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[1]  arXiv:1709.07442 [pdf, ps, other]
Title: X-ray to gamma-ray virial shock signal from the Coma cluster
Authors: Uri Keshet, Ido Reiss
Comments: 14 pages, 13 figures, comments welcome
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Following evidence for an east--west elongated virial ring around the Coma galaxy cluster in a $\sim220$ GeV VERITAS mosaic, we search for corresponding signatures in $>$GeV $\gamma$-rays from Fermi-LAT, and in soft, $\sim0.1$ keV X-rays from ROSAT. For the ring elongation and orientation inferred from VERITAS, we find a $3.4\sigma$ LAT excess, and detect ($>5\sigma$) the expected signature in ROSAT bands R1 and R1+R2. The significances of both LAT and ROSAT signals are maximal near the VERITAS ring parameters. The intensities of the ROSAT, Fermi, and VERITAS signals are consistent with the virial shock depositing $\sim0.3\%$ (with an uncertainty factor of $\sim3$) of its energy over a Hubble time in a nearly flat, $p\equiv - d\ln N_e/d\ln E\simeq 2.0$--$2.2$ spectrum of cosmic-ray electrons. The sharp radial profiles of the LAT and ROSAT signals suggest preferential accretion in the plane of the sky, as indicated by the distribution of neighboring large-scale structure. The X-ray signal gauges the compression of cosmic-rays as they are advected deeper into the cluster.

[2]  arXiv:1709.07447 [pdf, ps, other]
Title: The magnetorotational and Tayler instabilities in the pulsar magnetosphere
Authors: Vadim Urpin
Comments: 14 pages; has appeared in Journal of Astrophysics and Astronomy special issue on "Physics of Neutron Stars and Related Objects", celebrating the 75th birth-year of G.Srinivasan. arXiv admin note: substantial text overlap with arXiv:1401.2297
Journal-ref: JOAA, 38, 41 (2017)
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The magnetospheres around neutron stars should be very particular because of their strong magnetic field and rapid rotation. A study of the pulsar magnetospheres is of a crucial importance since it is the key issue to understand how energy inflow to the exterior is produced. In this paper, I discuss magnetohydrodynamic processes in the pulsar magnetosphere. I consider in detail the properties of magnetohydrodynamic waves that can exist in the magnetosphere and their instabilities.These instabilities lead to formation of magnetic structures and can be responsible for a short-term variability ofthe pulsar emission.

[3]  arXiv:1709.07448 [pdf, other]
Title: A new look at distances and velocities of neutron stars
Comments: Has appeared in Journal of Astrophysics and Astronomy special issue on 'Physics of Neutron Stars and Related Objects', celebrating the 75th birth-year of G. Srinivasan. Ten pages, nine figures
Journal-ref: J.Astrophys.Astr. (2017) 38:40
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR)

We take a fresh look at the determination of distances and velocities of neutron stars. The conversion of a parallax measurement into a distance, or distance probability distribution, has led to a debate quite similar to the one involving Cepheids, centering on the question whether priors can be used when discussing a single system. With the example of PSRJ0218+4232 we show that a prior is necessary to determine the probability distribution for the distance. The distance of this pulsar implies a gamma-ray luminosity larger than 10% of its spindown luminosity. For velocities the debate is whether a single Maxwellian describes the distribution for young pulsars. By limiting our discussion to accurate (VLBI) measurements we argue that a description with two Maxwellians, with distribution parameters sigma1=77 and sigma2=320 km/s, is significantly better. Corrections for galactic rotation, to derive velocities with respect to the local standards of rest, are insignificant.

[4]  arXiv:1709.07451 [pdf, other]
Title: Vacuum dynamics in the Universe versus a rigid $Λ=$const
Comments: Published in Int. J. Mod. Phys. A32 (2017) 1730014. arXiv admin note: text overlap with arXiv:1705.06723
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)

In this year, in which we celebrate 100 years of the cosmological term, $\Lambda$, in Einstein's gravitational field equations, we are still facing the crucial question whether $\Lambda$ is truly a fundamental constant or a mildly evolving dynamical variable. After many theoretical attempts to understand the meaning of $\Lambda$, and in view of the enhanced accuracy of the cosmological observations, it seems now mandatory that this issue should be first settled empirically before further theoretical speculations on its ultimate nature. In this work, we summarize the situation of some of these studies. Devoted analyses made recently show that the $\Lambda=$const. hypothesis, despite being the simplest, may well not be the most favored one. The overall fit to the cosmological observables $SNIa+BAO+H(z)+LSS+CMB$ singles out the class RVM of the "running" vacuum models, in which $\Lambda=\Lambda(H)$ is an affine power-law function of the Hubble rate. It turns out that the performance of the RVM as compared to the "concordance" $\Lambda$CDM model (with $\Lambda=$const.) is much better. The evidence in support of the RVM may reach $\sim 4\sigma$ c.l., and is bolstered with Akaike and Bayesian criteria providing strong evidence in favor of the RVM option. We also address the implications of this framework on the tension between the CMB and local measurements of the current Hubble parameter.

[5]  arXiv:1709.07452 [pdf, other]
Title: Low density, radiatively inefficient rotating-accretion flow onto a black hole
Comments: 16 pages, 17 figures, submitted to MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA); High Energy Astrophysical Phenomena (astro-ph.HE)

We study low-density axisymmetric accretion flows onto black holes (BHs) with two-dimensional hydrodynamical simulations, adopting the $\alpha$-viscosity prescription. When the gas angular momentum is low enough to form a rotationally supported disk within the Bondi radius ($R_{\rm B}$), we find a global steady accretion solution. The solution consists of a rotational equilibrium distribution at $r\sim R_{\rm B}$, where the density follows $\rho \propto (1+R_{\rm B}/r)^{3/2}$, surrounding a geometrically thick and optically thin accretion disk at the centrifugal radius, where thermal energy generated by viscosity is transported via strong convection. Physical properties of the inner solution agree with those expected in convection-dominated accretion flows (CDAF; $\rho \propto r^{-1/2}$). In the inner CDAF solution, the gas inflow rate decreases towards the center due to convection ($\dot{M}\propto r$), and the net accretion rate (including both inflows and outflows) is strongly suppressed by several orders of magnitude from the Bondi accretion rate $\dot{M}_{\rm B}$ The net accretion rate depends on the viscous strength, following $\dot{M}/\dot{M}_{\rm B}\propto (\alpha/0.01)^{0.6}$. This solution holds for low accretion rates of $\dot{M}_{\rm B}/\dot{M}_{\rm Edd}< 10^{-3}$ having minimal radiation cooling, where $\dot{M}_{\rm Edd}$ is the Eddington rate. In a hot plasma at the bottom ($r<10^{-3}~R_{\rm B}$), thermal conduction would dominate the convective energy flux. Since suppression of the accretion by convection ceases, the final BH feeding rate is found to be $\dot{M}/\dot{M}_{\rm B} \sim 10^{-3}-10^{-2}$. This rate is as low as $\dot{M}/\dot{M}_{\rm Edd} \sim 10^{-7}-10^{-6}$ inferred for SgrA$^*$ and the nuclear BHs in M31 and M87, and can explain the low luminosities in these sources, without invoking any feedback mechanism.

[6]  arXiv:1709.07455 [pdf, other]
Title: Most pseudo-bulges can be formed at later stages of major mergers
Comments: 25 pages, 16 figures, 11 tables
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Most giant spiral galaxies have pseudo or disk-like bulges that are considered to be the result of purely secular processes. This may challenge the hierarchical scenario predicting about one major merger per massive galaxy ($>$$3\times 10^{10} M_{\odot}$) since the last $\sim$ 9 billion years. Here we verify whether or not the association between pseudo-bulges and secular processes is irrevocable. Using GADGET2 N-body/SPH simulations, we have conducted a systematic study of remnants of major mergers which progenitors have been selected (1) to follow the gas richness-look back time relationship, and (2) with a representative distribution of orbits and spins in a cosmological frame. Analyzing the surface-mass density profile of both nearby galaxies and merger remnants with two components, we find that most of them show pseudo-bulges or bar dominated centers. Even if some orbits lead to classical bulges just after the fusion, the contamination by the additional gas that gradually accumulates to the center and forming stars later on, leads to remnants apparently dominated by pseudo-bulges. We also found that simple SPH simulations should be sufficient to form realistic spiral galaxies as remnants of ancient gas-rich mergers without need for specifically tuned feedback conditions. We then conclude that pseudo-bulges and bars in spiral galaxies are natural consequences of major mergers when they are realized in a cosmological context, i.e., with gas-rich progenitors as expected when selected in the distant Universe.

[7]  arXiv:1709.07457 [pdf, ps, other]
Title: Internal dark matter structure of the most massive galaxy clusters
Authors: Amandine M. C. Le Brun (1), Monique Arnaud (1), Gabriel W. Pratt (1), Romain Teyssier (2) ((1) CEA Saclay, (2) ICS Zürich)
Comments: 5 pages, 5 figures. Accepted by MNRAS Letters
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We investigate the evolution of the dark matter density profiles of the most massive galaxy clusters in the Universe. Using a `zoom-in' procedure on a large suite of cosmological simulations of total comoving volume of $3\,(h^{-1}\,\rm Gpc)^3$, we study the 25 most massive clusters in four redshift slices from $z\sim 1$ to the present. The minimum mass is $M_{500} > 5.5 \times 10^{14}$ M$_{\odot}$ at $z=1$. Each system has more than two million particles within $r_{500}$. Once scaled to the critical density at each redshift, the dark matter profiles within $r_{500}$ are strikingly similar from $z\sim1$ to the present day, exhibiting a low dispersion of 0.15 dex, and showing little evolution with redshift in the radial logarithmic slope and scatter. They have the running power law shape typical of the NFW-type profiles, and their inner structure, resolved to $3.8\,h^{-1}$ comoving kpc at $z=1$, shows no signs of converging to an asymptotic slope. Our results suggest that this type of profile is already in place at $z>1$ in the highest-mass haloes in the Universe, and that it remains exceptionally robust to merging activity.

[8]  arXiv:1709.07458 [pdf, other]
Title: Interferometric view of the circumstellar envelopes of northern FU Orionis-type stars
Comments: 17 pages, 11 figures; accepted for publication in A&A
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

FU Orionis-type objects are young, low-mass stars with large outbursts in visible light that last for several years or decades. They are thought to represent an evolutionary phase during the life of every young star when accretion from the circumstellar disk is enhanced during recurring time periods. These outbursts are able to rapidly build up the star while affecting the circumstellar disk and thus the ongoing or future planet formation. In many models infall from a circumstellar envelope seems to be necessary to trigger the outbursts. We observed the J=1$-$0 rotational transition of $^{13}$CO and C$^{18}$O towards eight northern FU Orionis-type stars (V1057 Cyg, V1515 Cyg, V2492 Cyg, V2493 Cyg, V1735 Cyg, V733 Cep, RNO 1B and RNO 1C) and derive temperatures and envelope masses and discuss the morphology and kinematics of the circumstellar material. We detected extended CO emission associated with all our targets. Smaller scale CO clumps were found to be associated with five objects with radii of 2000$-$5000 AU and masses of 0.02$-$0.5 $M_{\odot}$; these are clearly heated by the central stars. Three of these envelopes are also strongly detected in the 2.7 mm continuum. No central CO clumps were detected around V733 Cep and V710 Cas but there are many other clumps in their environments. Traces of outflow activity were observed towards V1735 Cyg, V733 Cep and V710 Cas. The diversity of the observed envelopes enables us to set up an evolutionary sequence between the objects. We find their evolutionary state to range from early, embedded Class I stage to late, Class II-type objects with very low-mass circumstellar material. The results reinforce the idea of FU Orionis-type stars as representatives of a transitory stage between embedded Class I young stellar objects and classical T-Tauri stars.

[9]  arXiv:1709.07459 [pdf, other]
Title: Modeling the effects of inhomogeneous aerosols on the hot Jupiter Kepler-7b's atmospheric circulation
Comments: Accepted to ApJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Motivated by the observational evidence of inhomogeneous clouds in exoplanetary atmospheres, we investigate how proposed simple cloud distributions can affect atmospheric circulations and infrared emission. We simulated temperatures and winds for the hot Jupiter Kepler-7b using a three-dimensional atmospheric circulation model that included a simplified aerosol radiative transfer model. We prescribed fixed cloud distributions and scattering properties based on results previously inferred from Kepler-7b optical phase curves, including inhomogeneous aerosols centered along the western terminator and hypothetical cases in which aerosols additionally extended across much of the planet's night side. In all cases, a strong jet capable of advecting aerosols from a cooler nightside to dayside was found to persist, but only at the equator. Colder temperatures at mid- and polar-latitudes might permit aerosol to form on the dayside without the need for advection. By altering the deposition and redistribution of heat, aerosols along the western terminator produced an asymmetric heating that effectively shifts the hottest spot further east of the sub-stellar point than expected for a uniform distribution. The addition of opaque high clouds on the nightside can partly mitigate this enhanced shift by retaining heat that contributes to warming west of the hotspot. These expected differences in infrared phase curves could place constraints on proposed cloud distributions and their infrared opacities for brighter hot Jupiters.

[10]  arXiv:1709.07462 [pdf, ps, other]
Title: The Baryonic Collapse Efficiency of Galaxy Groups in the RESOLVE and ECO Surveys
Comments: 23 pages, 16 figures, accepted for publication in ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We examine the z = 0 group-integrated stellar and cold baryonic (stars + cold atomic gas) mass functions (group SMF and CBMF) and the baryonic collapse efficiency (group cold baryonic to dark matter halo mass ratio) using the RESOLVE and ECO survey galaxy group catalogs and a galform semi-analytic model (SAM) mock catalog. The group SMF and CBMF fall off more steeply at high masses and rise with a shallower low-mass slope than the theoretical halo mass function (HMF). The transition occurs at group-integrated cold baryonic mass M_coldbary ~ 10^11 Msun. The SAM, however, has significantly fewer groups at the transition mass ~ 10^11 Msun and a steeper low-mass slope than the data, suggesting that feedback is too weak in low-mass halos and conversely too strong near the transition mass. Using literature prescriptions to include hot halo gas and potential unobservable galaxy gas produces a group BMF with slope similar to the HMF even below the transition mass. Its normalization is lower by a factor of ~2, in agreement with estimates of warm-hot gas making up the remaining difference. We compute baryonic collapse efficiency with the halo mass calculated two ways, via halo abundance matching (HAM) and via dynamics (extended all the way to three-galaxy groups using stacking). Using HAM, we find that baryonic collapse efficiencies reach a flat maximum for groups across the halo mass range of M_halo ~ 10^11.4-12 Msun, which we label "nascent groups." Using dynamics, however, we find greater scatter in baryonic collapse efficiencies, likely indicating variation in group hot-to-cold baryon ratios. Similarly, we see higher scatter in baryonic collapse efficiencies in the SAM when using its true groups and their group halo masses as opposed to friends-of-friends groups and HAM masses.

[11]  arXiv:1709.07464 [pdf, ps, other]
Title: Primordial perturbations with pre-inflationary bounce
Comments: 23 pages, 19 figures;
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)

Based on the effective field theory (EFT) of nonsingular cosmologies, we build a stable model, without the ghost and gradient instabilities, of bounce inflation (inflation is preceded by a cosmological bounce). We perform a full simulation for the evolution of scalar perturbation, and find that the perturbation spectrum has a large-scale suppression (as expected), which is consistent with the power deficit of the cosmic microwave background (CMB) TT-spectrum at low multipoles, but unexpectedly, it also shows itself one marked lower valley, which actually provides a better fit to the dip at multipole $l\sim 20$. The depth of valley is relevant with the physics around the bounce scale, which is model-dependent.

[12]  arXiv:1709.07465 [pdf, other]
Title: Cosmological implications of Primordial Black Holes
Comments: 20 pages, 9 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

The possibility that a relevant fraction of the dark matter might be comprised of Primordial Black Holes (PBHs) has been seriously reconsidered after LIGO's detection of a $\sim 30 M_{\odot}$ binary black holes merger. Despite the strong interest in the model, there is a lack of studies on possible cosmological implications and effects on cosmological parameters inference. We investigate correlations with the other standard cosmological parameters using cosmic microwave background observations, finding significant degeneracies, especially with the tilt of the primordial power spectrum and the sound horizon at radiation drag. However, these degeneracies can be greatly reduced with the inclusion of small scale polarization data. We also explore if PBHs as dark matter in simple extensions of the standard $\Lambda$CDM cosmological model induces extra degeneracies, especially between the additional parameters and the PBH's ones. Finally, we present cosmic microwave background constraints on the fraction of dark matter in PBHs, not only for monochromatic PBH mass distributions but also for popular extended mass distributions. Our results show that extended mass distribution's constraints are tighter, but also that a considerable amount of constraining power comes from the high-$\ell$ polarization data. Moreover, we constrain the shape of such mass distributions in terms of the correspondent constraints on the PBH mass fraction.

[13]  arXiv:1709.07467 [pdf, other]
Title: Primordial Black Holes as Dark Matter: Converting Constraints from Monochromatic to Extended Mass Distributions
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

The model in which Primordial Black Holes (PBHs) constitute a non-negligible fraction of the dark matter has (re)gained popularity after the first detections of binary black hole mergers. Most of the observational constraints to date have been derived assuming a single mass for all the PBHs, although some more recent works tried to generalize constraints to the case of extended mass functions. Here we derive a general methodology to obtain constraints for any PBH Extended Mass Distribution (EMD) and any observables in the desired mass range. Starting from those obtained for a monochromatic distribution, we convert them into constraints for EMDs by using an equivalent, effective mass $M_{\rm eq}$ that depends on the specific observable. We highlight how limits of validity of the PBH modelling affect the EMD parameter space. Finally, we present converted constraints on the total abundance of PBH from microlensing, stellar distribution in ultra-faint dwarf galaxies and CMB accretion for Lognormal and Power Law mass distributions, finding that EMD constraints are generally stronger than monochromatic ones.

[14]  arXiv:1709.07476 [pdf, other]
Title: High-resolution Imaging of Transiting Extrasolar Planetary systems (HITEP). II. Lucky Imaging results from 2015 and 2016
Comments: 32 pages, 14 figures, 12 tables. The contents of online-only tables 9 and 10 are included in the arXiv source
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM); Solar and Stellar Astrophysics (astro-ph.SR)

The formation and dynamical history of hot Jupiters is currently debated, with wide stellar binaries having been suggested as a potential formation pathway. Additionally, contaminating light from both binary companions and unassociated stars can significantly bias the results of planet characterisation studies, but can be corrected for if the properties of the contaminating star are known. We search for binary companions to known transiting exoplanet host stars, in order to determine the multiplicity properties of hot Jupiter host stars. We also characterise unassociated stars along the line of sight, allowing photometric and spectroscopic observations of the planetary system to be corrected for contaminating light. We analyse lucky imaging observations of 97 Southern hemisphere exoplanet host stars, using the Two Colour Instrument on the Danish 1.54m telescope. For each detected companion star, we determine flux ratios relative to the planet host star in two passbands, and measure the relative position of the companion. The probability of each companion being physically associated was determined using our two-colour photometry. A catalogue of close companion stars is presented, including flux ratios, position measurements, and estimated companion star temperature. For companions that are potential binary companions, we review archival and catalogue data for further evidence. For WASP-77AB and WASP-85AB, we combine our data with historical measurements to determine the binary orbits, showing them to be moderately eccentric and inclined to the line of sight and planetary orbital axis. Combining our survey with the similar Friends of Hot Jupiters survey, we conclude that known hot Jupiter host stars show a deficit of high mass stellar companions compared to the field star population; however, this may be a result of the biases in detection and target selection by ground-based surveys.

[15]  arXiv:1709.07479 [pdf, other]
Title: Primordial non-Gaussianity and power asymmetry with quantum gravitational effects in loop quantum cosmology
Comments: revtex4, one figure and no tables
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)

Loop quantum cosmology (LQC) provides a resolution of the classical big bang singularity in the deep Planck era. The evolution, prior to the usual slow-roll inflation, naturally generates excited states at the onset of the slow-roll inflation. It is expected that these quantum gravitational effects could leave its fingerprints on the primordial perturbation spectrum and non-Gaussianity, and lead to some observational evidences in the cosmic microwave background (CMB). While the impact of the quantum effects on the primordial perturbation spectrum has been already studied and constrained by current data, in this paper we continue studying such effects on the non-Gaussianity of the primordial curvature perturbations. In this paper, we present detailed and analytical calculations of the non-Gaussianity and show explicitly that the corrections due to quantum effects are in the same magnitude of the slow-roll parameters in the observable scales and thus are well within current observational constraints. Despite this, we show that the non-Gaussianity in the squeezed limit can be enhanced at superhorizon scales and further, these effects may yield a large statistical anisotropy on the power spectrum through the Erickcek-Kamionkowski-Carroll mechanism.

[16]  arXiv:1709.07489 [pdf, other]
Title: A Radio Relic and a Search for the Central Black Hole in the Abell 2261 Brightest Cluster Galaxy
Comments: 12 pages, 9 figures, submitted to ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present VLA images and HST/STIS spectra of sources within the center of the brightest cluster galaxy (BCG) in Abell 2261. These observations were obtained to test the hypothesis that its extremely large, flat core reflects the ejection of its supermassive black hole. Spectra of three of the four most luminous "knots" embedded in the core were taken to test whether one may represent stars bound to a displaced massive black hole. The three knots have radial velocity offsets dV < ~150 km/s from the BCG. Knots 2 and 3 show kinematics, colors, and stellar masses consistent with infalling low-mass galaxies or larger stripped cluster members. Large errors in the stellar velocity dispersion of Knot 1, however, mean that we cannot rule out the hypothesis that it hosts a high-mass black hole. A2261-BCG has a compact, relic radio-source offset by 6.5 kpc (projected) from the optical core's center, but no active radio core that would pinpoint the galaxy's central black hole to a tight 10 GHz flux limit <3.6 uJy. Its spectrum and morphology are suggestive of an active galactic nucleus that switched off >48 Myr ago, with an equipartition condition magnetic field of 15 uG. These observations are still consistent with the hypothesis that the nuclear black hole has been ejected from its core, but the critical task of locating the supermassive black hole or demonstrating that A2261-BCG lacks one remains to be done.

[17]  arXiv:1709.07519 [pdf, other]
Title: Combining angular differential imaging and accurate polarimetry with SPHERE/IRDIS to characterize young giant exoplanets
Comments: 16 pages, 8 figures, 2 tables
Journal-ref: Techniques and Instrumentation for Detection of Exoplanets VIII, Proc. of SPIE Vol. 10400, 1040015 (2017)
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)

Young giant exoplanets emit infrared radiation that can be linearly polarized up to several percent. This linear polarization can trace: 1) the presence of atmospheric cloud and haze layers, 2) spatial structure, e.g. cloud bands and rotational flattening, 3) the spin axis orientation and 4) particle sizes and cloud top pressure. We introduce a novel high-contrast imaging scheme that combines angular differential imaging (ADI) and accurate near-infrared polarimetry to characterize self-luminous giant exoplanets. We implemented this technique at VLT/SPHERE-IRDIS and developed the corresponding observing strategies, the polarization calibration and the data-reduction approaches. By combining ADI and polarimetry we can characterize planets that can be directly imaged with a very high signal-to-noise ratio. We use the IRDIS pupil-tracking mode and combine ADI and principal component analysis to reduce speckle noise. We take advantage of IRDIS' dual-beam polarimetric mode to eliminate differential effects that severely limit the polarimetric sensitivity (flat-fielding errors, differential aberrations and seeing), and thus further suppress speckle noise. To correct for instrumental polarization effects, we apply a detailed Mueller matrix model that describes the telescope and instrument and that has an absolute polarimetric accuracy $\leq0.1\%$. Using this technique we have observed the planets of HR 8799 and the (sub-stellar) companion PZ Tel B. Unfortunately, we do not detect a polarization signal in a first analysis. We estimate preliminary $1\sigma$ upper limits on the degree of linear polarization of $\sim1\%$ and $\sim0.1\%$ for the planets of HR 8799 and PZ Tel B, respectively. The achieved sub-percent sensitivity and accuracy show that our technique has great promise for characterizing exoplanets through direct-imaging polarimetry.

[18]  arXiv:1709.07521 [pdf, other]
Title: Topological analysis of nuclear pasta phases
Comments: 13 pages, 13 figures
Journal-ref: Phys. Rev. C 96, 025803 (2017)
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

In this paper the analysis of the result of numerical simulations of pasta phases using algebraic topology methods is presented. These considerations suggest that some phases can be further split into (sub)phases and therefore should be more refined in numerical simulations. The results presented in the paper can also be used to relate the Euler characteristic from numerical simulations to the geometry of the phases. The Betti numbers are used as they provide finer characterization of the phases. It is also shown that different boundary conditions give different outcomes.

[19]  arXiv:1709.07539 [pdf, other]
Title: Radiation pressure in super star cluster formation
Comments: 20 pages, 16 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA)

The physics of star formation at its extreme, in the nuclei of the largest and densest star clusters in the universe - potential massive black hole nurseries - has for decades eluded scrutiny. Spectroscopy of these systems has been scarce, whereas theoretical claims have been made that radiation pressure on dust grains somehow inhibits star formation. Here, we harness an accelerated Monte Carlo radiation transport scheme to report a radiation hydrodynamical simulation of super star cluster formation in turbulent clouds. We find that radiation pressure reduces the global star formation efficiency by 30-35%, and the star formation rate by 15-50%, both relative to a radiation-free control run. Overall, radiation pressure is ineffective in limiting the gas supply for star formation and the final stellar mass of the most massive cluster is $\sim 1.3\times10^6\,M_\odot$. The limited impact as compared to that implied by idealized theoretical models is attributed to a radiation-matter anti-correlation in the supersonically turbulent, gravitationally collapsing medium. In isolated regions outside massive clusters, where the gas distribution is less disturbed, radiation pressure is more effective in limiting star formation. The resulting stellar density at the cluster core is $\ge 10^{8}\,M_{\odot}\,\textrm{pc}^{-3}$, with stellar velocity dispersion $\gtrsim 70\,\text{km}\,\text{s}^{-1}$. We conclude that the super star cluster nucleus is propitious to the formation of very massive stars via dynamical core collapse and stellar merging. We speculate that the very massive star may avoid the claimed catastrophic mass loss by continuing to accrete dense gas condensing from a gravitationally-confined ionized phase.

[20]  arXiv:1709.07554 [pdf]
Title: The terrestrial late veneer from core disruption of a lunar-sized impactor
Comments: Accepted for publication in Earth and Planetary Science Letters, 17 pages, 4 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Overabundances in highly siderophile elements (HSEs) of Earth's mantle can be explained by conveyance from a singular, immense (3000 km in a diameter) "Late Veneer" impactor of chondritic composition, subsequent to lunar formation and terrestrial core-closure. Such rocky objects of approximately lunar mass (about 0.01 M_E) ought to be differentiated, such that nearly all of their HSE payload is sequestered into iron cores. Here, we analyze the mechanical and chemical fate of the core of such a Late Veneer impactor, and trace how its HSEs are suspended - and thus pollute - the mantle. For the statistically most-likely oblique collision (about 45degree), the impactor's core elongates and thereafter disintegrates into a metallic hail of small particles (about 10 m). Some strike the orbiting Moon as sesquinary impactors, but most re-accrete to Earth as secondaries with further fragmentation. We show that a single oblique impactor provides an adequate amount of HSEs to the primordial terrestrial silicate reservoirs via oxidation of (<m-sized) metal particles with a hydrous, pre-impact, early Hadean Earth.

[21]  arXiv:1709.07562 [pdf, ps, other]
Title: 3xmm j181923.7$-$170616: an x-ray binary with a 408s pulsar
Comments: 15 pages, 7 figures, Published in the Astrophysical Journal
Journal-ref: The Astrophysical Journal, 847:44 (9pp), 2017 September 20
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We carry out a dedicated study of 3XMM J181923.7$-$170616\ with an approximate pulsation period of 400~s using the XMM-Newton and Swift observations spanning across nine years. We have refined the period of the source to 407.904(7) s (at epoch MJD 57142) and determined a period derivative limit of $\dot{P}{\leq} 5.9\pm 5.4\times 10^{-9} s s^{-1}$ ($1\sigma$). The source radiates hard, persistent X-ray emission during the observation epochs, which is best described by an absorbed \powerlaw\ model ($\Gamma \sim 0.2$--0.8) plus faint Fe lines at 6.4 keV and 6.7 keV. The X-ray flux revealed a variation within a factor of 2, along with a spectral hardening as the flux increased. The pulse shape is sinusoid-like and the spectral properties of different phases do not present significant variation. The absorption N$_H$ $\sim 1.3\times 10^{22} cm^{-2}$ is similar to the total Galactic hydrogen column density along the direction, indicating that it is a distant source. A search for the counterpart in optical and near-infrared surveys reveals a low mass K-type giant, while the existence of a Galactic OB supergiant is excluded. A symbiotic X-ray binary is the favored nature of 3XMM J181923.7$-$170616 and can essentially explain the low luminosity of ${2.78\times 10^{34} d_{10}^{2} erg s^{-1}}$, slow pulsation, hard X-ray spectrum, and possible K3~III companion. An alternative explanation of the source is a persistent Be/X-ray binary with a companion star no earlier than B3-type.

[22]  arXiv:1709.07577 [pdf, other]
Title: The multiphase circumgalactic medium traced by low metal ions in EAGLE zoom simulations
Comments: 26 pages, 19 figures, submitted to MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We explore the circumgalactic metal content traced by commonly observed low ion absorbers, including C II, Si II, Si III, Si IV, and Mg II. We use a set of cosmological hydrodynamical zoom simulations run with the EAGLE model and including a non-equilibrium ionization and cooling module that follows 136 ions. The simulations of z~0.2 L* (M_200=10^11.7-10^12.3 Msol) haloes hosting star-forming galaxies and group-sized (M_200=10^12.7-10^13.3 Msol) haloes hosting mainly passive galaxies reproduce key trends observed by the COS-Halos survey-- low ion column densities show 1) little dependence on galaxy specific star formation rate, 2) a patchy covering fraction indicative of 10^4 K clouds with a small volume filling factor, and 3) a declining covering fraction as impact parameter increases from 20-160 kpc. Simulated Si II, Si III, Si IV, C II, and C III column densities show good agreement with observations, while Mg II is under-predicted. Low ions trace a significant metal reservoir, ~10^8 Msol, residing primarily at 10-100 kpc from star-forming and passive central galaxies. These clouds tend to flow inwards and most will accrete onto the central galaxy within the next several Gyr, while a small fraction are entrained in strong outflows. A two-phase structure describes the inner CGM (<0.5 R_200) with low-ion metal clouds surrounded by a hot, ambient medium. This cool phase is separate from the O VI observed by COS-Halos, which arises from the outer CGM (>0.5 R_200) tracing virial temperature gas around L* galaxies. Physical parameters derived from standard photo-ionization modelling of observed column densities (e.g. aligned Si II/Si III absorbers) are validated against our simulations. Our simulations therefore support previous ionization models indicating that cloud covering factors decline while densities and pressures show little variation with increasing impact parameter.

[23]  arXiv:1709.07579 [pdf, ps, other]
Title: Correlation between the luminosity and spin-period changes during outbursts of 12 Be binary pulsars observed by the MAXI/GSC and the Fermi/GBM
Comments: 21 pages, 9 figures, accepted for publication in PASJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

To observationally study spin-period changes of accreting pulsars caused by the accretion torque, the present work analyzes X-ray light curves of 12 Be binary pulsars obtained by the MAXI/GSC all-sky survey and their pulse periods measured by the Fermi/GBM pulsar project, both covering more than 6 years from 2009 August to 2016 March. The 12 objects were selected because they are accompanied by clear optical identification, and accurate measurements of surface magnetic fields. The luminosity $L$ and the spin-frequency derivatives $\dot{\nu}$, measured during large outbursts with $L\gtrsim 1\times 10^{37}$ erg s$^{-1}$, were found to approximately follow the theoretical relations in the accretion torque models, represented by $\dot{\nu} \propto L^{\alpha}$ ($\alpha\simeq 1$), and the coefficient of proportionality between $\dot{\nu}$ and $L^{\alpha}$, agrees, within a factor of $\sim 3$, with that proposed by Ghosh & Lamb (1979). In the course of the present study, the orbital elements of several sources were refined.

[24]  arXiv:1709.07587 [pdf, other]
Title: Carbon Abundances in Starburst Galaxies of the Local Universe
Comments: Accepted for publication in ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA)

The cosmological origin of carbon, the fourth most abundant element in the Universe, is not well known and matter of heavy debate. We investigate the behavior of C/O to O/H in order to constrain the production mechanism of carbon. We measured emission-line intensities in a spectral range from 1600 to 10000 \AA\ on Space Telescope Imaging Spectrograph (STIS) long-slit spectra of 18 starburst galaxies in the local Universe. We determined chemical abundances through traditional nebular analysis and we used a Markov Chain Monte Carlo (MCMC) method to determine where our carbon and oxygen abundances lie in the parameter space. We conclude that our C and O abundance measurements are sensible. We analyzed the behavior of our sample in the [C/O] vs. [O/H] diagram with respect to other objects such as DLAs, neutral ISM measurements, and disk and halo stars, finding that each type of object seems to be located in a specific region of the diagram. Our sample shows a steeper C/O vs. O/H slope with respect to other samples, suggesting that massive stars contribute more to the production of C than N at higher metallicities, only for objects where massive stars are numerous; otherwise intermediate-mass stars dominate the C and N production.

[25]  arXiv:1709.07596 [pdf, other]
Title: Neutral hydrogen (HI) gas content of galaxies at $z \approx 0.32$
Comments: 16 pages, 14 figures, accepted for publication in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We use observations made with the Giant Metrewave Radio Telescope (GMRT) to probe the neutral hydrogen (HI) gas content of field galaxies in the VIMOS VLT Deep Survey (VVDS) 14h field at $z \approx 0.32$. Because the HI emission from individual galaxies is too faint to detect at this redshift, we use an HI spectral stacking technique using the known optical positions and redshifts of the 165 galaxies in our sample to co-add their HI spectra and thus obtain the average HI mass of the galaxies. Stacked HI measurements of 165 galaxies show that 95 per cent of the neutral gas is found in blue, star-forming galaxies. Among these galaxies, those having lower stellar mass are more gas-rich than more massive ones. We apply a volume correction to our HI measurement to evaluate the HI gas density at $z \approx 0.32$ as $\Omega_{HI}=(0.50\pm0.18) \times 10^{-3}$ in units of the cosmic critical density. This value is in good agreement with previous results at z < 0.4, suggesting no evolution in the neutral hydrogen gas density over the last $\sim 4$ Gyr. However the $z \approx 0.32$ gas density is lower than that at $z \sim 5$ by at least a factor of two.

[26]  arXiv:1709.07619 [pdf, other]
Title: The FRIGG project: From intermediate galactic scales to self-gravitating cores
Comments: accepted for publication in A&A
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Abridged. Understanding the detailed structure of the interstellar gas is essential for our knowledge of the star formation process. The small-scale structure of the interstellar medium (ISM) is a direct consequence of the galactic scales and making the link between the two is essential. We perform adaptive mesh simulations that aim to bridge the gap between the intermediate galactic scales and the self-gravitating prestellar cores. For this purpose we use stratified supernova regulated ISM magneto-hydrodynamical (MHD) simulations at the kpc scale to set up the initial conditions. We then zoom, performing a series of concentric uniform refinement and then refining on the Jeans length for the last levels. This allows us to reach a spatial resolution of a few $10^{-3}$ pc. The cores are identified using a clump finder and various criteria based on virial analysis. Their most relevant properties are computed and, due to the large number of objects formed in the simulations, reliable statistics are obtained. The cores properties show encouraging agreements with observations. The mass spectrum presents a clear powerlaw at high masses with an exponent close to $\simeq -1.3$ and a peak at about 1-2 $M_\odot$. The velocity dispersion and the angular momentum distributions are respectively a few times the local sound speed and a few $10^{-2}$ pc km s$^{-1}$. We also find that the distribution of thermally supercritical cores present a range of magnetic mass-to-flux over critical mass-to-flux ratio which typically ranges between $\simeq$0.3 and 3.

[27]  arXiv:1709.07622 [pdf, ps, other]
Title: Hot-cold plasma transition region: collisionless case
Comments: 7 pages, 9 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Plasma Physics (physics.plasm-ph); Space Physics (physics.space-ph)

We study processes at the transition region between hot (rare) and cold (dense) plasma in the collisionless regime. We use a 3-dimensional electromagnetic particle-in-cell (3-D PIC) relativistic code. Motivated by the transition region in the solar atmosphere the temperature and density ratio of the plasmas is chosen as 100 and 0.01, respectively. For better understanding of studied processes we make two types of computations: a) without any interactions among plasma particles (free expansion) and b) with the full electromagnetic interactions. In both the cases we found that the flux of cold plasma electrons and protons from colder plasma to hotter one dominates over the flux of hot plasma electrons and protons in the opposite direction. Thus, the plasma in the hotter part of the system becomes colder and denser during time evolution. In the case without any interactions among particles the cold plasma electrons and protons freely penetrate into the hot plasma. But, the cold plasma electrons are faster than cold plasma protons and therefore they penetrate deeper into the hotter part of the system than the protons. Thus, the cooling of the electron and proton components of the plasma in the hotter part of the system is different. On the other hand, in the case with the electromagnetic interactions, owing to the plasma property, which tries to keep the total electric current constant everywhere (close to zero in our case), the cold plasma electrons penetrate into the hotter part of the system together with the cold plasma protons. The plasma waves generated at the transition region during these processes reduce the number of electrons escaping from the hot plasma into the colder one. Therefore these waves support a temperature jump between hot and cold plasma.

[28]  arXiv:1709.07636 [pdf]
Title: Formation of Double Neutron Stars, Millisecond Pulsars and Double Black Holes
Comments: Has appeared in Journal of Astrophysics and Astronomy special issue on 'Physics of Neutron Stars and Related Objects', celebrating the 75th birth year of G. Srinivasan
Journal-ref: J.Astrophys.Astr.(September 2017)38:45
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The 1982 model for the formation of the Hulse-Taylor binary radio pulsar PSR B1913+16 is described, which since has become the standard model for the formation of double neutron stars, confirmed by the 2003 discovery of the double pulsar system PSR J0737-3039AB. A brief overview is given of the present status of our knowledge of the double neutron stars, of which 15 systems are presently known. The binary-recycling model for the formation of millisecond pulsars is described, as put forward independently by Alpar et al. (1982), Radhakrishnan and Srinivasan (1982) and Fabian et al. (1983). This now is the standard model for the formation of these objects, confirmed by the discovery in 1998 of the accreting millisecond X-ray pulsars. It is noticed that the formation process of close double black holes has analogies to that of close double neutron stars, extended to binaries of larger iinitial component masses, although there are also considerable differences in the physics of the binary evolution at these larger masses.

[29]  arXiv:1709.07651 [pdf, other]
Title: KiDS-450: Cosmological Constraints from Weak Lensing Peak Statistics-I: Inference from Analytical Prediction of high Signal-to-Noise Ratio Convergence Peaks
Comments: 19 pages, 12 figures. Submitted to MNRAS
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

This paper is the first of a series of papers constraining cosmological parameters with weak lensing peak statistics using $\sim 450~\rm deg^2$ of imaging data from the Kilo Degree Survey (KiDS-450). We measure high signal-to-noise ratio (SNR: $\nu$) weak lensing convergence peaks in the range of $3<\nu<5$, and employ theoretical models to derive expected values. These models are validated using a suite of simulations. We take into account two major systematic effects, the boost factor and the effect of baryons on the mass-concentration relation of dark matter haloes. In addition, we investigate the impacts of other potential astrophysical systematics including the projection effects of large scale structures, intrinsic galaxy alignments, as well as residual measurement uncertainties in the shear and redshift calibration. Assuming a flat $\Lambda$CDM model, we find constraints for $S_{\rm 8}=\sigma_{\rm 8}(\Omega_{\rm m}/0.3)^{0.5}=0.746^{+0.046}_{-0.107}$ according to the degeneracy direction of the cosmic shear analysis and $\Sigma_{\rm 8}=\sigma_{\rm 8}(\Omega_{\rm m}/0.3)^{0.38}=0.696^{+0.048}_{-0.050}$ based on the derived degeneracy direction of our high-SNR peak statistics. The difference between the power index of $S_{\rm 8}$ and in $\Sigma_{\rm 8}$ indicates that combining the two probes has the potential to break the degeneracy in $\sigma_{\rm 8}$ and $\Omega_{\rm m}$. Our results are consistent with the cosmic shear tomographic correlation analysis of the same dataset and $\sim 2\sigma$ lower than the Planck 2016 results.

[30]  arXiv:1709.07653 [pdf, other]
Title: Effect of the diffusion parameters on the observed gamma-ray spectrum of sources and their contribution to the local all-electron spectrum: the EDGE code
Comments: Submitted to APh
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The positron excess measured by PAMELA and AMS can only be explained if there is one or several sources injecting them. Moreover, at the highest energies, it requires the presence of nearby ($\sim$hundreds of parsecs) and middle age (maximum of $\sim$hundreds of kyr) sources. Pulsars, as factories of electrons and positrons, are one of the proposed candidates to explain the origin of this excess. To calculate the contribution of these sources to the electron and positron flux at the Earth, we developed EDGE (Electron Diffusion and Gamma rays to the Earth), a code to treat the propagation of electrons and compute their diffusion from a central source with a flexible injection spectrum. Using this code, we can derive the source's gamma-ray spectrum, spatial extension, the all-electron density in space, the electron and positron flux reaching the Earth and the positron fraction measured at the Earth. We present in this paper the foundations of the code and study how different parameters affect the gamma-ray spectrum of a source and the electron flux measured at the Earth. We also studied the effect of several approximations usually performed in these studies.

[31]  arXiv:1709.07669 [pdf, ps, other]
Title: Impact of Rotation on Quark-Hadron Hybrid Stars
Authors: Tomoki Endo
Comments: Quarks and Compact Stars 2017
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Many recent observations give restrictions to the equation of state (EOS) for high-density matter. Theoretical studies are needed to try to elucidate these EOSs at high density and/or temperature. With the many known rapidly rotating neutron stars, e.g., pulsars, several theoretical studies have tried to take into account the effects of rotation. In our study of these systems, we find that one of our EOSs is consistent with recent observation, whereas the other is inconsistent.

[32]  arXiv:1709.07678 [pdf, other]
Title: KiDS-450: Cosmological Constraints from Weak Lensing Peak Statistics - II: Inference from Shear Peaks in N-body Simulations
Comments: 18 pages, 15 figures, submitted to MNRAS
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We study the statistics of peaks in a weak lensing reconstructed mass map of the first 450 square degrees of the Kilo Degree Survey. The map is computed with aperture masses directly applied to the shear field with an NFW-like compensated filter. We compare the peak statistics in the observations with that of simulations for various cosmologies to constrain the cosmological parameter $S_8 = \sigma_8 \sqrt{\Omega_{\rm m}/0.3}$, which probes the ($\Omega_{\rm m}, \sigma_8$) plane perpendicularly to its main degeneracy. We estimate $S_8=0.750\pm0.059$, using peaks in the signal-to-noise range $0 \leq {\rm S/N} \leq 4$, and accounting for various systematics, such as multiplicative shear bias, mean redshift bias, baryon feedback, intrinsic alignment, and shear-position coupling. These constraints are $\sim25\%$ tighter than the constraints from the high significance peaks alone ($3 \leq {\rm S/N} \leq 4$) which typically trace single-massive halos. This demonstrates the gain of information from low-S/N peaks which correspond to the projection of several small-mass halos along the line-of-sight. Our results are in good agreement with the tomographic shear two-point correlation function measurement in KiDS-450. Combining shear peaks with non-tomographic measurements of the shear two-point correlation functions yields an $\sim20\%$ improvement in the uncertainty on $S_8$ compared to the shear two-point correlation functions alone, highlighting the great potential of peaks as a cosmological probe.

[33]  arXiv:1709.07679 [pdf, ps, other]
Title: Calvera: A low-mass strangeon star torqued by debris disk?
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Calvera is a $59\,\mathrm{ms}$ isolated pulsar, being unique due to its non-detection in radio, optical and gamma-rays but the purely thermal emission in soft X-rays. It is suggested that Calvera could be an ordinary middle-aged pulsar with significant magnetospheric activity at a large distance. Alternatively, it is proposed in this paper that Calvera is a low-mass strangeon star with inactive magnetosphere (dead). In this scenario, we jointly fit the spectra obtained by the {\it XMM-Newton} Observatory and the {\it Chandra} X-ray Observatory with the strangeon star atmosphere model. The spectral model is successful in explaining the radiation properties of Calvera and X-ray Dim Isolated Neutron Stars, both showing similar observation features. Within the dead pulsar picture, Calvera might be of high temperature at $0.67\,\mathrm{keV}$, possessing a small magnetic field $B\la10^{11}\,\mathrm{G}$ and a small stellar radius $R\la4\,\mathrm{km}$ and is probably braked by the fall-back disk accretion. Future advanced facilities may provide unique opportunities to know the real nature of Calvera.

[34]  arXiv:1709.07693 [pdf, other]
Title: The Saturnian Kilometric Radiation before the Cassini Grand Finale
Authors: Laurent Lamy
Comments: Refereed article; Proceedings of the 8th International Workshop on Planetary, Solar and Heliospheric Radio Emissions (PRE VIII), Seggauberg, Austria, Oct. 25-27, 2016
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

The Saturnian Kilometric Radiation (SKR) is radiated from the auroral regions surrounding the kronian magnetic poles, above the ionosphere up to a few planetary radii. It directly compares to the auroral radio emissions emanating from other planetary magnetospheres such as the Earth and the giant planets. Our knowledge on SKR relied on remote observations of Voyager (flybys in 1980 and 1981) and Ulysses (distant observations in the 1990s) until Cassini started to orbit Saturn in 2004. Since then, it has been routinely observed from a large set of remote locations, but also in situ for the first time at a planet other than Earth. This article reviews the state of the art of SKR average remote properties, the first insights brought by in situ passes within its source region, together with some remaining questions before the Cassini Grand Finale and its close-in polar orbits.

[35]  arXiv:1709.07694 [pdf, ps, other]
Title: Kinetic temperature of massive star-forming molecular clumps measured with formaldehyde. III. The Orion Molecular Cloud 1
Comments: Accepted for publication in A&A
Subjects: Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)

We mapped the kinetic temperature structure of the Orion molecular cloud 1 with para-H2CO(303-202, 322-221, and 321-220) using the APEX 12m telescope. This is compared with the temperatures derived from the ratio of the NH3(2,2)/(1,1) inversion lines and the dust emission. Using the RADEX non-LTE model, we derive the gas kinetic temperature modeling the measured averaged line ratios of para-H2CO 322-221/303-202 and 321-220/303-202. The gas kinetic temperatures derived from the para-H2CO line ratios are warm, ranging from 30 to >200 K with an average of 62 K at a spatial density of 10$^5$ cm$^{-3}$. These temperatures are higher than those obtained from NH3(2,2)/(1,1) and CH3CCH(6-5) in the OMC-1 region. The gas kinetic temperatures derived from para-H2CO agree with those obtained from warm dust components measured in the mid infrared (MIR), which indicates that the para-H2CO(3-2) ratios trace dense and warm gas. The cold dust components measured in the far infrared (FIR) are consistent with those measured with NH3(2,2)/(1,1) and the CH3CCH(6-5) line series. With dust at MIR wavelengths and para-H2CO(3-2) on one side and dust at FIR wavelengths, NH3(2,2)/(1,1), and CH3CCH(6-5) on the other, dust and gas temperatures appear to be equivalent in the dense gas of the OMC-1 region, but provide a bimodal distribution, one more directly related to star formation than the other. The non-thermal velocity dispersions of para-H2CO are positively correlated with the gas kinetic temperatures in regions of strong non-thermal motion (Mach number >2.5) of the OMC-1, implying that the higher temperature traced by para-H2CO is related to turbulence on a 0.06 pc scale. Combining the temperature measurements with para-H2CO and NH3(2,2)/(1,1) line ratios, we find direct evidence for the dense gas along the northern part of the OMC-1 10 km s$^{-1}$ filament heated by radiation from the central Orion nebula.

[36]  arXiv:1709.07702 [pdf, other]
Title: Evidence for disks at an early stage in class 0 protostars?
Authors: M. Gerin (1), J. Pety (2,1), B. Commercon (3), A. Fuente (4), J. Cernicharo (5), N. Marcelino (5), A. Ciardi (1), D. C. Lis (1), E. Roueff (1), H.A. Wootten (6), E. Chapillon (7,2) ((1) LERMA, (2) IRAM, (3) CRAL, (4) OAN-IGN, (5) ICMM-CSIC, (6) NRAO, (7) LAB)
Comments: 8 pages, 10 PDF figures. Accepted for publication in A&A. Uses aa and natbib latex macros
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

The formation epoch of protostellar disks is debated because of the competing roles of rotation, turbulence, and magnetic fields in the early stages of low-mass star formation. Magnetohydrodynamics simulations of collapsing cores predict that rotationally supported disks may form in strongly magnetized cores through ambipolar diffusion or misalignment between the rotation axis and the magnetic field orientation. Detailed studies of individual sources are needed to cross check the theoretical predictions. We present 0.06-0.1" resolution images at 350 GHz toward B1b-N and B1b-S, which are young class 0 protostars, possibly first hydrostatic cores. The images have been obtained with ALMA, and we compare these data with magnetohydrodynamics simulations of a collapsing turbulent and magnetized core. The submillimeter continuum emission is spatially resolved by ALMA. Compact structures with optically thick 350 GHz emission are detected toward both B1b-N and B1b-S, with 0.2 and 0.35" radii (46 and 80 au at the Perseus distance of 230 pc), within a more extended envelope. The flux ratio between the compact structure and the envelope is lower in B1b-N than in B1b-S, in agreement with its earlier evolutionary status. The size and orientation of the compact structure are consistent with 0.2" resolution 32 GHz observations obtained with the Very Large Array as a part of the VANDAM survey, suggesting that grains have grown through coagulation. The morphology, temperature, and densities of the compact structures are consistent with those of disks formed in numerical simulations of collapsing cores. Moreover, the properties of B1b-N are consistent with those of a very young protostar, possibly a first hydrostatic core. These observations provide support for the early formation of disks around low-mass protostars.

[37]  arXiv:1709.07704 [pdf, other]
Title: Search for varying constants of nature from astronomical observation of molecules
Authors: Wim Ubachs
Comments: Contribution to Workshop "High Performance Clocks in Space" at the International Space Science Institute, Bern 2015
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

The status of searches for possible variation in the constants of nature from astronomical observation of molecules is reviewed, focusing on the dimensionless constant representing the proton-electron mass ratio $\mu=m_p/m_e$. The optical detection of H$_2$ and CO molecules with large ground-based telescopes (as the ESO-VLT and the Keck telescopes), as well as the detection of H$_2$ with the Cosmic Origins Spectrograph aboard the Hubble Space Telescope is discussed in the context of varying constants, and in connection to different theoretical scenarios. Radio astronomy provides an alternative search strategy bearing the advantage that molecules as NH$_3$ (ammonia) and CH$_3$OH (methanol) can be used, which are much more sensitive to a varying $\mu$ than diatomic molecules. Current constraints are $|\Delta\mu/\mu| < 5 \times 10^{-6}$ for redshift $z=2.0-4.2$, corresponding to look-back times of 10-12.5 Gyrs, and $|\Delta\mu/\mu| < 1.5 \times 10^{-7}$ for $z=0.88$, corresponding to half the age of the Universe (both at 3$\sigma$ statistical significance). Existing bottlenecks and prospects for future improvement with novel instrumentation are discussed.

[38]  arXiv:1709.07706 [pdf, other]
Title: The kilo Hertz quasi-periodic oscillations in neutron star low-mass X-ray binaries as tori oscillation modes. I
Comments: 9 pages, 5 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc)

There have been many efforts to explain the dynamical mechanisms behind the phenomenology of quasi-periodic oscillations (QPOs) seen in the X-ray light curves of low-mass X-ray binaries. Up to now, none of the models can successfully explain all the frequencies observed in the power density spectrum of the light curve. Here we perform several hydrodynamic simulations of non-self-gravitating relativistic axisymmetric thick tori applied to the neutron star in the low-mass X-ray binary 4U 1636-53 and show how the observed oscillation modes triggered by different velocity perturbations give rise to a set of variability features similar to what we see in the observational X-ray data. When we match pairs of frequencies from the simulations of constant angular momentum ($l$) tori with the observed kilo Hertz QPOs, we find that certain combinations of frequencies lie on top of the observed relation, provided we assume a smaller mass for the neutron star than is generally assumed. However, constant-$l$ tori cannot match the entire range of frequencies observed for 4U 1636-53 due to physical constraints set by the torus size. We show that our model is consistent with the observed shift in QPO frequency that accompany state transitions of the accretion disk.

[39]  arXiv:1709.07717 [pdf, other]
Title: On the far-infrared metallicity diagnostics: applications to high-redshift galaxies
Comments: 10 pages, 7 figures, MNRAS in press
Subjects: Astrophysics of Galaxies (astro-ph.GA)

In an earlier paper we modeled the far-infrared emission from a star-forming galaxy using the photoionisation code CLOUDY and presented metallicity sensitive diagnostics based on far-infrared fine structure line ratios. Here, we focus on the applicability of the [OIII]88/[NII]122 microns line ratio as a gas phase metallicity indicator in high redshift submillimetre luminous galaxies. The [OIII]88/[NII]122 microns ratio is strongly dependent on the ionization parameter (which is related to the total number of ionizing photons) as well as the gas electron density. We demonstrate how the ratio of 88/$122 continuum flux measurements can provide a reasonable estimate of the ionization parameter while the availability of the [NII]205 microns line can constrain the electron density. Using the [OIII]88/[NII]122 microns line ratios from a sample of nearby normal and star-forming galaxies we measure their gas phase metallicities and find that their mass metallicity relation is consistent with the one derived using optical emission lines. Using new, previously unpublished, Herschel spectroscopic observations of key far-infrared fine structure lines of the z~3 galaxy HLSW-01 and additional published measurements of far-infrared fine structure lines of high-z submillimetre luminous galaxies we derive gas phase metallicities using their [OIII]88/[NII]122 microns line ratio. We find that the metallicities of these z~3 submm luminous galaxies are consistent with solar metallicities and that they appear to follow the mass-metallicity relation expected for z~3 systems.

[40]  arXiv:1709.07727 [pdf, other]
Title: Wide-field LOFAR-LBA power-spectra analyses: Impact of calibration, polarization leakage and ionosphere
Comments: 17 pages, 10 figures, submitted to MNRAS
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

Contamination due to foregrounds (Galactic and Extra-galactic), calibration errors and ionospheric effects pose major challenges in detection of the cosmic 21 cm signal in various Epoch of Reionization (EoR) experiments. We present the results of a pilot study of a field centered on 3C196 using LOFAR Low Band (56-70 MHz) observations, where we quantify various wide field and calibration effects such as gain errors, polarized foregrounds, and ionospheric effects. We observe a `pitchfork' structure in the 2D power spectrum of the polarized intensity in delay-baseline space, which leaks into the modes beyond the instrumental horizon (EoR/CD window). We show that this structure largely arises due to strong instrumental polarization leakage ($\sim 30\%$) towards CasA (21 kJy at 81 MHz, brightest source in northern sky), which is far away from primary field of view. We measure an extremely small ionospheric diffractive scale ($r_{\text{diff}} \sim 80\lambda \approx 400$ m at 60 MHz) towards CasA resembling pure Kolmogorov turbulence compared to $r_{\text{diff}} \sim 3 - 20$ km towards zenith at 150 MHz for typical ionospheric conditions. This is one of the smallest diffractive scales ever measured at these frequencies. Our work provides insights in understanding the nature of aforementioned effects and mitigating them in future Cosmic Dawn observations (e.g. with SKA) in the same frequency window.

[41]  arXiv:1709.07754 [pdf, ps, other]
Title: Kinematics and Structure of Star-forming Regions: Insights from Cold Collapse Models
Comments: 7 pages, 4 figures, accepted to MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)

The origin of the observed morphological and kinematic substructure of young star forming regions is a matter of debate. We offer a new analysis of data from simulations of globally gravitationally collapsing clouds of progenitor gas to answer questions about sub-structured star formation in the context of cold collapse. As a specific example, we compare our models to recent radial velocity survey data from the IN-SYNC survey of Orion and new observations of dense gas kinematics, and offer possible interpretations of kinematic and morphological signatures in the region. In the context of our model, we find the frequently-observed hub-filament morphology of the gas naturally arises during gravitational evolution, as well as the dynamically-distinct kinematic substructure of stars. We emphasize that the global and not just the local gravitational potential plays an important role in determining the dynamics of both clusters and filaments.

[42]  arXiv:1709.07793 [pdf, other]
Title: Cosmic Ray Acceleration by Relativistic Shocks: Limits and Estimates
Comments: Accepted for publication in Monthly Notices of the Royal Astronomical Society
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We examine limits to the energy to which cosmic rays can be accelerated by relativistic shocks, showing that acceleration of light ions as high as 100 EeV is unlikely. The implication of our estimates is that if ultra-high energy cosmic rays are accelerated by shocks, then those shocks are probably not relativistic.

[43]  arXiv:1709.07795 [pdf, other]
Title: An effective description of dark energy: from theory to phenomenology
Comments: PhD thesis, defended on June 27th,2017 with original title "Tests de coh\'erence de l'Univers et reliques cosmiques"
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)

In the last decades, a cosmological model that fits observations through a vast range of scales emerged. It goes under the name of ${\Lambda}$CDM. However, there are still challenging questions that remain unanswered by this model, such as what causes the observed accelerated expansion of the universe, and many alternatives have been proposed. This thesis concerns an approach to test such models known as "Effective Theory of Dark Energy" . It applies to all models where general relativity is modified by adding a single scalar degree of freedom, called "scalar-tensor theories". In Chapter 1 I summarise the most general class of such theories currently known, called "Degenerate higher-Order Scalar-Tensor" (DHOST) theories. In Chapter 2, I introduce the effective theory of dark energy. The inclusion of a general coupling between matter and the gravitational sector is the subject of Chapter 3. Chapter 4 analyses in details the stability of different classes of theories. Notably, I show that the most general class of theories free from instabilities reduces to the so-called Horndeski and beyond-Horndeski theories, up to a non minimal coupling to matter. Another goal of the thesis is to study the observable effects of deviations from ${\Lambda}$CDM. In Chapter 5, I consider the possibility of an interaction between dark matter and dark energy and I analyse the constraining power of future surveys on the free parameters of the theory. Chapter 6 focuses on the observational effects of theories where a kinetic mixing between matter and the scalar field exists. This gives a peculiar and potentially observable effect, namely the weakening of gravity at large scale structure scales.

[44]  arXiv:1709.07800 [pdf, other]
Title: Stellar Coronal and Wind Models: Impact on Exoplanets
Authors: A. A. Vidotto (Trinity College Dublin)
Comments: Chapter published in the "Handbook of Exoplanets", Editors in Chief: Juan Antonio Belmonte and Hans Deeg, Section Editor: Nuccio Lanza. Springer Reference Works
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)

Surface magnetism is believed to be the main driver of coronal heating and stellar wind acceleration. Coronae are believed to be formed by plasma confined in closed magnetic coronal loops of the stars, with winds mainly originating in open magnetic field line regions. In this Chapter, we review some basic properties of stellar coronae and winds and present some existing models. In the last part of this Chapter, we discuss the effects of coronal winds on exoplanets.

[45]  arXiv:1709.07801 [pdf]
Title: Comparison of Helioseismic Far-side Active Region Detections with STEREO Far-Side EUV Observations of Solar Activity
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Seismic maps of the Sun's far hemisphere, computed from Doppler data from the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) are now being used routinely to detect strong magnetic regions on the far side of the Sun (http:/jsoc.stanford.edu/data/farside/). To test the reliability of this technique, the helioseismically inferred active region detections are compared with far-side observation of solar activity from the Solar TErrestrial RElations Observatory (STEREO), using brightness in extreme ultraviolet light (EUV) as a proxy for magnetic fields. Two approaches are used to analyze nine months of STEREO and HMI data. In the first approach, we determine whether or not new large east-limb active regions are detected seismically on the far side before they appear Earth side and study how the detectability of these regions relates to their EUV intensity. We find that, while there is a range of EUV intensities for which far-side regions may or may not be detected seismically, there appears to be an intensity level above which they are almost always detected and an intensity level below which they are never detected. In the second approach, we analyze concurrent extreme ultraviolet and helioseismic far-side observations. We find that 100% (22) of the far-side seismic regions correspond to an extreme ultraviolet plage; 95% of these either became a NOAA-designated magnetic region when reaching the east limb or were one before crossing to the far side. A low but significant correlation is found between the seismic signature strength and the EUV intensity of a farside region.

[46]  arXiv:1709.07803 [pdf, ps, other]
Title: Coulomb explosion of polycyclic aromatic hydrocarbons induced by heavy cosmic rays: carbon chains production rates
Comments: 21 pages, 19 figures and 4 tables
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Cosmic Rays (CR) process the matter of the Interstellar Medium. Such energetic processing not only modifies the interstellar matter but also injects chemical species in the gas phase. In this work, we study the effect of the CR on the astrophysical polycyclic aromatic hydrocarbons (PAH). For events in which many electrons are stripped out from the PAH by interaction with a heavy cosmic ray particle, coulomb explosion takes place and carbon chains are produced. The fragments production rates of carbon chains are of particular interest for astrophysical models. We computed PAH multi-ionization cross sections with an Independent Atom and Electron collisional model. We introduced and used a model to predict the fragmentation pattern for the coulomb explosion. Experimental measurements on small hydrocarbons, C$_{60}$ and PAHs were used to set confidence intervals on the calculations results.
The carbon chains production rates were calculated using different CR fluxes and elemental compositions, to account for the variations expected in various astrophysical environments. A range of PAH sizes and compactness were also explored. The PAH lifetime with respect to a standard interstellar CR flux (corresponding to an H$_2$ ionization rate of $\zeta \approx$ 6.10$^{-17}$s$^{-1}$) is found to be in the order of a few billion years. The production rates of interstellar carbon chains containing around 5-15 carbon atoms are in the order of few to many tens of percent of the H$_2$ ionization rate $\zeta$. The exact rate value relies on the nature of the PAH and on the CR composition. In diffuse medium, with ten percent of the available cosmic carbon locked in PAHs, this process leads to carbon chain fractional abundances at steady state, in the range of $10^{-15}$-$10^{-14}$, with a confidence interval of about one order of magnitude. It reaches $10^{-13}$ in quiescent dense clouds.

[47]  arXiv:1709.07818 [pdf, other]
Title: HR 7098: A new cool HgMn star?
Comments: 3 pages, 2 figures, conference proceeding SF2A 2017. arXiv admin note: substantial text overlap with arXiv:1609.04915
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Using one archival high dispersion high quality spectrum of HR 7098 (A0V) obtained with the \'echelle spectrograph SOPHIE at Observatoire de Haute Provence, we show that this star is not a superficially normal A0V star as hitherto thought. The model atmosphere and spectrum synthesis modeling of the spectrum of HR 7098 reveals real departures of its abundances from the solar composition. We report here on our first determinations of the elemental abundances of 35 elements in the atmosphere of HR 7098. Helium and Carbon are underabundant whereas the very heavy elements are overabundant in HR 7098.

[48]  arXiv:1709.07843 [html]
Title: VERITAS contributions to the 35th International Cosmic Ray Conference
Comments: html page. 2017 ICRC, Busan, South Korea. A full list of author affiliations can be found at this link: this https URL
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Compilation of papers presented by the VERITAS Collaboration at the 35th International Cosmic Ray Conference (ICRC), held July 12 through July 20, 2017 in Busan, South Korea.

[49]  arXiv:1709.07853 [pdf, other]
Title: Higgs inflation with loop corrections in the Palatini formulation
Comments: 31 pages, 22 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)

We compare Higgs inflation in the metric and Palatini formulations of general relativity, with loop corrections are treated in a simple approximation. We consider Higgs inflation on the plateau, at a critical point, at a hilltop and in a false vacuum. In the last case there are only minor differences. Otherwise we find that in the Palatini formulation the tensor-to-scalar ratio is consistently suppressed, spanning the range $1\times10^{-13}<r<7\times10^{-5}$, compared to the metric case result $2\times10^{-5}<r<0.2$. Even when the values of $n_s$ and $r$ overlap, the running and running of the running are different in the two formulations. Therefore, if Higgs is the inflaton, inflationary observables can be used to distinguish between different gravitational degrees of freedom, in this case to determine whether the connection is an independent variable. Non-detection of $r$ in foreseeable future observations would not rule out Higgs inflation, only its metric variant. We conclude that in order to fix the theory of Higgs inflation, not only the particle physics UV completion but also the gravitational degrees of freedom have to be explicated.

[50]  arXiv:1709.07854 [pdf, other]
Title: Relativistic asymmetries in the galaxy cross-correlation function
Comments: 10 pages, 10 figures, see link for a combined video summary of this and three other related papers posted today: this https URL . An elementary introduction to gravitational redshift is here: this https URL
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA); General Relativity and Quantum Cosmology (gr-qc); Popular Physics (physics.pop-ph)

We study the asymmetry in the two-point cross-correlation function of two populations of galaxies focusing in particular on the relativistic effects that include the gravitational redshift. We derive the cross-correlation function on small and large scales using two different approaches: General Relativistic and Newtonian perturbation theory. Following recent work by Bonvin et al., Gaztanaga et al. and Croft, we calculate the dipole and the shell estimator with the two procedures and we compare our results. We find that while General Relativistic Perturbation Theory (GRPT) is able to make predictions of relativistic effects on very large, obviously linear scales (r > 50 Mpc/h), the presence of non-linearities physically occurring on much smaller scales (down to those describing galactic potential wells) can strongly affect the asymmetry estimators. These can lead to cancellations of the relativistic terms, and sign changes in the estimators on scales up to r ~ 50 Mpc/h. On the other hand, with an appropriate non-linear gravitational potential, the results obtained using Newtonian theory can successfully describe the asymmetry on smaller, non-linear scales (r < 20 Mpc/h) where gravitational redshift is the dominant term. On larger scales the asymmetry is much smaller in magnitude, and measurement is not within reach of current observations. This is in agreement with the observational results obtained by Gaztnaga et al. and the first detection of relativistic effects (on (r < 20 Mpc/h) scales) by Alam et al.

[51]  arXiv:1709.07855 [pdf, other]
Title: Relativistic distortions in the large-scale clustering of SDSS-III BOSS CMASS galaxies
Comments: 13 pages, 10 figures, published in MNRAS, see link for a combined video summary of this and three other related papers posted today: this https URL . An elementary introduction to gravitational redshift is here: this https URL
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA); General Relativity and Quantum Cosmology (gr-qc); Popular Physics (physics.pop-ph)

General relativistic effects have long been predicted to subtly influence the observed large-scale structure of the universe. The current generation of galaxy redshift surveys have reached a size where detection of such effects is becoming feasible. In this paper, we report the first detection of the redshift asymmetry from the cross-correlation function of two galaxy populations which is consistent with relativistic effects. The dataset is taken from the Sloan Digital Sky Survey DR12 CMASS galaxy sample, and we detect the asymmetry at the $2.7\sigma$ level by applying a shell-averaged estimator to the cross-correlation function. Our measurement dominates at scales around $10$ h$^{-1}$Mpc, larger than those over which the gravitational redshift profile has been recently measured in galaxy clusters, but smaller than scales for which linear perturbation theory is likely to be accurate. The detection significance varies by 0.5$\sigma$ with the details of our measurement and tests for systematic effects. We have also devised two null tests to check for various survey systematics and show that both results are consistent with the null hypothesis. We measure the dipole moment of the cross-correlation function, and from this the asymmetry is also detected, at the $2.8 \sigma$ level. The amplitude and scale-dependence of the clustering asymmetries are approximately consistent with the expectations of General Relativity and a biased galaxy population, within large uncertainties. We explore theoretical predictions using numerical simulations in a companion paper.

[52]  arXiv:1709.07856 [pdf, other]
Title: Relativistic Effects on Galaxy Redshift Samples due to Target Selection
Comments: 11 pages, 8 figures, published in MNRAS, see link for a combined video summary of this and three other related papers posted today: this https URL . An elementary introduction to gravitational redshift is here: this https URL
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA); General Relativity and Quantum Cosmology (gr-qc); Popular Physics (physics.pop-ph)

In a galaxy redshift survey the objects to be targeted for spectra are selected from a photometrically observed sample. The observed magnitudes and colours of galaxies in this parent sample will be affected by their peculiar velocities, through relativistic Doppler and relativistic beaming effects. In this paper we compute the resulting expected changes in galaxy photometry. The magnitudes of the relativistic effects are a function of redshift, stellar mass, galaxy velocity and velocity direction. We focus on the CMASS sample from the Sloan Digital Sky Survey (SDSS), Baryon Oscillation Spectroscopic Survey (BOSS), which is selected on the basis of colour and magnitude. We find that 0.10\% of the sample ($\sim 585$ galaxies) has been scattered into the targeted region of colour-magnitude space by relativistic effects, and conversely 0.09\% of the sample ($\sim 532$ galaxies) has been scattered out. Observational consequences of these effects include an asymmetry in clustering statistics, which we explore in a companion paper. Here we compute a set of weights which can be used to remove the effect of modulations introduced into the density field inferred from a galaxy sample. We conclude by investigating the possible effects of these relativistic modulation on large scale clustering of the galaxy sample.

[53]  arXiv:1709.07859 [pdf, other]
Title: N-body simulations of gravitational redshifts and other relativistic distortions of galaxy clustering
Comments: 13 pages, 10 figures, published in MNRAS, see link for a combined video summary of this and three other related papers posted today: this https URL An elementary introduction to gravitational redshift is here: this https URL
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA); General Relativity and Quantum Cosmology (gr-qc); Popular Physics (physics.pop-ph)

Large redshift surveys of galaxies and clusters are providing the first opportunities to search for distortions in the observed pattern of large-scale structure due to such effects as gravitational redshift. We focus on non-linear scales and apply a quasi-Newtonian approach using N-body simulations to predict the small asymmetries in the cross-correlation function of two galaxy different populations. Following recent work by Bonvin et al., Zhao and Peacock and Kaiser on galaxy clusters, we include effects which enter at the same order as gravitational redshift: the transverse Doppler effect, light-cone effects, relativistic beaming, luminosity distance perturbation and wide-angle effects. We find that all these effects cause asymmetries in the cross-correlation functions. Quantifying these asymmetries, we find that the total effect is dominated by the gravitational redshift and luminosity distance perturbation at small and large scales, respectively. By adding additional subresolution modelling of galaxy structure to the large-scale structure information, we find that the signal is significantly increased, indicating that structure on the smallest scales is important and should be included. We report on comparison of our simulation results with measurements from the SDSS/BOSS galaxy redshift survey in a companion paper.

[54]  arXiv:1709.07863 [pdf, other]
Title: Molecular abundances and C/O ratios in chemically evolving planet-forming disk midplanes
Comments: Accepted by A&A. 18
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

(Abridged) Exoplanet atmospheres are thought be built up from accretion of gas as well as pebbles and planetesimals in the midplanes of planet-forming disks. The chemical composition of this material is usually assumed to be unchanged during the disk lifetime. However, chemistry can alter the relative abundances of molecules in this planet-building material. To assess the impact of disk chemistry during the era of planet formation, an extensive kinetic chemistry gas-grain reaction network is utilised to evolve the abundances of chemical species over time. Given a high level of ionisation, chemical evolution in protoplanetary disk midplanes becomes significant after a few times $10^{5}$ yrs, and is still ongoing by 7 Myr between the H$_{2}$O and the O$_{2}$ icelines. Importantly, the changes in the abundances of the major elemental carbon and oxygen-bearing molecules imply that the traditional "stepfunction" for the C/O ratios in gas and ice in the disk midplane (as defined by sharp changes at icelines of H$_{2}$O, CO$_{2}$ and CO) evolves over time, and cannot be assumed fixed. In addition, at lower temperatures (< 29 K), gaseous CO colliding with the grains gets converted into CO$_{2}$ and other more complex ices, lowering the CO gas abundance between the O$_{2}$ and CO thermal icelines. This effect can mimic a CO iceline at a higher temperature than suggested by its binding energy. Chemistry in the disk midplane is ionisation-driven, and evolves over time. In order to reliably predict the atmospheric compositions of forming planets, as well as to relate observed atmospheric C/O ratios of exoplanets to where and how the atmospheres have formed in a disk midplane, chemical evolution needs to be considered and implemented into planet formation models.

[55]  arXiv:1709.07865 [pdf, other]
Title: $\mathcal O(10) M_\odot$ primordial black holes and string axion dark matter
Comments: 12 pages, 8 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

LIGO-Virgo collaboration has found black holes as heavy as $M \sim 30M_\odot$ through the detections of the gravitational waves emitted during their mergers. Primordial black holes (PBHs) produced by inflation could be an origin of such events. While it is tempting to presume that these PBHs constitute all Dark Matter (DM), there exists a number of constraints for PBHs with $\mathcal{O} (10) M_\odot$ which contradict with the idea of PBHs as all DM. Also, it is known that weakly interacting massive particle (WIMP) that is a common DM candidate is almost impossible to coexist with PBHs. These observations motivate us to pursue another candidate of DM. In this paper, we assume that the string axion solving the strong CP problem makes up all DM, and discuss the coexistence of string axion DM and inflationary PBHs for LIGO events.