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[1]  arXiv:1407.8178 [pdf, other]
Title: Velocity anti-correlation of diametrically opposed galaxy satellites in the low redshift universe
Comments: Nature in press
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Recent work has shown that both the Milky Way and the Andromeda galaxies possess the unexpected property that their dwarf satellite galaxies are aligned in thin and kinematically coherent planar structures. It is now important to evaluate the incidence of such planar structures in the larger galactic population, since the Local Group may not be a sufficiently representative environment. Here we report that the measurement of the velocity of pairs of diametrically opposed galaxy satellites provides a means to determine statistically the prevalence of kinematically coherent planar alignments. In the local universe (redshift $z<0.05$), we find that such satellite pairs out to a galactocentric distance of $150$ kpc are preferentially anti-correlated in their velocities (99.994% confidence level), and that the distribution of galaxies in the larger scale environment (beyond 150 kpc and up to $\approx 2$ Mpc) is strongly elongated along the axis joining the inner satellite pair ($>7\sigma$ confidence). Our finding may indicate that co-rotating planes of satellites, similar to that seen around the Andromeda galaxy, are ubiquitous in nature, while their coherent motion also suggests that they are a significant repository of angular momentum on $\sim 100$ kpc scales.

[2]  arXiv:1407.8179 [pdf, other]
Title: High-efficiency Autonomous Laser Adaptive Optics
Comments: Published in ApJL. 6 pages, 4 figures, and 1 table
Journal-ref: The Astrophysical Journal Letters, 2014, Volume 790, Issue 1, article id. L8
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

As new large-scale astronomical surveys greatly increase the number of objects targeted and discoveries made, the requirement for efficient follow-up observations is crucial. Adaptive optics imaging, which compensates for the image-blurring effects of Earth's turbulent atmosphere, is essential for these surveys, but the scarcity, complexity and high demand of current systems limits their availability for following up large numbers of targets. To address this need, we have engineered and implemented Robo-AO, a fully autonomous laser adaptive optics and imaging system that routinely images over 200 objects per night with an acuity 10 times sharper at visible wavelengths than typically possible from the ground. By greatly improving the angular resolution, sensitivity, and efficiency of 1-3 m class telescopes, we have eliminated a major obstacle in the follow-up of the discoveries from current and future large astronomical surveys.

[3]  arXiv:1407.8180 [pdf, ps, other]
Title: Radio Observations of GRB Host Galaxies
Authors: E R Stanway (Warwick, UK), A J Levan (Warwick, UK), Luke J M Davies (ICRAR, Australia)
Comments: 15 pages, MNRAS accepted
Subjects: Astrophysics of Galaxies (astro-ph.GA); High Energy Astrophysical Phenomena (astro-ph.HE)

We present 5.5 and 9.0 GHz observations of a sample of seventeen GRB host galaxies at 0.5<z<1.4, using the radio continuum to explore their star formation properties in the context of the small but growing sample of galaxies with similar observations. Four sources are detected, one of those (GRB 100418A) likely due to lingering afterglow emission. We suggest that the previously-reported radio afterglow of GRB 100621A may instead be due to host galaxy flux. We see no strong evidence for redshift evolution in the typical star formation rate of GRB hosts, but note that the fraction of `dark' bursts with detections is higher than would be expected given constraints on the more typical long GRB population. We also determine the average radio-derived star formation rates of core collapse supernovae at comparable redshift, and show that these are still well below the limits obtained for GRB hosts, and show evidence for a rise in typical star formation rate with redshift in supernova hosts.

[4]  arXiv:1407.8181 [pdf, other]
Title: X-ray bright active galactic nuclei in massive galaxy clusters III: New insights into the triggering mechanisms of cluster AGN
Comments: 21 Pages, 8 figures, 5 tables. Submitted to MNRAS. Comments are welcome, and please request Steven Ehlert for higher resolution figures
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We present the results of a new analysis of the X-ray selected Active Galactic Nuclei (AGN) population in the vicinity of 135 of the most massive galaxy clusters in the redshift range of 0.2 < z < 0.9 observed with Chandra. With a sample of more than 11,000 X-ray point sources, we are able to measure, for the first time, evidence for evolution in the cluster AGN population beyond the expected evolution of field AGN. Our analysis shows that overall number density of cluster AGN scales with the cluster mass as $\sim M_{500}^{-1.2}$. There is no evidence for the overall number density of cluster member X-ray AGN depending on the cluster redshift in a manner different than field AGN, nor there is any evidence that the spatial distribution of cluster AGN (given in units of the cluster overdensity radius r_500) strongly depends on the cluster mass or redshift. The $M^{-1.2 \pm 0.7}$ scaling relation we measure is consistent with theoretical predictions of the galaxy merger rate in clusters, which is expected to scale with the cluster velocity dispersion, $\sigma$, as $ \sim \sigma^{-3}$ or $\sim M^{-1}$. This consistency suggests that AGN in clusters may be predominantly triggered by galaxy mergers, a result that is further corroborated by visual inspection of Hubble images for 23 spectroscopically confirmed cluster member AGN in our sample. A merger-driven scenario for the triggering of X-ray AGN is not strongly favored by studies of field galaxies, however, suggesting that different mechanisms may be primarily responsible for the triggering of cluster and field X-ray AGN.

[5]  arXiv:1407.8184 [pdf, ps, other]
Title: Are Scalar and Tensor Deviations Related in Modified Gravity?
Authors: Eric V. Linder
Comments: 6 pages, 3 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)

Modified gravity theories on cosmic scales have three key deviations from general relativity. They can cause cosmic acceleration without a physical, highly negative pressure fluid, can cause a gravitational slip between the two metric potentials, and can cause gravitational waves to propagate differently, e.g. with a speed different from the speed of light. We examine whether the deviations in the metric potentials as observable through modified Poisson equations for scalar density perturbations are related to or independent from deviations in the tensor gravitational waves. We show analytically they are independent instantaneously in covariant Galileon gravity -- e.g. at some time one of them can have the general relativity value while the other deviates -- though related globally -- if one deviates over a finite period, the other at some point shows a deviation. We present expressions for the early time and late time de Sitter limits, and numerically illustrate their full evolution. This in(ter)dependence of the scalar and tensor deviations highlights complementarity between cosmic structure surveys and future gravitational wave measurements.

[6]  arXiv:1407.8185 [pdf, ps, other]
Title: The role of major mergers in the size growth of intermediate-mass spheroids
Comments: MNRAS in press
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We study of the role of major mergers (mass ratios >1:4) in driving size growth in high-redshift (1<z<2) spheroidal galaxies (SGs) with stellar masses between 10^9.5 MSun and 10^10.7 MSun. This is a largely unexplored mass range at this epoch, containing the progenitors of more massive SGs on which the bulk of the size-evolution literature is based. We visually split our SGs into systems that are relaxed and those that exhibit tidal features indicative of a recent merger. Numerical simulations indicate that, given the depth of our images, only tidal features due to major mergers will be detectable at these epochs (features from minor mergers being too faint), making the disturbed SGs a useful route for estimating major-merger-driven size growth. The disturbed SGs are offset in size from their relaxed counterparts, lying close to the upper envelope of the local size -- mass relation. The mean size ratio of the disturbed SGs to their relaxed counterparts is ~2. Combining this observed size growth with empirical major-merger histories from the literature suggests that the size evolution of a significant fraction (around two-thirds) of SGs in this mass range could be driven by major mergers. If, as is likely, our galaxies are progenitors of more massive M > 10^10.7 MSun SGs at z<1, then major mergers are also likely to play an important role in the size growth of at least some massive SGs in this mass range.

[7]  arXiv:1407.8189 [pdf, ps, other]
Title: Nonlinear evolution of dark matter subhalos and applications to warm dark matter
Comments: 10 pages, 9 figures, accepted for publication in the Astrophysical Journal
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We describe the methodology to include nonlinear evolution, including tidal effects, in the computation of subhalo distribution properties in both cold (CDM) and warm (WDM) dark matter universes. Using semi-analytic modeling, we include effects from dynamical friction, tidal stripping, and tidal heating, allowing us to dynamically evolve the subhalo distribution. We calibrate our nonlinear evolution scheme to the CDM subhalo mass function in the Aquarius N-body simulation, producing a subhalo mass function within the range of simulations. We find tidal effects to be the dominant mechanism of nonlinear evolution in the subhalo population. Finally, we compute the subhalo mass function for $m_\chi=1.5$ keV WDM including the effects of nonlinear evolution, and compare radial number densities and mass density profiles of subhalos in CDM and WDM models. We show that all three signatures differ between the two dark matter models, suggesting that probes of substructure may be able to differentiate between them.

[8]  arXiv:1407.8190 [pdf, ps, other]
Title: Study of the sub-AU disk of the Herbig B[e] star HD 85567 with near-infrared interferometry
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Context: The structure of the inner disk of Herbig Be stars is not well understood. The continuum disks of several Herbig Be stars have inner radii that are smaller than predicted by models of irradiated disks with optically thin holes.
Aims: We study the size of the inner disk of the Herbig B[e] star HD 85567 and compare the model radii with the radius suggested by the size-luminosity relation.
Methods: The object was observed with the AMBER instrument of the Very Large Telescope Interferometer. We obtained K-band visibilities and closure phases. These measurements are interpreted with geometric models and temperature-gradient models.
Results: Using several types of geometric star-disk and star-disk-halo models, we derived inner ring-fit radii in the K band that are in the range of 0.8 - 1.6 AU. Additional temperature-gradient modeling resulted in an extended disk with an inner radius of $0.67^{+0.51}_{-0.21}$ AU, a high inner temperature of $2200^{+750}_{-350}$ K, and a disk inclination of $53^{+15}_{-11}$$^\circ$.
Conclusions: The derived geometric ring-fit radii are approximately 3 - 5 times smaller than that predicted by the size-luminosity relation. The small geometric and temperature-gradient radii suggest optically thick gaseous material that absorbs stellar radiation inside the dust disk.

[9]  arXiv:1407.8192 [pdf, other]
Title: Testing primordial non-Gaussianities on galactic scales at high redshift
Comments: 6 pages, 3 figures, 1 table, submitted to MNRAS
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA)

The simplest inflationary models predict a very nearly Gaussian distribution of density fluctuations. Primordial non-Gaussianities therefore provide an important test of inflationary models. Although the Planck CMB experiment has produced strong limits on non-Gaussianity on scales of clusters, there is still room for considerable non-Gaussianity on galactic scales. We have tested the effect of local non-Gaussianity on the high redshift galaxy population by running five cosmological N-body simulations down to z=6.5. For these simulations, we adopt the same initial phases, and either Gaussian or scale-dependent non-Gaussian primordial fluctuations, all consistent with the constraints set by Planck on clusters scales. We then assign stellar masses to each halo using the halo - stellar mass empirical relation of Behroozi et al. (2013). Our simulations with non-Gaussian initial conditions produce halo mass functions that show clear departures from those obtained from the analogous simulations with Gaussian initial conditions at z>~10. We observe a >0.3 dex boosting of the low-end of the halo mass function, which leads to a similar effect on the galaxy stellar mass function, which should be testable with future galaxy surveys at z>10. As cosmic reionization is thought to be driven by dwarf galaxies at high redshift, our findings may have implications for the reionization history of the Universe.

[10]  arXiv:1407.8204 [pdf, other]
Title: Inflationary tensor fossils in large-scale structure
Comments: 27 pages, 3 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)

Inflation models make specific predictions for a tensor-scalar-scalar three-point correlation, or bispectrum, between one gravitational-wave (tensor) mode and two density-perturbation (scalar) modes. This tensor-scalar-scalar correlation leads to a local power quadrupole, an apparent departure from statistical isotropy in our Universe, as well as characteristic four-point correlations in the current mass distribution in the Universe. So far, the predictions for these observables have been worked out only for single-clock models in which certain consistency conditions between the tensor-scalar-scalar correlation and tensor and scalar power spectra are satisfied. Here we review the requirements on inflation models for these consistency conditions to be satisfied. We then consider several examples of inflation models, such as non-attractor and solid inflation models, in which these conditions are put to the test. In solid inflation the simplest consistency conditions are already violated whilst in the non-attractor model we find that, contrary to the standard scenario, the tensor-scalar-scalar correlator probes directly relevant model-dependent information. We work out the predictions for observables in these models. For non-attractor inflation we find an apparent local quadrupolar departure from statistical isotropy in large-scale structure but that this power quadrupole decreases very rapidly at smaller scales. The consistency of the CMB quadrupole with statistical isotropy then constrains the distance scale that corresponds to the transition from the non-attractor to attractor phase of inflation to be larger than the currently observable horizon. Solid inflation predicts clustering fossils signatures in the current galaxy distribution that may be large enough to be detectable with forthcoming, and possibly even current, galaxy surveys.

[11]  arXiv:1407.8205 [pdf, other]
Title: Commissioning ShARCS: the Shane Adaptive optics infraRed Camera-Spectrograph for the Lick Observatory 3-m telescope
Comments: 9 pages, 7 figures. Presented at SPIE Astronomical Telescopes + Instrumentation conference, paper 9148-118
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

We describe the design and first-light early science performance of the Shane Adaptive optics infraRed Camera-Spectrograph (ShARCS) on Lick Observatory's 3-m Shane telescope. Designed to work with the new ShaneAO adaptive optics system, ShARCS is capable of high-efficiency, diffraction-limited imaging and low-dispersion grism spectroscopy in J, H, and K-bands. ShARCS uses a HAWAII-2RG infrared detector, giving high quantum efficiency (>80%) and Nyquist sampling the diffraction limit in all three wavelength bands. The ShARCS instrument is also equipped for linear polarimetry and is sensitive down to 650 nm to support future visible-light adaptive optics capability. We report on the early science data taken during commissioning.

[12]  arXiv:1407.8206 [pdf, other]
Title: Swimming with ShARCS: Comparison of On-sky Sensitivity With Model Predictions for ShaneAO on the Lick Observatory 3-meter Telescope
Comments: 13 pages, 5 figures, SPIE Astronomical Telescopes + Instrumentation, Montreal 2014
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

The Lick Observatory's Shane 3-meter telescope has been upgraded with a new infrared instrument (ShARCS - Shane Adaptive optics infraRed Camera and Spectrograph) and dual-deformable mirror adaptive optics (AO) system (ShaneAO). We present first-light measurements of imaging sensitivity in the Ks band. We compare measured results to predicted signal-to-noise ratio and magnitude limits from modeling the emissivity and throughput of ShaneAO and ShARCS. The model was validated by comparing its results to the Keck telescope adaptive optics system model and then by estimating the sky background and limiting magnitudes for IRCAL, the previous infra-red detector on the Shane telescope, and comparing to measured, published results. We predict that the ShaneAO system will measure lower sky backgrounds and achieve 20\% higher throughput across the $JHK$ bands despite having more optical surfaces than the current system. It will enable imaging of fainter objects (by 1-2 magnitudes) and will be faster to reach a fiducial signal-to-noise ratio by a factor of 10-13. We highlight the improvements in performance over the previous AO system and its camera, IRCAL.

[13]  arXiv:1407.8207 [pdf, other]
Title: ShaneAO: wide science spectrum adaptive optics system for the Lick Observatory
Comments: 11 pages, 10 figures. Presented at SPIE Astronomical Telescopes + Instrumentation conference, paper 9148-76
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

A new high-order adaptive optics system is now being commissioned at the Lick Observatory Shane 3-meter telescope in California. This system uses a high return efficiency sodium beacon and a combination of low and high-order deformable mirrors to achieve diffraction-limited imaging over a wide spectrum of infrared science wavelengths covering 0.8 to 2.2 microns. We present the design performance goals and the first on-sky test results. We discuss several innovations that make this system a pathfinder for next generation AO systems. These include a unique woofer-tweeter control that provides full dynamic range correction from tip/tilt to 16 cycles, variable pupil sampling wavefront sensor, new enhanced silver coatings developed at UC Observatories that improve science and LGS throughput, and tight mechanical rigidity that enables a multi-hour diffraction- limited exposure in LGS mode for faint object spectroscopy science.

[14]  arXiv:1407.8208 [pdf, other]
Title: Woofer-tweeter deformable mirror control for closed-loop adaptive optics: theory and practice
Comments: 11 pages, 4 figures, Presented SPIE Astronomical Telescopes and Instrumentation Conference, paper #9148-174
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

Deformable mirrors with very high order correction generally have smaller dynamic range of motion than what is required to correct seeing over large aperture telescopes. As a result, systems will need to have an architecture that employs two deformable mirrors in series, one for the low-order but large excursion parts of the wavefront and one for the finer and smaller excursion components. The closed-loop control challenge is to a) keep the overall system stable, b) avoid the two mirrors using control energy to cancel each other's correction, c) resolve actuator saturations stably, d) assure that on average the mirrors are each correcting their assigned region of spatial frequency space. We present the control architecture and techniques for assuring that it is linear and stable according to the above criteria. We derived the analytic forms for stability and performance and show results from simulations and on-sky testing using the new ShaneAO system on the Lick 3-meter telescope.

[15]  arXiv:1407.8209 [pdf]
Title: Opto-Mechanical Design of ShaneAO: the Adaptive Optics System for the 3-meter Shane Telescope
Comments: 14 pages, 14 figures, 4 tables. Presented at SPIE Astronomical Telescopes + Instrumentation conference, paper 9148-119
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

A Cassegrain mounted adaptive optics instrument presents unique challenges for opto-mechanical design. The flexure and temperature tolerances for stability are tighter than those of seeing limited instruments. This criteria requires particular attention to material properties and mounting techniques. This paper addresses the mechanical designs developed to meet the optical functional requirements. One of the key considerations was to have gravitational deformations, which vary with telescope orientation, stay within the optical error budget, or ensure that we can compensate with a steering mirror by maintaining predictable elastic behavior. Here we look at several cases where deformation is predicted with finite element analysis and Hertzian deformation analysis and also tested. Techniques used to address thermal deformation compensation without the use of low CTE materials will also be discussed.

[16]  arXiv:1407.8211 [pdf]
Title: Misaligned Protoplanetary Disks in a Young Binary System
Comments: Published in Nature, July 31 2014. 18 pages. This version has slight differences from the final published version. Final version is available at this http URL
Journal-ref: Nature 511, 567-569 (31 July 2014)
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)

Many extrasolar planets follow orbits that differ from the nearly coplanar and circular orbits found in our solar system; orbits may be eccentric or inclined with respect to the host star's equator, and the population of giant planets orbiting close to their host stars suggests significant orbital migration. There is currently no consensus on what produces such orbits. Theoretical explanations often invoke interactions with a binary companion star on an orbit that is inclined relative to the planet's orbital plane. Such mechanisms require significant mutual inclinations between planetary and binary star orbital planes. The protoplanetary disks in a few young binaries are misaligned, but these measurements are sensitive only to a small portion of the inner disk, and the three-dimensional misalignment of the bulk of the planet-forming disk mass has hitherto not been determined. Here we report that the protoplanetary disks in the young binary system HK Tau are misaligned by 60{\deg}-68{\deg}, so one or both disks are significantly inclined to the binary orbital plane. Our results demonstrate that the necessary conditions exist for misalignment-driven mechanisms to modify planetary orbits, and that these conditions are present at the time of planet formation, apparently due to the binary formation process.

[17]  arXiv:1407.8212 [pdf, ps, other]
Title: Early evolution of the extraordinary Nova Del 2013 (V339 Del)
Comments: 14 pages, 9 figures, 3 tables, accepted for Astronomy and Astrophysics
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We determine the temporal evolution of the luminosity L(WD), radius R(WD) and effective temperature Teff of the white dwarf (WD) pseudophotosphere of V339 Del from its discovery to around day 40. Another main objective was studying the ionization structure of the ejecta. These aims were achieved by modelling the optical/near-IR spectral energy distribution (SED) using low-resolution spectroscopy (3500 - 9200 A), UBVRcIc and JHKLM photometry. During the fireball stage (Aug. 14.8 - 19.9, 2013), Teff was in the range of 6000 - 12000 K, R(WD) was expanding non-uniformly in time from around 66 to around 300 (d/3 kpc) R(Sun), and L(WD) was super-Eddington, but not constant. After the fireball stage, a large emission measure of 1.0-2.0E+62 (d/3 kpc)**2 cm**(-3) constrained the lower limit of L(WD) to be well above the super-Eddington value. The evolution of the H-alpha line and mainly the transient emergence of the Raman-scattered O VI 1032 A line suggested a biconical ionization structure of the ejecta with a disk-like H I region persisting around the WD until its total ionization, around day 40. It is evident that the nova was not evolving according to the current theoretical prediction. The unusual non-spherically symmetric ejecta of nova V339 Del and its extreme physical conditions and evolution during and after the fireball stage represent interesting new challenges for the theoretical modelling of the nova phenomenon.

[18]  arXiv:1407.8214 [pdf, ps, other]
Title: The evolution of galaxy star formation activity in massive halos
Comments: 14 pages, 10 figures, submitted to A&A
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

There is now a large consensus that the current epoch of the Cosmic Star Formation History (CSFH) is dominated by low mass galaxies while the most active phase at 1<z<2 is dominated by more massive galaxies, which undergo a faster evolution. Massive galaxies tend to inhabit very massive halos such as galaxy groups and clusters. We aim to understand whether the observed "galaxy downsizing" could be interpreted as a "halo downsizing", whereas the most massive halos, and their galaxy populations, evolve more rapidly than the halos of lower mass. Thus, we study the contribution to the CSFH of galaxies inhabiting group-sized halos. This is done through the study of the evolution of the Infra-Red (IR) luminosity function of group galaxies from redshift 0 to ~1.6. We use a sample of 39 X-ray selected groups in the Extended Chandra Deep Field South (ECDFS), the Chandra Deep Field North (CDFN), and the COSMOS field, where the deepest available mid- and far-IR surveys have been conducted with Spitzer MIPS and Hersche PACS. Groups at low redshift lack the brightest, rarest, and most star forming IR-emitting galaxies observed in the field. Their IR-emitting galaxies contribute <10% of the comoving volume density of the whole IR galaxy population in the local Universe. At redshift >~1, the most IR-luminous galaxies (LIRGs and ULIRGs) are preferentially located in groups, and this is consistent with a reversal of the star-formation rate vs .density anti-correlation observed in the nearby Universe. At these redshifts, group galaxies contribute 60-80% of the CSFH, i.e. much more than at lower redshifts. Below z~1, the comoving number and SFR densities of IR-emitting galaxies in groups decline significantly faster than those of all IR-emitting galaxies. Our results are consistent with a "halo downsizing" scenario and highlight the significant role of "environment" quenching in shaping the CSFH.

[19]  arXiv:1407.8223 [pdf, ps, other]
Title: The NuSTAR spectrum of Mrk 335: Extreme relativistic effects within 2 gravitational radii of the event horizon?
Comments: Accepted for publication in MNRAS
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We present 3-50 keV NuSTAR observations of the AGN Mrk 335 in a very low flux state. The spectrum is dominated by very strong features at the energies of the iron line at 5-7 keV and Compton hump from 10-30 keV. The source is variable during the observation, with the variability concentrated at low energies, which suggesting either a relativistic reflection or a variable absorption scenario. In this work we focus on the reflection interpretation, making use of new relativistic reflection models that self consistently calculate the reflection fraction, relativistic blurring and angle-dependent reflection spectrum for different coronal heights to model the spectra. We find that the spectra can be well fit with relativistic reflection, and that the lowest flux state spectrum is described by reflection alone, suggesting the effects of extreme light-bending occurring within ~2 gravitational radii of the event horizon. The reflection fraction decreases sharply with increasing flux, consistent with a point source moving up to above 10 Rg as the source brightens. We constrain the spin parameter to greater than 0.9 at the 3 sigma confidence level. By adding a spin-dependent upper limit on the reflection fraction to our models, we demonstrate that this can be a powerful way of constraining the spin parameter, particularly in reflection dominated states. We also calculate a detailed emissivity profile for the iron line, and find that it closely matches theoretical predictions for a compact source within a few Rg of the black hole.

[20]  arXiv:1407.8228 [pdf, ps, other]
Title: Grain Alignment by Radiative Torques in Special Conditions and Implications
Comments: 26 pages, 15 figures, published in MNRAS
Journal-ref: MNRAS 438, 680-703 (2014)
Subjects: Astrophysics of Galaxies (astro-ph.GA); Earth and Planetary Astrophysics (astro-ph.EP)

Grain alignment by radiative torques (RATs) has been extensively studied for various environment conditions, including interstellar medium, dense molecular clouds, and accretion disks, thanks to significant progress in observational, theoretical and numerical studies. In this paper, we explore the alignment by RATs and provide quantitative predictions of dust polarization for a set of astrophysical environments that can be tested observationally. We first consider the alignment of grains in the local interstellar medium and compare predictions for linear polarization by aligned grains with recent observational data for nearby stars. We then revisit the problem of grain alignment in accretions disks by taking into account the dependence of RAT alignment efficiency on the anisotropic direction of radiation fields relative to magnetic fields. Moreover, we study the grain alignment in interplanetary medium, including diffuse Zodiacal cloud and cometary comae, and calculate the degree of circular polarization (CP) of scattered light arising from single scattering by aligned grains. We also discuss a new type of grain alignment, namely the alignment with respect to the ambient electric field instead of the alignment with the magnetic field. We show that this type of alignment can allow us to reproduce the systematic features of CP observed across a cometary coma. Our findings suggest that polarized Zodiacal dust emission may be an important polarized foreground component, which should be treated carefully in cosmic microwave background experiments.

[21]  arXiv:1407.8230 [pdf, other]
Title: On the Clustering of Compact Galaxy Pairs in Dark Matter Haloes
Comments: Accepted by MNRAS, 17 pages, 12 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We analyze the clustering of photometrically selected galaxy pairs by using the halo-occupation distribution (HOD) model. We measure the angular two-point auto-correlation function, $\omega(\theta)$, for galaxies and galaxy pairs in three volume-limited samples and develop an HOD to model their clustering. Our results are successfully fit by these HOD models, and we see the separation of "1-halo" and "2-halo" clustering terms for both single galaxies and galaxy pairs. Our clustering measurements and HOD model fits for the single galaxy samples are consistent with previous results. We find that the galaxy pairs generally have larger clustering amplitudes than single galaxies, and the quantities computed during the HOD fitting, e.g., effective halo mass, $M_{eff}$, and linear bias, $b_{g}$, are also larger for galaxy pairs. We find that the central fractions for galaxy pairs are significantly higher than single galaxies, which confirms that galaxy pairs are formed at the center of more massive dark matter haloes. We also model the clustering dependence of the galaxy pair correlation function on redshift, galaxy type, and luminosity. We find early-early pairs (bright galaxy pairs) cluster more strongly than late-late pairs (dim galaxy pairs), and that the clustering does not depend on the luminosity contrast between the two galaxies in the compact group.

[22]  arXiv:1407.8231 [pdf, ps, other]
Title: The role of massive halos in the Star Formation History of the Universe
Comments: 17 pages, 20 figures, submitted to A&A
Subjects: Astrophysics of Galaxies (astro-ph.GA)

The most striking feature of the Cosmic Star Formation History (CSFH) of the Universe is a dramatic drop of the star formation (SF) activity, since z~1. In this work we investigate if the very same process of assembly and growth of structures is one of the major drivers of the observed decline. We study the contribution to the CSFH of galaxies in halos of different masses. This is done by studying the total SFR-halo mass-redshift plane from redshift 0 to redshift z~1.6 in a sample of 57 groups and clusters by using the deepest available mid- and far-infrared surveys conducted with Spitzer MIPS and Herschel PACS and SPIRE. Our results show that low mass groups provide a 60-80% contribution to the CSFH at z~1. Such contribution declines faster than the CSFH in the last 8 billion years to less than 1% at z<0.3, where the overall SF activity is sustained by lower mass halos. More massive systems provide only a marginal contribution (<1%) at any epoch. A simplified abundance matching method shows that the large contribution of low mass groups at z~1 is due to a large fraction (>50%) of very massive, highly star forming Main Sequence galaxies. Below z~1 a quenching process must take place in massive halos to cause the observed faster suppression of their SF activity. Such process must be a slow one though, as most of the models implementing a rapid quenching of the SF activity in accreting satellites significantly underpredicts the observed SF level in massive halos at any redshift. Starvation or the transition from cold to hot accretion would provide a quenching timescale of 1 Gyrs more consistent with the observations. Our results suggest a scenario in which, due to the structure formation process, more and more galaxies experience the group environment and, thus, the associated quenching process. This leads to the progressive suppression of their SF activity shaping the CSFH below z~1.

[23]  arXiv:1407.8250 [pdf, ps, other]
Title: From Engine to Afterglow: Collapsars Naturally Produce Top-Heavy Jets and Early-Time Plateaus in Gamma Ray Burst Afterglows
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Fluid Dynamics (physics.flu-dyn)

We demonstrate that the steep decay and long plateau in the early phases of gamma ray burst (GRB) afterglows are naturally produced in the collapsar model, by a means ultimately related to the dynamics of relativistic jet propagation through a massive star. We present hydrodynamical simulations which start from a collapsar engine and evolve all the way through the late afterglow phase. The resultant outflow includes a jet core which is highly relativistic after breaking out of the star, but becomes baryon-loaded and less relativistic after colliding with a massive outer shell, corresponding to mass from the stellar atmosphere of the progenitor star which became trapped in front of the jet core at breakout. The prompt emission produced before or during this collision would then have the signature of a high Lorentz factor jet, but the afterglow is produced by the amalgamated post-collision ejecta which has more inertia than the original highly relativistic jet core and thus has a delayed deceleration. This naturally explains the early light curve behavior discovered by Swift, including a steep decay and a long plateau, without invoking late-time energy injection from the central engine. The numerical simulation is performed continuously from engine to afterglow, covering a dynamic range of over ten orders of magnitude in radius as a relativistic jet propagates through a massive star, breaks out of the stellar surface and coasts, generating both internal and external shocks. Light curves calculated from the numerical output demonstrate that this mechanism reproduces basic features seen in early afterglow data. Initial steep decays are produced by internal shocks, and the plateau corresponds to the coasting phase of the outflow.

[24]  arXiv:1407.8254 [pdf, ps, other]
Title: Gravitational waves from rapidly rotating neutron stars
Comments: To appear in 'Gravitational Waves Astrophysics: 3rd Session of the Sant Cugat Forum on Astrophysics, 2014', Editor: Carlos F. Sopuerta
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc)

Rapidly rotating neutron stars in Low Mass X-ray Binaries have been proposed as an interesting source of gravitational waves. In this chapter we present estimates of the gravitational wave emission for various scenarios, given the (electromagnetically) observed characteristics of these systems. First of all we focus on the r-mode instability and show that a 'minimal' neutron star model (which does not incorporate exotica in the core, dynamically important magnetic fields or superfluid degrees of freedom), is not consistent with observations. We then present estimates of both thermally induced and magnetically sustained mountains in the crust. In general magnetic mountains are likely to be detectable only if the buried magnetic field of the star is of the order of $B\approx 10^{12}$ G. In the thermal mountain case we find that gravitational wave emission from persistent systems may be detected by ground based interferometers. Finally we re-asses the idea that gravitational wave emission may be balancing the accretion torque in these systems, and show that in most cases the disc/magnetosphere interaction can account for the observed spin periods.

[25]  arXiv:1407.8260 [pdf, ps, other]
Title: Supernova remnant W49B and its environment
Authors: H. Zhu, W.W. Tian, P. Zuo
Comments: 11 pages, 13figures, accepted for publication in ApJ
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); High Energy Astrophysical Phenomena (astro-ph.HE)

We study Gamma-ray supernova remnant W49B and its environment using recent radio and infrared data. {\it Spitzer} IRS low resolution data of W49B shows shocked excitation lines of H$_{2}$ (0,0) S(0)-S(7) from the SNR-molecular cloud interaction. The H$_2$ gas is composed of two components with temperature of $\sim$260 K and $\sim$1060 K respectively. Various spectral lines from atomic and ionic particles are detected towards W49B. We suggest the ionic phase has an electron density of $\sim$500 cm${}^{-3}$ and a temperature of $\sim$${10^4}$ K by the spectral line diagnoses. The mid- and far-infrared data from {\it MSX}, {\it Spitzer} and {\it Herschel} reveals a 151 $\pm$ 20 K hot dust component with a mass of 7.5 $\pm$ 6.6 $\times$ ${10}^{-4} {\Msol}$ and a 45 $\pm$ 4 K warm dust component with a mass of 6.4 $\pm$ 3.2 ${\Msol}$. The hot dust is likely from materials swept up by the shock of W49B. The warm dust may possibly originate from the evaporation of clouds interacting with W49B. We build the HI absorption spectra of W49B and nearby four {\HII} regions (W49A, G42.90+0.58, G42.43-0.26 and G43.19-0.53), and study the relation between W49B and the surrounding molecular clouds by employing the 2.12 $\mu$m infrared and CO data. We therefore obtain a kinematic distance of $\sim$10 kpc for W49B and suggest that the remnant is likely associated with the CO cloud at about 40 km s$^{-1}$.

[26]  arXiv:1407.8262 [pdf, other]
Title: Primordial quantum nonequilibrium and large-scale cosmic anomalies
Comments: 37 pages
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); Quantum Physics (quant-ph)

We study incomplete relaxation to quantum equilibrium at long wavelengths, during a pre-inflationary phase, as a possible explanation for the reported large-scale anomalies in the cosmic microwave background (CMB). Our scenario makes use of the de Broglie-Bohm pilot-wave formulation of quantum theory, in which the Born probability rule has a dynamical origin. The large-scale power deficit could arise from incomplete relaxation for the amplitudes of the primordial perturbations. We show, by numerical simulations for a spectator scalar field, that if the pre-inflationary era is radiation dominated then the deficit in the emerging power spectrum will have a characteristic shape (an inverse-tangent dependence on wavenumber k, with oscillations). It is found that our scenario is able to produce a power deficit in the observed region and of the observed (approximate) magnitude for an appropriate choice of cosmological parameters. We also discuss the large-scale anisotropy, which could arise from incomplete relaxation for the phases of the primordial perturbations. We present numerical simulations for phase relaxation, and we show how to define characteristic scales for amplitude and phase nonequilibrium. The extent to which the data might support our scenario is left as a question for future work. Our results suggest that we have a potentially viable model that might explain two apparently independent cosmic anomalies by means of a single mechanism.

[27]  arXiv:1407.8264 [pdf, ps, other]
Title: A New Large Super-Fast Rotator: (335433) 2005 UW163
Comments: 18 pages, 4 figures, 1 table Accepted by ApJL
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Asteroids of size larger than 150 m generally do not have rotation periods smaller than 2.2 hours. This spin cutoff is believed to be due to the gravitationally bound rubble-pile structures of the asteroids. Rotation with periods exceeding this critical value will cause asteroid breakup. Up until now, only one object, 2001 OE84, has been found to be an exception to this spin cutoff. We report the discovery of a new super-fast rotator, (335433) 2005 UW163, spinning with a period of 1.290 hours and a lightcurve variation of $r'\sim0.8$ mag from the observations made at the P48 telescope and the P200 telescope of the Palomar Observatory. Its $H_{r'} = 17.69 \pm 0.27$ mag and multi-band colors (i.e., $g'-r' = 0.68\pm0.03$ mag, $r'-i' = 0.19\pm0.02$ mag and SDSS $i-z = -0.45$ mag) show it is a V-type asteroid with a diameter of $0.6 +0.3/-0.2$ km. This indicates (335433) 2005 UW163 is a super-fast rotator beyond the regime of the small monolithic asteroid.

[28]  arXiv:1407.8265 [pdf]
Title: Characterization of the Reflectivity of Various Black Materials
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Instrumentation and Detectors (physics.ins-det)

We present total and specular reflectance measurements of various materials that are commonly (and uncommonly) used to provide baffling and/or to minimize the effect of stray light in optical systems. More specifically, we investigate the advantage of using certain black surfaces and their role in suppressing stray light on detectors in optical systems. We measure the total reflectance of the samples over a broad wavelength range (250 < lambda < 2500 nm) that is of interest to astronomical instruments in the ultraviolet, visible, and near-infrared regimes. Additionally, we use a helium-neon laser to measure the specular reflectance of the samples at various angles. Finally, we compare these two measurements and derive the specular fraction for each sample.

[29]  arXiv:1407.8279 [pdf, ps, other]
Title: A new method of CCD dark current correction via extracting the dark information from scientific images
Comments: 8 pages, 5 figures, Proc. SPIE 9154 (2014)
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

We have developed a new method to correct dark current at relatively high temperatures for Charge-Coupled Device (CCD) images when dark frames cannot be obtained on the telescope. For images taken with the Antarctic Survey Telescopes (AST3) in 2012, due to the low cooling efficiency, the median CCD temperature was -46$^\circ$C, resulting in a high dark current level of about 3$e^-$/pix/sec, even comparable to the sky brightness (10$e^-$/pix/sec). If not corrected, the nonuniformity of the dark current could even overweight the photon noise of the sky background. However, dark frames could not be obtained during the observing season because the camera was operated in frame-transfer mode without a shutter, and the telescope was unattended in winter. Here we present an alternative, but simple and effective method to derive the dark current frame from the scientific images. Then we can scale this dark frame to the temperature at which the scientific images were taken, and apply the dark frame corrections to the scientific images. We have applied this method to the AST3 data, and demonstrated that it can reduce the noise to a level roughly as low as the photon noise of the sky brightness, solving the high noise problem and improving the photometric precision. This method will also be helpful for other projects that suffer from similar issues.

[30]  arXiv:1407.8280 [pdf, ps, other]
Title: The nonlinear photon transfer curve of CCDs and its effects on photometry
Comments: 10 pages, 7 figures, Proc. SPIE 9154 (2014)
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

The photon transfer curve (PTC, variance vs. signal level) is a commonly used and effective tool in characterizing CCD performance. It is theoretically linear in the range where photon shot noise dominates, and its slope is utilized to derive the gain of the CCD. However, recent researches on different CCDs have revealed that the variance progressively drops at high signal levels, while the linearity shown by signal versus exposure time is still excellent and unaffected. On the other hand, bright stars are found to exhibit fatter point spread function (PSF). Both nonlinear PTC and the brighter-fatter effect are regarded as the result of spreading of charges between pixels, an interaction progress increasing with signal level. In this work we investigate the nonlinear PTC based on the images with a STA1600FT CCD camera, whose PTC starts to become nonlinear at about 1/3 full well. To explain the phenomenon, we present a model to characterize the charge-sharing PSF. This signal-dependent PSF can be derived from flat-field frames, and allow us to quantify the effects on photometry and measured shape of stars. This effect is essentially critical for projects requiring accurate photometry and shape parameters.

[31]  arXiv:1407.8283 [pdf, ps, other]
Title: Problems with twilight/supersky flat-field for wide-field robotic telescopes and the solution
Comments: 7 pages, 5 figures, Proc. SPIE 9149 (2014)
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

Twilight/night sky images are often used for flat-fielding CCD images, but the brightness gradient in twilight/night sky causes problems of accurate flat-field correction in astronomical images for wide-field telescopes. Using data from the Antarctic Survey Telescope (AST3), we found that when the sky brightness gradient is minimum and stable, there is still a gradient of 1% across AST3's field-of-view of 4.3 square degrees. We tested various approaches to remove the varying gradients in individual flat-field images. Our final optimal method can reduce the spatially dependent errors caused by the gradient to the negligible level. We also suggest a guideline of flat-fielding using twilight/night sky images for wide-field robotic autonomous telescopes.

[32]  arXiv:1407.8298 [pdf, other]
Title: A Genetic Approach to the History of the Magellanic Clouds
Comments: 19 pages, 13 figures; Accepted for publication in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

The history of the Magellanic Clouds is investigated using N-body hydrodynamic simulations where the initial conditions are set by a genetic algorithm. This technique allows us to identify possible orbits for the Magellanic Clouds around the Milky Way, by directly comparing the simulations with observational constraints. We explore the parameter space of the interaction between the Magellanic Clouds and the Milky Way, considering as free parameters the proper motions of the Magellanic Clouds, the virial mass and the concentration parameter ($c$) of the Galactic dark matter halo. The best orbital scenarios presented here are considered with two different sets of parameters for the Milky Way disc and bulge components. The total circular velocity at the Sun's position ($\rm{R_{\odot}}=8.5\,\rm {kpc}$) is directly calculated from the rotation curve of the corresponding Galactic mass model. Our analysis suggests that the Magellanic Clouds have orbited inside the virial radius of the Milky Way for at least $3\,\rm{Gyr}$, even for low mass haloes. However, this is possible only with high values for the concentration parameter ($c\ge20$). In both orbital models presented here, the mutual interaction between the Magellanic Clouds is able to reproduce the observed features of the Magellanic System.

[33]  arXiv:1407.8306 [pdf, ps, other]
Title: The ESO UVES Advanced Data Products Quasar Sample - III. Evidence of Bimodality in the [N/alpha] Distribution
Authors: Tayyaba Zafar (1,2), Miriam Centurion (3), Celine Peroux (2), Paolo Molaro (3), Valentina D'Odorico (3), Giovanni Vladilo (3), Attila Popping (4) ((1) ESO, (2) LAM, (3) OAT, (4) ICRAR)
Comments: 16 pages, 14 figures, 12 tables, MNRAS accepted
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We report here a study of nitrogen and $\alpha$-capture element (O, S, and Si) abundances in 18 Damped Ly$\alpha$ Absorbers (DLAs) and sub-DLAs drawn from the ESO-UVES Advanced Data Products (EUADP) database. We report 9 new measurements, 5 upper and 4 lower limits of nitrogen that when compiled with available nitrogen measurements from the literature makes a sample of 108 systems. The extended sample presented here confirms the [N/$\alpha$] bimodal behaviour suggested in previous studies. Three-quarter of the systems show $\langle$[N/$\alpha$]$\rangle=-0.85$ ($\pm$0.20 dex) and one-quarter ratios are clustered at $\langle$[N/$\alpha$]$\rangle= -1.41$ ($\pm$0.14 dex). The high [N/$\alpha$] plateau is consistent with the HII regions of dwarf irregular and blue compact dwarf galaxies although extended to lower metallicities and could be interpreted as the result of a primary nitrogen production by intermediate mass stars. The low [N/$\alpha$] values are the lowest ever observed in any astrophysical site. In spite of this fact, even lower values could be measured with the present instrumentation, but we do not find them below [N/$\alpha$] $\approx$ $-1.7$. This suggests the presence of a floor in [N/$\alpha$] abundances, which along with the lockstep increase of N and Si may indicate a primary nitrogen production from fast rotating, massive stars in relatively young or unevolved systems.

[34]  arXiv:1407.8307 [pdf, ps, other]
Title: Optical and infrared emission of H II complexes as a clue to PAHs lifecycle
Comments: Accepted to MNRAS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

We present an analysis of optical spectroscopy and infrared aperture photometry of more than 100 H II complexes in nine galaxies. Spectra obtained with the 6-m telescope of SAO RAS are used along with archival data from Spitzer and several ground-based telescopes to infer a strength of polycyclic aromatic hydrocarbon (PAH) emission, age, properties of the UV radiation field, and metallicity of studied H II complexes. Physical properties (age, radiation field parameters, metallicity) are related to the $F_{8}/F_{24}$ ratio used as a proxy for the PAH abundance in order to reveal factors that may influence the PAH evolution in H II complexes. The well-known correlation between the $F_{8}/F_{24}$ ratio and metallicity is confirmed in the studied complexes. The infrared flux ratio also correlates with the [O III]$\lambda 5007/\mathrm{H\beta}$ ratio which is often considered as an indicator of the radiation field hardness, but this correlation seems to be a mere reflection of a correlation between [O III]$\lambda 5007/\mathrm{H\beta}$ and metallicity. In separate metallicity bins, the $F_{8}/F_{24}$ ratio is found to correlate with an age of an H II complex, which is estimated from the equivalent width of $\mathrm{H}\beta$ line. The correlation is positive for low metallicity complexes and negative for high metallicity complexes. Analysing various mechanisms of PAH formation and destruction in the context of found correlations, we suggest that PAH abundance is likely altered by the UV radiation within H II complexes, but this is not necessarily due to their destruction. If PAHs can also form in H II complexes due to some processes like aromatisation, photodestruction, shattering and sputtering of very small grains, the net $F_{8}/F_{24}$ ratio is determined by a balance between all these processes that can be different at different metallicities.

[35]  arXiv:1407.8317 [pdf, other]
Title: Star catalog position and proper motion corrections in asteroid astrometry
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)

We provide a scheme to correct asteroid astrometric observations for star catalog systematic errors due to inaccurate star positions and proper motions. As reference we select the most accurate stars in the PPMXL catalog, i.e., those based on 2MASS astrometry. We compute position and proper motion corrections for 19 of the most used star catalogs. The use of these corrections provides better ephemeris predictions and improves the error statistics of astrometric observations, e.g., by removing most of the regional systematic errors previously seen in Pan-STARRS PS1 asteroid astrometry. The correction table is publicly available at this ftp URL and can be freely used in orbit determination algorithms to obtain more reliable asteroid trajectories.

[36]  arXiv:1407.8333 [pdf, ps, other]
Title: Method for all-sky searches of continuous gravitational wave signals using the frequency-Hough transform
Comments: 27 pages, 20 figures, PRD in press
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

In this paper we present a hierarchical data analysis pipeline for all-sky searches of continuous gravitational wave signals, like those emitted by spinning neutron stars asymmetric with respect to the rotation axis, with unknown position, rotational frequency and spin-down. The core of the pipeline is an incoherent step based on a particularly efficient implementation of the Hough transform, that we call frequency-Hough, that maps the data time-frequency plane to the source frequency/spin-down plane for each fixed direction in the sky. Theoretical ROCs and sensitivity curves are computed and the dependency on various thresholds is discussed. A comparison of the sensitivity loss with respect to an "optimal" method is also presented. Several other novelties, with respect to other wide-parameter analysis pipelines, are also outlined. They concern, in particular, the construction of the grid in the parameter space, with over-resolution in frequency and parameter refinement, candidate selection and various data cleaning steps which are introduced to improve search sensitivity and rejection of false candidates.

[37]  arXiv:1407.8338 [pdf, other]
Title: Neutrino constraints: what large-scale structure and CMB data are telling us?
Comments: 24 pages, 8 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

(Abridged) We discuss the reliability of neutrino mass constraints, either active or sterile, from the combination of WMAP 9-year or Planck CMB data with BAO measurements from BOSS DR11, galaxy shear measurements from CFHTLenS, SDSS Ly-$\alpha$ forest constraints and galaxy cluster mass function from Chandra observations. To avoid model dependence of the constraints we perform a full likelihood analysis for all the datasets employed. As for the cluster data analysis we rely on to the most recent calibration of massive neutrino effects in the halo mass function and we explore the impact of the uncertainty in the mass bias and re-calibration of the halo mass function due to baryonic feedback processes on cosmological parameters. We find that none of the low redshift probes alone provide evidence for massive neutrinos in combination with CMB measurements, while a larger than $2\sigma$ detection of non zero neutrino mass, either active or sterile, is achieved combining cluster or shear data with CMB and BAO measurements. The preference for massive neutrino is larger in the sterile neutrino scenario, and for the combination of Planck, BAO, shear and cluster datasets we find that the vanilla $\Lambda$CDM model is rejected at more than $3\sigma$ and a sterile neutrino mass as motivated by accelerator anomaly is within the $2\sigma$ errors. Finally, results from the full data combination reflect the tension between the $\sigma_8$ constraints obtained from cluster and shear data and that inferred from Ly-$\alpha$ forest measurements; in the active neutrino scenario for both CMB datasets employed, the full data combination yields only an upper limits on $\sum m_\nu$, while assuming an extra sterile neutrino we still get preference for non-vanishing mass, $m_s^{\rm eff}=0.26^{+0.22}_{-0.24}$ eV, and dark contribution to the radiation content, $\Delta N_{\rm eff}=0.82\pm0.55$.

[38]  arXiv:1407.8347 [pdf, other]
Title: Molecular tendrils feeding star formation in the Eye of the Medusa - The Medusa merger in high resolution 12CO 2-1 maps
Comments: accepted for publication in A&A, 12 pages, 9 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Studying molecular gas properties in merging galaxies gives us important clues to the onset and evolution of interaction-triggered starbursts. NGC4194 is particularly interesting to study since its FIR-to-CO luminosity ratio rivals that of ULIRGs,despite its lower luminosity compared to ULIRGs, which indicates a high star formation efficiency that is relative to even most spirals and ULIRGs.We study the molecular medium at an angular resolution of 0.65"x .52" through our observations of CO2-1 emission using the SMA. We compare our CO2-1 maps with optical HST and high angular resolution radio continuum images to study the relationship between molecular gas and other components of the starburst region. The molecular gas is tracing the complicated dust lane structure of NGC4194 with the brightest emission being located in an off-nuclear ring-like structure with ~320pc radius, the Eye of the Medusa. The bulk CO emission of the ring is found south of the kinematical center of NGC4194. The northern tip of the ring is associated with the galaxy nucleus, where the radio continuum has its peak. A prominent, secondary emission maximum in the radio continuum is located inside the molecular ring. This suggests that the morphology of the ring is partially influenced by massive supernova explosions. From the combined evidence, we propose that the Eye of the Medusa contains a shell of swept up material where we identify a number of giant molecular associations. We propose that the Eye may be the site of an efficient starburst of 5-7M_sun/yr, but it would still constitute only a fraction of the 30-50M_sun/yr SFR of NGC4194. Furthermore, we find that ~50% of the molecular mass of NGC4194 is found in extended filamentary-like structures tracing the minor and major axis dust lanes. We suggest that molecular gas is transported along these lanes providing the central starburst region with fuel.

[39]  arXiv:1407.8366 [pdf, ps, other]
Title: What Regulates Galaxy Evolution? Open Questions in Our Understanding of Galaxy Formation and Evolution
Authors: Gabriella De Lucia (INAF), Adam Muzzin (Leiden), Simone Weinmann (Leiden)
Comments: 36 pages, 6 Figures, submitted to New Astronomy Reviews
Subjects: Astrophysics of Galaxies (astro-ph.GA)

In April 2013, a workshop entitled "What Regulates Galaxy Evolution" was held at the Lorentz Center. The aim of the workshop was to bring together the observational and theoretical community working on galaxy evolution, and to discuss in depth of the current problems in the subject, as well as to review the most recent observational constraints. A total of 42 astrophysicists attended the workshop. A significant fraction of the time was devoted to identifying the most interesting "open questions" in the field, and to discuss how progress can be made. This review discusses the four questions (one for each day of the workshop) that, in our opinion, were the focus of the most intense debate. We present each question in its context, and close with a discussion of what future directions should be pursued in order to make progress on these problems.

[40]  arXiv:1407.8370 [pdf, ps, other]
Title: A study of dynamical processes in the Orion KL region using ALMA-- Probing molecular outflow and inflow
Comments: Accepted to ApJ
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

This work reports a high spatial resolution observations toward Orion KL region with high critical density lines of CH$_{3}$CN (12$_{4}$-11$_{4}$) and CH$_{3}$OH (8$_{-1, 8}$-7$_{0, 7}$) as well as continuum at $\sim$1.3 mm band. The observations were made using the Atacama Large Millimeter/Submillimeter Array with a spatial resolution of $\sim$1.5$^{\prime\prime}$ and sensitives about 0.07 K and $\sim$0.18 K for continuum and line, respectively. The observational results showed that the gas in the Orion KL region consists of jet-propelled cores at the ridge and dense cores at east and south of the region, shaped like a wedge ring. The outflow has multiple lobes, which may originate from an explosive ejection and is not driven by young stellar objects. Four infrared bubbles were found in the Spitzer/IRAC emissions. These bubbles, the distributions of the previously found H$_2$ jets, the young stellar objects and molecular gas suggested that BN is the explosive center. The burst time was estimated to be $\leq$ 1300 years. In the mean time, signatures of gravitational collapse toward Source I and hot core were detected with material infall velocities of 1.5 km~s$^{-1}$ and $\sim$ 0.6 km~s$^{-1}$, corresponding to mass accretion rates of 1.2$\times$10$^{-3}$M$_{\sun}$/Yr and 8.0$\times$10$^{-5}$M$_{\sun}$/Yr, respectively. These observations may support that high-mass stars form via accretion model, like their low-mass counterparts.

[41]  arXiv:1407.8396 [pdf, ps, other]
Title: Effects of stellar evolution and ionizing radiation on the environments of massive stars
Comments: 5 pages, 2 figures, conference proceedings in "Wind Bubbles, Astrospheres and the Heliosphere: Environments and Cosmic Rays", Bochum, Germany (Nov 2013). Published in ASTRA proceedings, an Open Access Journal for Refereed Proceedings in Extraterrestrial Research
Subjects: Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)

We discuss two important effects for the astrospheres of runaway stars: the propagation of ionizing photons far beyond the astropause, and the rapid evolution of massive stars (and their winds) near the end of their lives. Hot stars emit ionizing photons with associated photoheating that has a significant dynamical effect on their surroundings. 3D simulations show that HII regions around runaway O stars drive expanding conical shells and leave underdense wakes in the medium they pass through. For late O stars this feedback to the interstellar medium is more important than that from stellar winds. Late in life, O stars evolve to cool red supergiants more rapidly than their environment can react, producing transient circumstellar structures such as double bow shocks. This provides an explanation for the bow shock and linear bar-shaped structure observed around Betelgeuse.

[42]  arXiv:1407.8397 [pdf, ps, other]
Title: Simulating AIA observations of a flux rope ejection
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Extreme ultraviolet (EUV) images from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory (SDO) are providing new insights into the early phase of CME evolution. Observations now show the ejection of magnetic flux ropes from the solar corona and how they evolve into CMEs. These observations are difficult to interpret in terms of basic physical mechanisms and quantities. To fully understand CMEs we need to compare equivalent quantities derived from both observations and theoretical models. To this end we aim to produce synthesised AIA observations from simluations of a flux rope ejection. To carry this out we include the role of thermal conduction and radiative losses, both of which are important for determining the temperature distribution of the solar corona during a CME. We perform a simulation where a flux rope is ejected from the solar corona. From the density and temperature of the plasma in the simulation we synthesise AIA observations. The emission is then integrated along the line of sight using the instrumental response function of AIA. We sythesise observations of AIA in the channels at 304 A, 171 A, 335 A, and 94 A. The synthesised observations show a number of features similar to actual observations and in particular reproduce the general development of CMEs in the low corona as observed by AIA. In particular we reproduce an erupting and expanding arcade in the 304 A and 171 A channels with a high density core. The ejection of a flux rope reproduces many of the features found in the AIA observations. This work is therefore a step forward in bridging the gap between observations and models, and can lead to more direct interpretations of EUV observations in terms of flux rope ejections. We plan to improve the model in future studies in order to perform a more quantitative comparison.

[43]  arXiv:1407.8414 [pdf, ps, other]
Title: Nonlinear growing neutrino cosmology
Comments: 13 pages, 9 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

The energy scale of Dark Energy, $\sim 2 \times 10^{-3}$ eV, is a long way off compared to all known fundamental scales - except for the neutrino masses. If Dark Energy is dynamical and couples to neutrinos, this is no longer a coincidence. The time at which Dark Energy starts to behave as an effective cosmological constant can be linked to the time at which the cosmic neutrinos become nonrelativistic. This naturally places the onset of the Universe's accelerated expansion in recent cosmic history, addressing the why-now problem of Dark Energy. We show that these mechanisms indeed work in the Growing Neutrino Quintessence model - even if the fully nonlinear structure formation and backreaction are taken into account, which were previously suspected of spoiling the cosmological evolution. The attractive force between neutrinos arising from their coupling to Dark Energy grows as large as $10^6$ times the gravitational strength. This induces very rapid dynamics of neutrino fluctuations which are nonlinear at redshift $z \approx 2$. Nevertheless, a nonlinear stabilization phenomenon ensures only mildly nonlinear oscillating neutrino overdensities with a large-scale gravitational potential substantially smaller than that of cold dark matter perturbations. Depending on model parameters, the signals of large-scale neutrino lumps may render the cosmic neutrino background observable.

[44]  arXiv:1407.8425 [pdf, ps, other]
Title: Stellar physical parameters from Str ömgren photometry. Application to the young stars in the Galactic anticenter survey
Comments: 13 pages, 15 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Aims. The aim is to derive accurate stellar distances and extinctions for young stars of our survey in the Galactic anticenter direction using the Str\"omgren photometric system. This will allow a detailed mapping of the stellar density and absorption toward the Perseus arm. Methods. We developed a new method for deriving physical parameters from Str\"omgren photometry and also implemented and tested it. This is a model-based method that uses the most recent available stellar atmospheric models and evolutionary tracks to interpolate in a 3D grid of the unreddened indexes [m1], [c1] and Hbeta. Distances derived from both this method and the classical pre-Hipparcos calibrations were tested against Hipparcos parallaxes and found to be accurate. Results. Systematic trends in stellar photometric distances derived from empirical calibrations were detected and quantified. Furthermore, a shift in the atmospheric grids in the range Teff=[7000,9000]K was detected and a correction is proposed. The two methods were used to compute distances and reddening for about 12000 OBA-type stars in our Str\"omgren anticenter survey. Data from the IPHAS and 2MASS catalogs were used to complement the detection of emission line stars and to break the degeneracy between early and late photometric regions. We note that photometric distances can differ by more than 20%, those derived from the empirical calibrations being smaller than those derived with the new method, which agree better with the Hipparcos data.

[45]  arXiv:1407.8429 [pdf, other]
Title: APEX observations of supernova remnants - I. Non-stationary MHD-shocks in W44
Comments: 20 pages, 13 figures, 13 tables, accepted for publication in Astronomy and Astrophysics
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Aims. The interaction of supernova remnants (SNRs) with molecular clouds gives rise to strong molecular emission in the far-IR and sub-mm wavelength regimes. The application of MHD shock models in the interpretation of this line emission can yield valuable information on the energetic and chemical impact of supernova remnants. Methods. New mapping observations with the APEX telescope in CO (3-2), (4-3), (6-5), (7-6) and 13CO (3-2) towards two regions in the supernova remnant W44 are presented. Integrated intensities are extracted on five different positions, corresponding to local maxima of CO emission. The integrated intensities are compared to the outputs of a grid of models, which combine an MHD shock code with a radiative transfer module based on the large velocity gradient approximation. Results. All extracted spectra show ambient and line-of-sight components as well as blue- and red-shifted wings indicating the presence of shocked gas. Basing the shock model fits only on the highest-lying transitions that unambiguously trace the shock-heated gas, we find that the observed CO line emission is compatible with non-stationary shocks and a pre-shock density of 10^4 cm-3. The ages of the modelled shocks scatter between values of \sim1000 and \sim3000 years. The shock velocities in W44F are found to lie between 20 and 25 km/s, while in W44E fast shocks (30-35 km/s) as well as slower shocks (\sim20 km/s) are compatible with the observed spectral line energy diagrams. The pre-shock magnetic field strength components perpendicular to the line of sight in both regions have values between 100 and 200 \muG. Our best-fitting models allow us to predict the full ladder of CO transitions, the shocked gas mass in one beam as well as the momentum- and energy injection.

[46]  arXiv:1407.8434 [pdf, ps, other]
Title: A stellar population synthesis approach to the Oosterhoff dichotomy
Comments: 12 pages, 7 figures, accepted for publication by MNRAS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We use color-magnitude diagram synthesis together with theoretical relations from non-linear pulsation models to approach the long-standing problem of the Oosterhoff dichotomy related to the distribution of the mean periods of fundamental RR Lyrae variables in globular clusters. By adopting the chemical composition determined from spectroscopic observations and a criterion to account for the hysteresis mechanism, we tuned age and mass-loss to simultaneously reproduce the morphology of both the turn-off and the Horizontal Branch of a sample of 17 globular clusters of the Milky Way and of nearby dwarf galaxies in the crucial metallicity range (-1.9<[Fe/H]<-1.4) where the Oostheroff transition is apparent. We find that the Oosterhoff dichotomy among Galactic globular clusters is naturally reproduced by models. The analysis of the relative impact of the various involved parameters indicates that the main responsibles of the dichotomy are the peculiar distribution of clusters in the age-metallicity plane and the hysteresis. In particular, there is a clear connection between the two main branches of the age-metallicity relation for Galactic globular clusters and the Oosterhoff groups. The properties of clusters' RR Lyrae belonging to other Oostheroff groups (OoInt and OoIII) are instead not well reproduced. While for OoIII clusters a larger helium abundance for a fraction of the cluster's stars can reconcile the model prediction with observations, some other parameter affecting both the Horizontal Branch morphology and the RR Lyrae periods is required to reproduce the behavior of OoInt clusters.

[47]  arXiv:1407.8439 [pdf, ps, other]
Title: Resilience of the standard predictions for primordial tensor modes
Comments: 5 pages
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)

We show that the prediction for the primordial tensor power spectrum cannot be modified at leading order in derivatives. Indeed, one can always set to unity the speed of propagation of gravitational waves during inflation by a suitable disformal transformation of the metric, while a conformal one can make the Planck mass time-independent. Therefore, the tensor-to-scalar ratio unambiguously fixes the energy scale of inflation. Using the Effective Field Theory of Inflation, we check that predictions are independent of the choice of frame, as expected. The first corrections to the standard prediction come from two parity violating operators with three derivatives. Also the correlator $\langle\gamma\gamma\gamma\rangle$ is standard and only receives higher derivative corrections. These results hold also in multifield models of inflation and in alternatives to inflation and make the connection between a (quasi) scale-invariant tensor spectrum and inflation completely robust.

[48]  arXiv:1407.8445 [pdf, other]
Title: Theoretical deduction of the Hubble law beginning with a MoND theory in context of the $Λ$FRW-Cosmology
Authors: N. Falcon, A. Aguirre
Comments: 13 pages, 2 figures, under review in AJ
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We deducted the Hubble law and the age of the Universe, through the introduction of the Inverse Yukawa Field (IYF), as a non-local additive complement of the Newtonian gravitation (Modified Newtonian Dynamics). As result we connected the dynamics of astronomical objects at great scale with the Friedmann-Robertson-Walker ($\Lambda$FRW) model. From the corresponding formalism, the Hubble law can be expressed as v = (4 $\pi$ [G]/c)r, which was derivated by evaluating the IYF force at distances much greater than 50Mpc, giving a maximum value for the expansion rate of the universe of $H_0=86,31$, consistent with the observational data of 392 astronomical objects from NASA/IPAC Extragalactic Database (NED). This additional field (IYF) provides a simple interpretation of dark energy as the action a large scale of baryonic matter. Additionally, we calculated the age of the universe as 11Gyr, in agreement with recent measurements of the age of the white dwarfs in the solar neighborhood.

[49]  arXiv:1407.8446 [pdf, ps, other]
Title: A comparison of reconstruction methods for the estimation of CME kinematics based on SECCHI/HI observations
Comments: 40pages, 10 figures, Published in ApJ
Journal-ref: 2014, ApJ, 784, 135
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Space Physics (physics.space-ph)

A study of the kinematics and arrival times of CMEs at Earth, derived from time-elongation maps (J-maps) constructed from STEREO/Heliospheric Imager (HI) observations, provides an opportunity to understand the heliospheric evolution of CMEs in general. We implement various reconstruction techniques, based on the use of time-elongation profiles of propagating CMEs viewed from single or multiple vantage points, to estimate the dynamics of three geo-effective CMEs. We use the kinematic properties, derived from analysis of the elongation profiles, as inputs to the Drag Based Model for the distance beyond which the CMEs cannot be tracked unambiguously in the J-maps. The ambient solar wind into which these CMEs, which travel with different speeds, are launched, is different. Therefore, these CMEs will evolve differently throughout their journey from the Sun to 1 AU. We associate the CMEs, identified and tracked in the J-maps, with signatures observed in situ near 1 AU by the WIND spacecraft. By deriving the kinematic properties of each CME, using a variety of existing methods, we assess the relative performance of each method for the purpose of space weather forecasting. We discuss the limitations of each method, and identify the major constraints in predicting the arrival time of CMEs near 1 AU using heliospheric imager observations.

[50]  arXiv:1407.8452 [pdf, other]
Title: The Mass-Loss Return from Evolved Stars to the Large Magellanic Cloud IV: Construction and Validation of a Grid of Models for Oxygen-Rich AGB Stars, Red Supergiants, and Extreme AGB Stars
Comments: 49 pages, 15 figures, appeared in the 20 February 2011 issue of Astrophysical Journal
Journal-ref: Ap.J. 728 (2011) 93
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

To measure the mass loss from dusty oxygen-rich (O-rich) evolved stars in the Large Magellanic Cloud (LMC), we have constructed a grid of models of spherically-symmetric dust shells around stars with constant mass-loss rates using 2Dust. These models will constitute the O-rich model part of the "Grid of Red supergiant and Asymptotic giant branch star ModelS" (GRAMS). This model grid explores 4 parameters - stellar effective temperature from 2100 K - 4700 K; luminosity from 10^3-10^6 L_Sun; dust shell inner radii of 3, 7, 11, and 15 R_Star; and 10.0 micron optical depth from 10^-4 to 26. From an initial grid of ~1200 2Dust models, we create a larger grid of ~69,000 models by scaling to cover the luminosity range required by the data. These models are offered to the public on a website. The matching in color-magnitude diagrams and color-color diagrams to observed O-rich asymptotic giant branch (AGB) and red supergiant (RSG) candidate stars from the SAGE and SAGE-Spec LMC samples and a small sample of OH/IR stars is generally very good. The extreme AGB star candidates from SAGE are more consistent with carbon-rich (C-rich) than O-rich dust composition. Our model grid suggests lower limits to the mid-infrared colors of the dustiest AGB stars for which the chemistry could be O-rich. Finally, the fitting of GRAMS models to SEDs of sources fit by other studies provides additional verification of our grid and anticipates future, more expansive efforts.

[51]  arXiv:1407.8453 [pdf, ps, other]
Title: CO J = 2 - 1 Emission from Evolved Stars in the Galactic Bulge
Comments: 40 pages, 16 figures, appeared in the 1 March 2013 issue of the Astrophysical Journal
Journal-ref: Ap. J. 765 (2013) 20
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We observe a sample of 8 evolved stars in the Galactic Bulge in the CO J = 2 - 1 line using the Submillimeter Array (SMA) with angular resolution of 1 - 4 arcseconds. These stars have been detected previously at infrared wavelengths, and several of them have OH maser emission. We detect CO J = 2 - 1 emission from three of the sources in the sample: OH 359.943 +0.260, [SLO2003] A12, and [SLO2003] A51. We do not detect the remaining 5 stars in the sample because of heavy contamination from the galactic foreground CO emission. Combining CO data with observations at infrared wavelengths constraining dust mass loss from these stars, we determine the gas-to-dust ratios of the Galactic Bulge stars for which CO emission is detected. For OH 359.943 +0.260, we determine a gas mass-loss rate of 7.9 (+/- 2.2) x 10^-5 M_Sun/year and a gas-to-dust ratio of 310 (+/- 89). For [SLO2003] A12, we find a gas mass-loss rate of 5.4 (+/- 2.8) x 10^-5 M_Sun/year and a gas-to-dust ratio of 220 (+/- 110). For [SLO2003] A51, we find a gas mass-loss rate of 3.4 (+/- 3.0) x 10^-5 M_Sun/year and a gas-to-dust ratio of 160 (+/- 140), reflecting the low quality of our tentative detection of the CO J = 2 - 1 emission from A51. We find the CO J = 2 - 1 detections of OH/IR stars in the Galactic Bulge require lower average CO J = 2 - 1 backgrounds.

[52]  arXiv:1407.8456 [pdf, ps, other]
Title: Effect of cross-redistribution on the resonance scattering polarization of O {\sc i} line at 1302 Å\,
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Oxygen is the most abundant element on the Sun after Hydrogen and Helium. The intensity spectrum of resonance lines of neutral Oxygen namely O {\sc i} (1302, 1305 and 1306 \AA\,) has been studied in the literature for chromospheric diagnostics. In this paper we study the resonance scattering polarization in the O {\sc i} line at 1302 \AA\, using two-dimensional radiative transfer in a composite atmosphere constructed using a two-dimensional magneto-hydrodynamical snapshot in the photosphere and columns of the one-dimensional FALC atmosphere in the chromosphere. The methods developed by us recently in a series of papers to solve multi-dimensional polarized radiative transfer have been incorporated in our new code POLY2D which we use for our analysis. We find that multi-dimensional radiative transfer including XRD effects is important in reproducing the amplitude and shape of scattering polarization signals of the O {\sc i} line at 1302 \AA\,.

[53]  arXiv:1407.8462 [pdf, ps, other]
Title: Recent highlights from ARGO-YBJ
Authors: Di Sciascio Giuseppe on behalf of the ARGO-YBJ Collaboration (INFN - Sezione Roma Tor Vergata, Roma, Italy)
Comments: Talk given at TAUP 2013 Conference 8-13 September 2013, Asilomar, CA, USA
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Experiment (hep-ex)

The ARGO-YBJ experiment has been in stable data taking for 5 years at the YangBaJing Cosmic Ray Observatory (Tibet, P.R. China, 4300 m a.s.l., 606 g/cm^2). With a duty-cycle greater than 86% the detector collected about 5 X 10^{11} events in a wide energy range, from few hundreds GeV up to the PeV. A number of open problems in cosmic ray physics has been faced exploiting different analyses. In this paper we summarize the latest results in gamma-ray astronomy and in cosmic ray physics

[54]  arXiv:1407.8482 [pdf, ps, other]
Title: Improving robustness of exoplanetary orbital fits through a regularization of the white and red Doppler noise models. Hints of a 13-year star-spot activity cycle of 55 Cancri
Authors: Roman V. Baluev
Comments: 21 pages, 12 figures, 3 tables; Revised version submitted to MNRAS
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Solar and Stellar Astrophysics (astro-ph.SR)

We consider the impact of the Doppler noise model on the statistical robustness of the exoplanetary radial-velocity fits. We show that the traditional model of the Doppler noise with an additive jitter can generate large non-linearity effects, decreasing the reliability of the fit, especially in the cases when a correleated Doppler noise is involved. We introduce a regularization of the additive noise model that can gracefully eliminate its singularities together with the associated non-linearity effects.
We apply this approach to Doppler time-series data of several exoplanetary systems. It demonstrates that our new regularized noise model yields orbital fits that have either increased or at least the same statistical robustness, in comparison with the simple additive jitter. Various statistical uncertainties in the parametric estimations are often reduced, while planet detection significance is often increased.
Concerning the 55 Cnc five-planet system, we show that its Doppler data contain significant correlated ("red") noise. Its correlation timescale is in the range from days to months, and its magnitude is much larger than the effect of the planetary N-body perturbations in the radial velocity (these perturbations thus appear undetectable). Characteristics of the red noise depend on the spectrograph/observatory, and also show a cyclic time variation in phase with the public Ca II H&K and photometry measurements. We interpret this modulation as a hint of the long-term activity cycle of 55 Cnc, similar to the Solar 11-year cycle. We estimate the 55 Cnc activity period by 12.6 (+2.5,-1.0) yrs, with the nearest minimum presumably expected in 2014 or 2015.

[55]  arXiv:1407.8489 [pdf, other]
Title: Life Cycle of Dust in the Magellanic Clouds and the Milky Way
Comments: 18 pages, 6 figures, published recently online in the Proceedings of Science for the conference: Life Cycle of Dust in the Universe, Observations, Theory and Laboratory Experiments
Journal-ref: PoS(LCDU2013)016
Subjects: Astrophysics of Galaxies (astro-ph.GA)

To a great extent, our understanding of the life cycle of dust is based on the observational and theoretical studies of the Milky Way and the Magellanic Clouds, which will be the topic of this contribution. Over past years, a large volume of observations with unprecedented spatial resolution has been accumulated for the Milky Way. It permits investigations of different stages of the life cycle of dust, from its formation in stellar sources to destruction in star-forming regions and supernovae shocks. Observations of dust emission, extinction, polarisation of light, and interstellar element depletions in the solar neighbourhood provide the most accurate constraints for the reference dust models applied to study extragalactic systems. However, global spatial studies of the circumstellar and interstellar dust are complicated in the Milky Way disk because of high extinction, confusion along the line of sight and large uncertainties in distances. In contrast, the favourable location in the sky and the proximity of the Magellanic Clouds allow detailed multi-wavelength studies of the dust-forming stellar populations and the investigation of variations of the interstellar grain properties for the entire galaxies. They enable the first comparison between the global stardust production rates from theoretical calculations and those from observations, which confirm discrepancy between accumulated stardust mass and observed interstellar dust mass - "the missing dust-source" problem. Modelling of the life cycle of dust in the Large Magellanic Cloud showed that dust growth by mantle accretion in the ISM, a major dust source in the Milky Way, can be responsible for the existing dust mass in the LMC. We will present comparison of the dust input from different sources to the dust budgets of the Milky Way and the Magellanic Clouds, which reveals how the role of these dust sources depends on metallicity.

[56]  arXiv:1407.8500 [pdf, ps, other]
Title: Explaining the Observed Relation Between Stellar Activity and Rossby Number
Authors: Eric G. Blackman (U. Rochester), John H. Thomas (U. Rochester)
Comments: 5 pages, 1 figure, submitted to MNRAS Letters
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Observations of late-type main-sequence stars have revealed an empirical scaling of coronal activity versus Rossby number Ro (a ratio of rotation period to convective turnover time) which has hitherto lacked a theoretical explanation. For Ro >> 1, the activity measured as X-ray to bolometric flux varies as Ro^{-q} with q between 2 and 3, whilst q=0 for Ro << 1. Here we provide physical arguments to explain the transition between these two regimes and the power law in the Ro >> 1 regime. We do so by constructing an expression for the coronal luminosity based on dynamo magnetic field generation and magnetic buoyancy. We explain the Ro<<1 behavior from the inference that observed rotation is a proxy for differential rotation and argue that once the shear time scale is shorter than the convective turnover time, eddies will be shredded on the shear time scale and so the eddy correlation time actually becomes the shear time and the convection time drops out of the equations, explaining the q~0 regime. We explain the finite q of the Ro >> 1 regime using a dynamo saturation theory based on magnetic helicity buildup and buoyant loss.

[57]  arXiv:1407.8502 [pdf, other]
Title: Power spectrum tomography of dark matter annihilation with local galaxy distribution
Authors: Shin'ichiro Ando
Comments: 28 pages, 14 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE)

Cross-correlating the gamma-ray background with local galaxy catalogs potentially gives stringent constraints on dark matter annihilation. We provide updated theoretical estimates of sensitivities to the annihilation cross section from gamma-ray data with Fermi telescope and 2MASS galaxy catalogs, by elaborating the galaxy power spectrum and astrophysical backgrounds, and adopting the Markov-Chain Monte Carlo simulations. In particular, we show that taking tomographic approach by dividing the galaxy catalogs into more than one redshift slice will improve the sensitivity by a factor of a few to several. If dark matter halos contain lots of bright substructures, yielding a large annihilation boost, then one may be able to probe the canonical annihilation cross section for thermal production mechanism up to masses of $\sim$700 GeV. Even with modest substructure boost, on the other hand, the sensitivities could still reach a factor of three larger than the canonical cross section for dark matter masses of tens to a few hundreds of GeV.

[58]  arXiv:1407.8503 [pdf, other]
Title: Plasma Leakage from the Centrifugal Magnetospheres of Magnetic B-Type Stars
Comments: 2 pages, 1 figure, proceedings of the IAU Symposium 307 held in Geneva in June 2014
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Magnetic B-type stars are often host to Centrifugal Magnetospheres (CMs). Here we describe the results of a population study encompassing the full sample of known magnetic early B-type stars, focusing on those with detectable CMs. We present revised rotational and magnetic parameters for some stars, clarifying their positions on the rotation-confi?nement diagram, and? find that plasma densities within their CMs are much lower than those predicted by centrifugal breakout.

[59]  arXiv:1407.8505 [pdf, other]
Title: $ξ^1$ CMa: An Extremely Slowly Rotating Magnetic B0.7 IV Star
Comments: 2 pages, 1 figure, proceedings of the IAU Symposium 307 held in Geneva in June 2014
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We present our analysis of 6 years of ESPaDOnS spectropolarimetry of the magnetic $\beta$ Cep star $\xi^1$ CMa (B0.7 IV). This high-precision magnetometry is consistent with a rotational period $P{\rm rot} >$ 40 yr. Absorption line profiles can be reproduced with a non-rotating model. We constrain $R_*$, $L_*$, and the stellar age via a Baade-Wesselink analysis. Spindown due to angular momentum loss via the magnetosphere predicts an extremely long rotational period if the magnetic dipole $B_{\rm d} > 6$ kG, a strength also inferred by the best-fit sinusoids to the longitudinal magnetic field measurements $B_{\rm Z}$ when phased with a 60-year $P_{\rm rot}$.

[60]  arXiv:1407.8525 [pdf, ps, other]
Title: Constraining the neutrino emission of gravitationally lensed Flat-Spectrum Radio Quasars with ANTARES data
Comments: 5 pages, 1 figure
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Context. The jets of radio-loud Active Galactic Nuclei are among the most powerful particle accelerators in the Universe, and a plausible production site for high-energy cosmic rays. The detection of high-energy neutrinos from these sources would provide unambiguous evidence of a hadronic component in such jets. High-luminosity blazars, such as the flat-spectrum radio quasars (FSRQs), are promising candidates to search for such emission. Because of the low fluxes due to large redshift, these sources are however challenging for the current generation of neutrino telescopes such as ANTARES and IceCube.
Aims. This paper proposes to exploit gravitational lensing effects to improve the sensitivity of neutrino telescopes to the intrinsic neutrino emission of distant blazars.
Methods. This strategy is illustrated with a search for cosmic neutrinos in the direction of four distant and gravitationally lensed blazars, using data collected from 2007 to 2012 by ANTARES. The magnification factor is estimated for each system assuming a singular isothermal profile for the lens. The neutrino event selection and statistical analysis are identical to the already published ANTARES search for neutrino point sources, which included a few (non-lensed) FSRQs.
Results. Based on ANTARES data, we derive upper limits on the intrinsic luminosity of the selected lensed sources. We obtain the strongest constraint from the lensed system B0218$+$357, providing a limit on the total neutrino luminosity of this FSRQ of $1.08\times 10^{46}\,\mathrm{erg}\,\mathrm{s}^{-1}$. This limit is about one order of magnitude lower than those obtained in the ANTARES standard point source search with non-lensed FSRQs, demonstrating the utility of the method.

[61]  arXiv:1407.8542 [pdf]
Title: Artificial_Micrometeorites
Authors: S. N. Dolya
Comments: 27 pages, 1 table
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Accelerator Physics (physics.acc-ph); Atmospheric and Oceanic Physics (physics.ao-ph)

An iron ball, a beryllium sphere and a tungsten tube segment with diameter twenty microns, are electrically charged while proton beam irradiating. These bodies are accelerated by the running pulse field in a spiral waveguide up to velocity: thirty kilometers per second. The accelerator, generating micrometeorites is placed at satellites on the Earth orbit. This article considers processes of penetration of micrometeorites into the Earth atmosphere. It is shown that micrometeorites evaporate at the height of one hundred kilometers-one hundred fifty kilometers from the surface of the Earth. A micrometeorite which is a segment of the beryllium tube equipped with a graphite cone in the head part is the very meteorite to reach the Earth surface without being broken.