies that the detection of inelastic scattering will be able to discriminate clearly between spin-independent and spin-dependent scattering. Finally, we provide fits for all calculated structure factors.