We gratefully acknowledge support from
the Simons Foundation and Leiden University.

Astrophysics

New submissions

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New submissions for Thu, 23 Jan 20

[1]  arXiv:2001.07718 [pdf, other]
Title: Second order Fermi reacceleration mechanisms and large scale synchrotron radio emission in intra-cluster bridges
Authors: G. Brunetti, F. Vazza
Comments: 5 pages, 3 figures (+ Supplementary Material). Physical Review Letters, in press
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Radio observations at low frequencies with the Low Frequency Array (LOFAR) start discovering gigantic radio bridges connecting pairs of massive galaxy clusters. These observations probe unexplored mechanisms of in situ particle acceleration that operate on volumes of several Mpc$^3$. Numerical simulations suggest that such bridges are dynamically complex and that weak shocks and super-Alfv\'{e}nic turbulence can be driven across the entire volume of these regions. In this Letter we explore, for the first time, the role of second order Fermi mechanisms for the reacceleration of relativistic electrons interacting with turbulence in these peculiar regions. We assume the turbulent energy flux measured in simulations and adopt a scenario in which relativistic particles scatter with magnetic field lines diffusing in super-Alfv\'enic turbulence and magnetic fields are amplified by the same turbulence. We show that steep spectrum and volume filling synchrotron emission can be generated in the entire intra-cluster bridge region thus providing a natural explanation for radio bridges. Consequently, radio observations have the potential to probe the dissipation of energy on scales larger than galaxy clusters and second order Fermi mechanisms operating in physical regimes that are still poorly explored. This has a potential impact on several branches of astrophysics and cosmology.

[2]  arXiv:2001.07719 [pdf, other]
Title: A versatile tool for cluster lensing source reconstruction. I. methodology and illustration on sources in the Hubble Frontier Field Cluster MACS J0717.5+3745
Comments: Submitted to MNRAS, 16 pages, 11 figures, 6 tables
Subjects: Astrophysics of Galaxies (astro-ph.GA); Instrumentation and Methods for Astrophysics (astro-ph.IM)

We describe a general purpose method to reconstruct the intrinsic properties of sources lensed by the gravitational potential of foreground clusters of galaxies. The tool Lenstruction is implemented in the publicly available multi-purpose gravitational lensing software Lenstronomy, in order to provide easy and fast solution to this common astrophysical problem. The tool is based on forward modeling the appearance of the source in the image plane, taking into account the distortion by lensing and the instrumental point spread function (PSF). For singly-imaged sources a global lens model in the format of the Hubble Frontier Fields (HFF) lensing maps is required as a starting point. For multiply-imaged sources, the tool can also fit and apply first (deflection) second (shear, convergence) and third order (flexion) corrections to the local gravitational potential to improve the overall reconstruction, depending on the quality of the data. We illustrate the performance and features of the code with two examples of multiply-imaged systems taken from the Hubble Frontier Fields, starting from five different publicly available cluster models. We find that, after our correction, the relative magnification - and other lensing properties - between the multiple images become robustly constrained. Furthermore, we find that scatter between models of the reconstructed source size and magnitude is reduced. The code and jupyter notebooks are publicly available.

[3]  arXiv:2001.07720 [pdf, other]
Title: Nine localised deviations from Keplerian rotation in the DSHARP circumstellar disks: Kinematic evidence for protoplanets carving the gaps
Comments: Accepted for publication in ApJ letters, 10 pages, 3 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA)

We present evidence for localised deviations from Keplerian rotation, i.e., velocity "kinks", in 8 of 18 circumstellar disks observed by the DSHARP program: DoAr 25, Elias 2-27, GW Lup, HD 143006, HD 163296, IM Lup, Sz 129 and WaOph 6. Most of the kinks are detected over a small range in both radial extent and velocity, suggesting a planetary origin, but for some of them foreground contamination prevents us from measuring their spatial and velocity extent. Because of the DSHARP limited spectral resolution and signal-to-noise in the 12CO J=2-1 line, as well as cloud contamination, the kinks are usually detected in only one spectral channel, and will require confirmation. The strongest circumstantial evidence for protoplanets in the absence of higher spectral resolution data and additional tracers is that, upon deprojection, we find that all of the candidate planets lie within a gap and/or at the end of a spiral detected in dust continuum emission. This suggests that a significant fraction of the dust gaps and spirals observed by ALMA in disks are caused by embedded protoplanets.

[4]  arXiv:2001.07721 [pdf, ps, other]
Title: Turbulence in a self-gravitating molecular cloud core
Comments: 8 pages, 5 figures, accepted for publication in ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA); Fluid Dynamics (physics.flu-dyn)

Externally driven interstellar turbulence plays an important role in shaping the density structure in molecular clouds. Here we study the dynamical role of internally driven turbulence in a self-gravitating molecular cloud core. Depending on the initial conditions and evolutionary stages, we find that a self-gravitating core in the presence of gravity-driven turbulence can undergo constant, decelerated, and accelerated infall, and thus has various radial velocity profiles. In the gravity-dominated central region, a higher level of turbulence results in a lower infall velocity, a higher density, and a lower mass accretion rate. As an important implication of this study, efficient reconnection diffusion of magnetic fields against the gravitational drag naturally occurs due to the gravity-driven turbulence, without invoking externally driven turbulence.

[5]  arXiv:2001.07725 [pdf, other]
Title: A stellar census in globular clusters with MUSE -- Extending the CaT-metallicity relation below the horizontal branch and applying it to multiple populations
Comments: 28 pages, 29 figures, 7 tables, accepted for publication in A&A
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

Aims. We use the spectra of more than 30,000 red giant branch (RGB) stars in 25 globular clusters (GC), obtained within the MUSE survey of Galactic globular clusters, to calibrate the Ca II triplet (CaT) metallicity relation and derive metallicities for all individual stars. We investigate the overall metallicity distributions as well as those of the different populations within each cluster.
Methods. The Ca II triplet in the near-infrared at 8498, 8542, and 8662 AA is visible in stars with spectral types between F and M and can be used to determine their metallicities. In this work, we calibrate the relation using average cluster metallicities from literature and MUSE spectra, and extend it below the horizontal branch - a cutoff that has traditionally been made to avoid a non-linear relation - using a quadratic function. In addition to the classic relation based on V-VHB we also present calibrations based on absolute magnitude and luminosity. The obtained relations are then used to calculate metallicities for all the stars in the sample and to derive metallicity distributions for different populations within a cluster, which have been separated using so-called "chromosome maps" based on HST photometry.
Results. We show that, despite the relatively low spectral resolution of MUSE (R=1900-3700) we can derive single star metallicities with a mean statistical intra-cluster uncertainty of ~0.12 dex. We present metallicity distributions for the RGB stars in 25 GCs, and investigate the different metallicities of the populations P3 (and higher) in so-called metal-complex or Type II clusters, finding metallicity variations in all of them. We also detected unexpected metallicity variations in the Type I cluster NGC 2808 and confirm the Type II status of NGC 7078.

[6]  arXiv:2001.07727 [pdf, other]
Title: Measurement of the B-band Galaxy Luminosity Function with Approximate Bayesian Computation
Comments: Submitted to JCAP, 42 pages, 20 figures, 4 appendices
Subjects: Astrophysics of Galaxies (astro-ph.GA)

The galaxy Luminosity Function (LF) is a key observable for galaxy formation, evolution studies and for cosmology. In this work, we propose a novel technique to forward model wide-field galaxy surveys using the fast image simulator UFig and measure the LF of galaxies in the B-band. We use Approximate Bayesian Computation (ABC) to constrain the galaxy population model parameters of the simulations and match data from the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). We define a number of distance metrics between the simulated and the survey data. By exploring the parameter space of the galaxy population model through ABC to find the set of parameters that minimize these distance metrics, we obtain constraints on the LFs of blue and red galaxies as a function of redshift. We find that $\mathrm{M^*}$ fades by $\Delta \mathrm{M}^*_{\mathrm{0.1-1.0,b}} = 0.37 \pm 0.34$ and $\Delta \mathrm{M}^*_{\mathrm{0.1-1.0,r}} = 0.58 \pm 0.42$ magnitudes between redshift $\mathrm{z = 1}$ and $\mathrm{z = 0.1}$ for blue and red galaxies, respectively. We also find that $\phi^*$ for blue galaxies stays roughly constant between redshift $\mathrm{z = 0.1}$ and $\mathrm{z=1}$, while for red galaxies it decreases of $\sim 90\%$. We compare our results to other measurements, finding good agreement at all redshifts, for both blue and red galaxies. To further test our results, we compare the redshift distributions for survey and simulated data. We use the spectroscopic redshift distribution from the VIMOS Public Extragalactic Redshift Survey (VIPERS) and we apply the same selection in colours and magnitudes on our simulations. We find a good agreement between the survey and the simulated redshift distributions. We provide best-fit values and uncertainties for the parameters of the LF. This work offers excellent prospects for measuring other galaxy population properties as a function of redshift using ABC.

[7]  arXiv:2001.07729 [pdf, other]
Title: Study of the variable broadband emission of Markarian 501 during the most extreme Swift X-ray activity
Comments: Accepted for publication in A&A. Corresponding authors: J. Becerra Gonz\'alez (jbecerra@iac.es), D. Paneque (dpaneque@mppmu.mpg.de), C. Wendel (cwendel@astro.uni-wuerzburg.de)
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Mrk501 is a very high-energy (VHE) gamma-ray blazar located at z=0.034. During a period of two weeks in July 2014, the highest X-ray activity of Mrk501 was observed in ~14 years of operation of the Neil Gehrels Swift Gamma-ray Burst Observatory. We characterize the broadband variability of Mrk501 from radio to VHE gamma rays, and evaluate whether it can be interpreted within theoretical scenarios widely used to explain the broadband emission from blazars. The temporal evolution of the most prominent and variable segments of the SED is described with a one-zone synchrotron self-Compton model with variations in the break energy of the electron energy distribution (EED), and with some adjustments in the magnetic field strength and spectral shape of the EED. A narrow feature at ~3 TeV was observed in the VHE spectrum measured on 2014 July 19 (MJD 56857.98), which is the day with the highest X-ray flux ($>0.3$ keV) measured during the entire Swift mission. This feature is inconsistent with the classical analytic functions to describe the measured VHE spectra (power law, log-parabola, and log-parabola with exponential cutoff) at more than 3$\sigma$. A fit with a log-parabola plus a narrow component is preferred over the fit with a single log-parabola at more than 4$\sigma$, and a dedicated Monte Carlo simulation estimated the significance of this extra component to be larger than 3$\sigma$. Under the assumption that this VHE spectral feature is real, we show that it can be reproduced with three distinct theoretical scenarios: a) a pileup in the EED due to stochastic acceleration; b) a structured jet with two-SSC emitting regions, with one region dominated by an extremely narrow EED; and c) an emission from an IC pair cascade.

[8]  arXiv:2001.07730 [pdf, other]
Title: The Clustering of X-ray Luminous Quasars
Comments: Accepted for publication in ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA)

The clustering of AGN sheds light on their typical large (Mpc-scale) environments, which can constrain the growth and evolution of supermassive black holes. Here we measure the clustering of luminous X-ray-selected AGN in the Stripe 82X and XMM-XXL-North surveys around the peak epoch of black hole growth, in order to investigate the dependence of luminosity on large-scale AGN environment. We compute the auto-correlation function of AGN in two luminosity bins, $10^{43}\leq L_X<10^{44.5}$ erg s$^{-1}$ at $z\sim 0.8$ and $L_X\geq 10^{44.5}$ erg s$^{-1}$ at $z\sim 1.8$, and calculate the AGN bias taking into account the redshift distribution of the sources using three different methods. Our results show that while the less luminous sample has an inferred typical halo mass that is smaller than for the more luminous AGN, the host halo mass may be less dependent on luminosity than suggested in previous work. Focusing on the luminous sample, we calculate a typical host halo mass of $\sim 10^{13}$ M$_{\odot}~h^{-1}$, which is similar to previous measurements of moderate-luminosity X-ray AGN and significantly larger than the values found for optical quasars of similar luminosities and redshifts. We suggest that the clustering differences between different AGN selection techniques are dominated by selection biases, and not due to a dependence on AGN luminosity. We discuss the limitations of inferring AGN triggering mechanisms from halo masses derived by large-scale bias.

[9]  arXiv:2001.07733 [pdf, other]
Title: Laminar Flame Speeds in Degenerate Oxygen-Neon Mixtures
Comments: 12 pages, 12 figures; Accepted to ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR)

The collapse of degenerate oxygen-neon cores (i.e., electron-capture supernovae or accretion-induced collapse) proceeds through a phase in which a deflagration wave ("flame") forms at or near the center and propagates through the star. In models, the assumed speed of this flame influences whether this process leads to an explosion or to the formation of a neutron star. We calculate the laminar flame speeds in degenerate oxygen-neon mixtures with compositions motivated by detailed stellar evolution models. These mixtures include trace amounts of carbon and have a lower electron fraction than those considered in previous work. We find that trace carbon has little effect on the flame speeds, but that material with electron fraction $Y_e \approx 0.48-0.49$ has laminar flame speeds that are $\approx 2$ times faster than those at $Y_e = 0.5$. We provide tabulated flame speeds and a corresponding fitting function so that the impact of this difference can be assessed via full star hydrodynamical simulations of the collapse process.

[10]  arXiv:2001.07736 [pdf, other]
Title: Figuring Out Gas & Galaxies in Enzo (FOGGIE). III. The Mocky Way: Investigating Biases in Observing the Milky Way's Circumgalactic Medium
Comments: Submitted to ApJ. Comments are welcome
Subjects: Astrophysics of Galaxies (astro-ph.GA)

The circumgalactic medium (CGM) of the Milky Way is mostly obscured by nearby gas in position-velocity space due to the location and motion of observers inside the Galaxy. While most studies on the Milky Way's CGM to date focus on easier-to-detect high-velocity gas ($|v_{\rm LSR}|\gtrsim100$ km s$^{-1}$), it only partially represents the entire CGM, resulting in substantial biases. Here we investigate four observational biases inherent in the studies of the Milky Way's CGM with mock observations on a Milky-Way analog from the FOGGIE simulations. With a mock observer placed inside the simulated galaxy at off-center locations consistent with that of the Sun, we find that: (i) high-velocity-based studies could miss $\sim$2/3 of the Milky Way's CGM mass; (ii) once we correct velocities from the local standard of rest to the galaxy's rest frame, gas infall rate ($\dot{M}$) for cold gas observable in HI 21cm emission is reduced from -0.25 M$_\odot$ to -0.05 M$_\odot$, while $\dot{M}$ for gases at warmer phases are less affected; (iii) OVI and NV are likely to be good UV tracers of the Milky Way's outer CGM ($r\gtrsim$15 kpc), whereas CIV maybe less sensitive; (iv) because of the clumpiness and radial distribution of CGM gas, the scatter in ionic column densities is a factor of 2 higher when the CGM is observed from the inside-out versus from external views. Our work highlights that observations of the Milky Way's CGM, especially those using HI emission and UV absorption lines, are highly biased because we reside inside the Galaxy. We demonstrate that these biases can be quantified and calibrated through synthetic observations with simulated Milky-Way analogs.

[11]  arXiv:2001.07737 [pdf, other]
Title: The $Gaia$-$Kepler$ Stellar Properties Catalog I: Homogeneous Fundamental Properties for 186,000 $Kepler$ Stars
Comments: 21 pages, 12 figures, 2 tables. Submitted to AAS Journals. Electronic versions of the tables will be made available following a favorable review
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA)

An accurate and precise $Kepler$ Stellar Properties Catalog is essential for the interpretation of the $Kepler$ exoplanet survey results. Previous $Kepler$ Stellar Properties Catalogs have focused on reporting the best-available parameters for each star, but this has required combining data from a variety of heterogeneous sources. We present the $Gaia$-$Kepler$ Stellar Properties Catalog, a set of stellar properties of 186,301 $Kepler$ stars, homogeneously derived from isochrones and broadband photometry, $Gaia$ Data Release 2 parallaxes, and spectroscopic metallicities, where available. Our photometric effective temperatures, derived from $g-K_s$ colors, are calibrated on stars with interferometric angular diameters. Median catalog uncertainties are 112 K for $T_{\mathrm{eff}}$, 0.05 dex for $\log g$, 4% for $R_\star$, 7% for $M_\star$, 13% for $\rho_\star$, 10% for $L_\star$, and 56% for stellar age. These precise constraints on stellar properties for this sample of stars will allow unprecedented investigations into trends in stellar and exoplanet properties as a function of stellar mass and age. In addition, our homogeneous parameter determinations will permit more accurate calculations of planet occurrence and trends with stellar properties.

[12]  arXiv:2001.07738 [pdf, other]
Title: Exploring Early and Late Cosmology with Next Generation Surveys
Comments: 18 pages, 12 figures, 2 tables
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Perturbations from inflation evolve into large scale structure of the late universe, and encode abundant cosmic structure formation physics. We allow freedom in the primordial power spectrum, rather than assuming a power law scale dependence, to study its impact on cosmological parameter determination. Combining various generations of cosmic microwave background (CMB) data and galaxy redshift survey data, we investigate the constraints on reconstruction of the primordial curvature perturbation power spectrum and the late time cosmology, especially the sum of neutrino masses. We quantify how each successive generation, in CMB and galaxy surveys, provides significant improvements, often by factors of several. By using CMB polarization information over a broad range of angular scales, and galaxy redshift data in many bins of redshift, one can allow inflationary freedom and still constrain parameters comparably to assuming power law dependence. The primordial power spectrum can be reconstructed at the subpercent level in a dozen wavenumber bins, while simultaneously fitting the sum of neutrino masses to 14 meV.

[13]  arXiv:2001.07742 [pdf, other]
Title: The orbital phase space of contracted dark matter halos
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We study the orbital phase-space of dark matter (DM) halos in the AURIGA suite of cosmological hydrodynamics simulations of Milky Way analogues. We characterise halos by their spherical action distribution, a function of the specific angular momentum, and the radial action, of the DM particles. By comparing DM-only and hydrodynamical simulations of the same halos, we investigate the contraction of DM halos caused by the accumulation of baryons at the centre. We find a small systematic suppression of the radial action in the DM halos of the hydrodynamical simulations, suggesting that the commonly used adiabatic contraction approximation can result in an underestimate of the density by ~ 8%. We apply an iterative algorithm to contract the AURIGA DM halos given a baryon density profile and halo mass, recovering the true contracted DM profiles with an accuracy of ~15%, that reflects halo-to-halo variation. Using this algorithm, we infer the total mass profile of the Milky Way's contracted DM halo. We derive updated values for the key astrophysical inputs to DM direct detection experiments: the DM density and velocity distribution in the Solar neighbourhood.

[14]  arXiv:2001.07785 [pdf, other]
Title: Galactic ionising photon budget during the Epoch ofReionisation in the Cosmic Dawn II simulation
Comments: Submitted to MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Cosmic Dawn ("CoDa") II yields the first statistically-meaningful determination of the relative contribution to reionization by galaxies of different halo mass, from a fully-coupled radiation-hydrodynamics simulation of the epoch of reionization large enough ($\sim 100$ Mpc) to model global reionization while resolving the formation of all galactic halos above $\sim 10^8 \msol$. Cell transmission inside high-mass haloes is bi-modal -- ionized cells are transparent, while neutral cells absorb the photons their stars produce - and the halo escape fraction $ \fesc$ reflects the balance of star formation rate ("SFR") between these modes. The latter is increasingly prevalent at higher halo mass, driving down $\fesc$ (we provide analytical fits to our results), whereas halo escape luminosity, proportional to $\fesc \times {\rm SFR}$, increases with mass. Haloes with dark matter masses within $6\cdot 10^{8} \msol < \mh < 3\cdot 10^{10} \msol$ produce $\sim 80$% of the escaping photons at z=7, when the Universe is 50% ionized, making them the main drivers of cosmic reionization. Less massive haloes, though more numerous, have low SFRs and contribute less than 10% of the photon budget then, despite their high $\fesc$. High mass haloes are too few and too opaque, contributing $<10$% despite their high SFRs. The dominant mass range is lower (higher) at higher (lower) redshift, as mass function and reionization advance together (e.g. at z$=8.5$, x$_{\rm HI}=0.9$, $\mh < 5.10^9 \msol$ haloes contributed $\sim 80$%). Galaxies with UV magnitudes $M_{AB1600}$ between $-12$ and $-19$ dominated reionization between z$=6$ and 8.

[15]  arXiv:2001.07802 [pdf, other]
Title: SZ Scaling Relations of Galaxy Groups and Clusters Near the North Ecliptic Pole
Comments: 15 pages, 5 figures, 4 tables, Accepted for publication in the Astrophysical Journal
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

SZ scaling relations have been used to test the self-similar prediction for massive galaxy clusters, but little attention has been given to individual galaxy groups. We investigate the scaling relations of galaxy groups and clusters near the North Ecliptic Pole using X-ray and SZ observations. This region of the sky is where both the ROSAT and Planck satellites achieved their deepest observations, permitting the investigation of lower mass systems. Our sample consists of 62 X-ray detected groups and clusters, spanning a mass range of $10^{13.4}M_{\odot}<~M_{500}<10^{15}M_{\odot}$ and redshifts of $0.03\lesssim z \lesssim 0.82$. We extract the total SZ flux from unresolved Planck data and estimate the fraction of the SZ flux within $R_{500}$ assuming two different pressure profiles. The SZ scaling relations were derived using a Bayesian technique that accounts for censored data. We find a power law slope of $1.73^{+0.19}_{-0.18}$ for the $Y_{SZ}-M_{500}$ relation which is consistent with the self-similar prediction of 5/3. The slope of $0.89^{+0.09}_{-0.08}$ for the $Y_{SZ}-L_{X,500}$ relation is in agreement with other observational studies but not the self-similar prediction of 5/4, and the $Y_{SZ}-Y_{X}$ relation lies below the 1:1 relation when the slope is fixed to unity. The determined scaling relations are dependent on the selected pressure profile, so resolved data are needed to determine the effects of AGN feedback. In addition, we find a number of potential cluster candidates in the Planck Compton maps that were not identified in our X-ray sample.

[16]  arXiv:2001.07807 [pdf, other]
Title: Accretion-Driven Sources in Spatially Resolved Ly$α$ Emitters
Authors: B. Dittenber (1), M. S. Oey (1), E. Hodges-Kluck (2,3), E. Gallo (1), M. Hayes (4), G. Oestlin (4), J. Melinder (4)
Comments: 10 pages, 3 figures, 2 tables. Submitted to ApJ Letters
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Ly$\alpha$ emission is a standard tracer of starburst galaxies at high redshift. However, a number of local Ly$\alpha$ emitters (LAEs) are X-ray sources, suggesting a possible origin of Ly$\alpha$ photons other than young, hot stars, and which may be active at much later ages relative to the parent starburst. Resolved, nearby LAEs offer the opportunity to discriminate between diffuse X-ray emission arising from supernova-heated gas, high-mass X-ray binaries (HMXBs), or low-luminosity active galactic nuclei (LLAGN). We examine archival X-ray imaging from Chandra and XMM-Newton for 11 galaxies with spatially resolved Ly$\alpha$ imaging to determine the luminosity, morphology, and spectral hardness of the X-ray sources. The data are consistent with 9 of the 12, bright Ly$\alpha$ sources being driven by luminous, $10^{40}$ erg s$^{-1}$ X-ray sources. Half of the 8 Chandra sources are unresolved. The data suggest that nuclear activity, whether from LLAGN or nuclear starbursts, may play an important role in Ly$\alpha$ emission. Our results also suggest a significant link between Ly$\alpha$ emission and HMXBs, ULXs, and/or LLAGN, which would imply that Ly$\alpha$ may be generated over timescales 1 - 2 orders of magnitude longer than produced by photoionization from OB stars. This highlights a critical need to quantify the relative contributions of different sources across cosmic time, to interpret Ly$\alpha$ observations and the resulting properties of distant galaxies.

[17]  arXiv:2001.07848 [pdf, other]
Title: Small Aperture Telescopes for the Simons Observatory
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

The Simons Observatory (SO) is an upcoming cosmic microwave background (CMB) experiment located on Cerro Toco, Chile, that will map the microwave sky in temperature and polarization in six frequency bands spanning 27 to 285 GHz. SO will consist of one 6-meter Large Aperture Telescope (LAT) fielding $\sim$30,000 detectors and an array of three 0.42-meter Small Aperture Telescopes (SATs) fielding an additional 30,000 detectors. This synergy will allow for the extremely sensitive characterization of the CMB over angular scales ranging from an arcmin to tens of degrees, enabling a wide range of scientific output. Here we focus on the SATs targeting degree angular scales with successive dichroic instruments observing at Mid-Frequency (MF: 93/145 GHz), Ultra-High-Frequency (UHF: 225/285 GHz), and Low-Frequency (LF: 27/39 GHz). The three SATs will be able to map $\sim$10\% of the sky to a noise level of $\mu$K-arcmin when combining 93 and 145 GHz. The multiple frequency bands will allow the CMB to be separated from galactic foregrounds (primarily synchrotron and dust), with the primary science goal of characterizing the primordial tensor-to-scalar ratio, $r$, at a target level of $\sigma \left(r\right) \approx 0.003$.

[18]  arXiv:2001.07879 [pdf, other]
Title: Efficiently jet-powered radiation in intermediate-luminosity optical transients (ILOTS)
Authors: Noam Soker (Technion, Israel)
Comments: Will be submitted in two days to allow comments by readers
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

I show that a flow structure where wide jets hit a slower expanding shell might be very efficient in channelling the kinetic energy of the jets to radiation, therefore accounting for, at a least a fraction of, intermediate luminosity optical transients (ILOTs) where the total radiation energy is much larger than what recombination energy of the outflow can supply. This type of flow might occur in the frame of the high-accretion-powered ILOT (HAPI) model, where there is a high mass accretion rate as a result of stellar merger or mass transfer in a binary system. I derive the condition on the jets half-opening angle for the jets not to penetrate through the slow shell, as well as the ratio of the photon diffusion time to expansion time. This ratio cannot be too large if a large fraction of the thermal energy is channelled to radiation. I apply the jet-powered radiation model to the Great Eruption of Eta Carinae and to V838Mon, and find a plausible set of parameters for both ILOTs. I expect the jet-powered radiation model to be more efficient in converting kinetic energy to radiation than ILOT models that are based on equatorial mass concentration. In many cases, thought, I expect both jets and equatorial mass concentration to occur in the same system.

[19]  arXiv:2001.07882 [pdf, other]
Title: Is GW190425 consistent with being a neutron star$-$black hole merger?
Comments: 6 pages, 3 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc)

GW190425 is the second neutron star merger event detected by the Advanced LIGO/Virgo detectors. If interpreted as a double neutron star merger, the total gravitational mass is substantially larger than that of the binary systems identified in the Galaxy. In this work we analyze the gravitational wave data within the neutron star$-$black hole merger scenario. For the black hole, we yield a mass of $2.34^{+0.38}_{-0.27}M_\odot$ and an aligned spin of $0.133^{+0.070}_{-0.054}$. As for the neutron star we find a mass of $1.18^{+0.13}_{-0.14}M_\odot$ and the dimensionless tidal deformability of $1.7^{+5.5}_{-1.4}\times 10^{3}$. The ranges of these parameters are corresponding to the 90\% credible intervals. The inferred masses of the neutron star and the black hole are not in tension with current observations and we suggest that GW190425 is a viable candidate of a neutron star$-$black hole merger event. Benefited from the continual enhancement of the sensitivity of the advanced gravitational detectors and the increase of the number of the detectors, similar events are anticipated to be much more precisely measured and the presence of black holes below the so-called mass gap will be unambiguously clarified. If confirmed, the mergers of neutron stars with (quickly rotating) low-mass black holes are likely important production sites of the heaviest $r-$process elements.

[20]  arXiv:2001.07891 [pdf, other]
Title: Probing compact dark matter with gravitational wave fringes detected by the Einstein Telescope
Comments: 5 pages, 3 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)

Unlike the electromagnetic radiation from astrophysical objects, gravitational waves (GWs) from binary star mergers have much longer wavelengths and are inherently consistent. For ground-based GW detectors, when the lens object between the source and the earth has mass $\sim 1-10^5M_\odot$, the diffraction effect should be considered since the chirping wavelengths are comparable to the scale of the barrier (its Schwarzschild radius). The waveform will thus be distorted as the fringes. In this work, we show that signals from the third-generation GW detectors like the Einstein Telescope (ET) would be a smoking gun for probing the nature of compact dark matter (CDM) or primordial black holes. The constraint of the mass can be up to the level of $M_{\rm{CDM}}\sim 5M_\odot$. For a null search of the fringes, one-year observation of ET can constrain the CDM density fraction to $\sim10^{-2}-10^{-5}$ in the mass range $M_{\rm{CDM}}=10M_\odot-100M_\odot$.

[21]  arXiv:2001.07927 [pdf, ps, other]
Title: Stellar Properties of the Host Galaxy of an Ultraluminous X-ray Source in NGC 5252
Comments: To appear in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

An ultraluminous X-ray source (ULX) in NGC 5252 has been known as a strong candidate for an off-nuclear intermediate-mass black hole. We present near-infrared imaging data of the ULX obtained with the William Herschel Telescope. Using this data we estimate a stellar mass associated with the ULX of $\approx 10^{7.9\pm0.1}M_{\rm \odot}$ , suggesting that it could be (the remnant of) a dwarf galaxy that is in the process of merging with NGC 5252. Based on a correlation between the mass of the central black hole (BH) and host galaxy, the ULX is powered by a $10^5M_{\rm \odot}$ black hole. Alternatively, if the BH mass is $\approx 10^6M_{\rm \odot}$ or larger, the host galaxy of the ULX must have been heavily stripped during the merger. The ULX $K_s$-band luminosity is two orders of magnitude smaller than that expected from an ordinary active galactic nucleus with the observed [O III] luminosity, which also suggests the ULX lacks a dusty torus. We discuss how these findings provide suggestive evidence that the ULX is hosting an intermediate-mass black hole.

[22]  arXiv:2001.07968 [pdf, other]
Title: GRAMSES: a new route to general relativistic $N$-body simulations in cosmology. Part II. Initial conditions
Comments: 27 pages, 4 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)

We address the generation of initial conditions (ICs) for GRAMSES, a code for nonlinear general relativistic (GR) $N$-body cosmological simulations recently introduced in Ref. [1]. GRAMSES adopts a constant mean curvature slicing with a minimal distortion gauge, where the linear growth rate is scale-dependent, and the standard method for realising initial particle data is not straightforwardly applicable. A new method is introduced, in which the initial positions of particles are generated from the displacement field realised for a matter power spectrum as usual, but the velocity is calculated by finite-differencing the displacement fields around the initial redshift. In this way, all the information required for setting up the initial conditions is drawn from three consecutive input matter power spectra, and additional assumptions such as scale-independence of the linear growth factor and growth rate are not needed. We implement this method in a modified 2LPTic code, and demonstrate that in a Newtonian setting it can reproduce the velocity field given by the default 2LPTic code with subpercent accuracy. We also show that the matter and velocity power spectra of the initial particle data generated for GRAMSES simulations using this method agree very well with the linear-theory predictions in the particular gauge used by GRAMSES. Finally, we discuss corrections to the finite difference calculation of the velocity when radiation is present, as well as additional corrections implemented in GRAMSES to ensure consistency. This method can be applied in ICs generation for GR simulations in generic gauges, and simulations of cosmological models with scale-dependent linear growth rate.

[23]  arXiv:2001.07975 [pdf, other]
Title: Improving transit characterisation with Gaussian process modelling of stellar variability
Comments: 13 pages, 5 figures, 11 tables accepted for publication in A&A
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM); Solar and Stellar Astrophysics (astro-ph.SR)

New photometric space missions to detect and characterise transiting exoplanets are focusing on bright stars to obtain high cadence, high signal-to-noise light curves. Since these missions will be sensitive to stellar oscillations and granulation even for dwarf stars, they will be limited by stellar variability. We tested the performance of Gaussian process (GP) regression on the characterisation of transiting planets, and in particular to determine how many components of variability are necessary to describe high cadence, high signal-to-noise light curves expected from CHEOPS and PLATO. We found that the best GP stellar variability model contains four to five variability components: one stellar oscillation component, two to four granulation components, and/or one rotational modulation component. This high number of components is in contrast with the one-component GP model (1GP) commonly used in the literature for transit characterisation. Therefore, we compared the performance of the best multi-component GP model with the 1GP model in the derivation of transit parameters of simulated transits. We found that for Jupiter- and Neptune-size planets the best multi-component GP model is slightly better than the 1GP model, and much better than the non-GP model that gives biased results. For Earth-size planets, the 1GP model fails to retrieve the transit because it is a poor description of stellar activity. The non-GP model gives some biased results and the best multi-component GP is capable of retrieving the correct transit model parameters. We conclude that when characterising transiting exoplanets with high signal-to-noise ratios and high cadence light curves, we need models that couple the description of stellar variability with the transits analysis, like GPs. Moreover, for Earth-like exoplanets a better description of stellar variability improves the planetary characterisation.

[24]  arXiv:2001.08007 [pdf, ps, other]
Title: Wind Collision and Accretion Simulations of the Massive Binary System HD 166734
Authors: Amit Kashi (Ariel University)
Comments: Accepted to MNRAS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); High Energy Astrophysical Phenomena (astro-ph.HE)

We run hydrodynamic simulations which follow the colliding winds structure of the massive binary system HD 166734 along its binary orbit, and show that close to periastron passage the secondary wind is suppressed and the secondary accretes mass from the primary wind. The system consists two blue supergiants with masses of $M_1 \approx 39.5 ~\rm{M_\odot}$ and $M_2 \approx 30.5 ~\rm{M_\odot}$, on a $P \simeq 34.538 ~\rm{days}$ orbit with eccentricity of $e \approx 0.618$. This close O-O binary with high eccentricity is observed through its orbit in the X-rays, where it shows an unusual long minimum close to periastron passage. We use advanced simulations with wind acceleration and prescription treatment of accretion and simulate the entire orbit at high resolution that captures the instabilities in the winds. We find that the colliding wind structure is unstable even at apastron. As the stars approach periastron passage the secondary wind is quenched by the primary wind and the accretion onto the secondary begins. The accretion phase lasts for $\simeq 12 ~\rm{days}$, and the amount of accreted mass per cycle we obtain is $M_{\rm{acc}} \simeq 1.3 \cdot 10^{-8} ~\rm{M_\odot}$. The accretion phase can account for the observed decline in X-ray emission from the system.

[25]  arXiv:2001.08087 [pdf, other]
Title: Cold gas and dust: Hunting spiral-like structures in early-type galaxies
Comments: 11 pages, 7 figures, 3 tables, and 4 appendices. Appendices contain dust masses and images of studied galaxies (62). The fits files will be uploaded into the CDS database. Figures in the appendices are of low quality. High-quality images are given in a separated folder. Accepted for publication in A&A
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Observations of neutral hydrogen (HI) and molecular gas show that 50% of all nearby early-type galaxies (ETGs) contain some cold gas. Molecular gas is always found in small gas discs in the central region of the galaxy, while neutral hydrogen is often distributed in a low-column density disc or ring typically extending well beyond the stellar body. Dust is frequently found in ETGs as well. The goal of our study is to understand the link between dust and cold gas in nearby ETGs as a function of HI content. We analyse deep optical $g-r$ images obtained with the MegaCam camera at the Canada-France-Hawaii Telescope for a sample of 21 HI-rich and 41 HI-poor ETGs. We find that all HI-rich galaxies contain dust seen as absorption. Moreover, in 57 percent of these HI-rich galaxies, the dust is distributed in a large-scale spiral pattern. Although the dust detection rate is relatively high in the HI-poor galaxies ($\sim$59 percent), most of these systems exhibit simpler dust morphologies without any evidence of spiral structures. We find that the HI-rich galaxies possess more complex dust morphology extending to almost two times larger radii than HI-poor objects. We measured the dust content of the galaxies from the optical colour excess and find that HI-rich galaxies contain six times more dust (in mass) than HI-poor ones. In order to maintain the dust structures in the galaxies, continuous gas accretion is needed, and the substantial HI gas reservoirs in the outer regions of ETGs can satisfy this need for a long time. We find that there is a good correspondence between the observed masses of the gas and dust, and it is also clear that dust is present in regions further than 3~Reff. Our findings indicate an essential relation between the presence of cold gas and dust in ETGs and offer a way to study the interstellar medium in more detail than what is possible with HI observations.

[26]  arXiv:2001.08106 [pdf, other]
Title: Design and construction of a new detector to measure ultra-low radioactive-isotope contamination of argon
Authors: The DarkSide Collaboration: C. E. Aalseth (1), S. Abdelhakim (2), F. Acerbi (3 and 4), P. Agnes (5), R. Ajaj (6), I. F. M. Albuquerque (7), T. Alexander (1), A. Alici (8 and 9), A. K. Alton (10), P. Amaudruz (11), F. Ameli (12), J. Anstey (6), P. Antonioli (9), M. Arba (13), S. Arcelli (8 and 9), R. Ardito (14 and 15), I. J. Arnquist (1), P. Arpaia (16 and 17), D. M. Asner (18), A. Asunskis (19), M. Ave (7), H. O. Back (1), A. Barrado Olmedo (20), G. Batignani (21 and 22), M. G. Bisogni (21 and 22), V. Bocci (12), A. Bondar (23 and 24), G. Bonfini (25), W. Bonivento (13), E. Borisova (23 and 24), B. Bottino (26 and 27), M. G. Boulay (6), R. Bunker (1), S. Bussino (28 and 29), A. Buzulutskov (23 and 24), M. Cadeddu (30 and 13), M. Cadoni (30 and 13), A. Caminata (27), N. Canci (5 and 25), et al. (291 additional authors not shown)
Comments: 13 pages, 8 figures. Corresponding author: E. S\'anchez Garc\'ia
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Instrumentation and Detectors (physics.ins-det)

Large liquid argon detectors offer one of the best avenues for the detection of galactic weakly interacting massive particles (WIMPs) via their scattering on atomic nuclei. The liquid argon target allows exquisite discrimination between nuclear and electron recoil signals via pulse-shape discrimination of the scintillation signals. Atmospheric argon (AAr), however, has a naturally occurring radioactive isotope, $^{39}$Ar, a $\beta$ emitter of cosmogenic origin. For large detectors, the atmospheric $^{39}$Ar activity poses pile-up concerns. The use of argon extracted from underground wells, deprived of $^{39}$Ar, is key to the physics potential of these experiments. The DarkSide-20k dark matter search experiment will operate a dual-phase time projection chamber with 50 tonnes of radio-pure underground argon (UAr), that was shown to be depleted of $^{39}$Ar with respect to AAr by a factor larger than 1400. Assessing the $^{39}$Ar content of the UAr during extraction is crucial for the success of DarkSide-20k, as well as for future experiments of the Global Argon Dark Matter Collaboration (GADMC). This will be carried out by the DArT in ArDM experiment, a small chamber made with extremely radio-pure materials that will be placed at the centre of the ArDM detector, in the Canfranc Underground Laboratory (LSC) in Spain. The ArDM LAr volume acts as an active veto for background radioactivity, mostly $\gamma$-rays from the ArDM detector materials and the surrounding rock. This article describes the DArT in ArDM project, including the chamber design and construction, and reviews the background required to achieve the expected performance of the detector.

[27]  arXiv:2001.08134 [pdf, other]
Title: Successful application of PSF-R techniques to the case of the globular cluster NGC6121 (M4)
Comments: 5 pages, 4 figures, accepted for publication by A&A Letters
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

Precise photometric and astrometric measurements on astronomical images require an accurate knowledge of the Point Spread Function (PSF). When the PSF cannot be modelled directly from the image, PSF-reconstruction techniques become the only viable solution. So far, however, their performance on real observations has rarely been quantified. Aims. In this Letter, we test the performance of a novel hybrid technique, called PRIME, on Adaptive Optics-assisted SPHERE/ZIMPOL observations of the Galactic globular cluster NGC6121. Methods. PRIME couples PSF-reconstruction techniques, based on control-loop data and direct image fitting performed on the only bright point-like source available in the field of view of the ZIMPOL exposures, with the aim of building the PSF model. Results. By exploiting this model, the magnitudes and positions of the stars in the field can be measured with an unprecedented precision, which surpasses that obtained by more standard methods by at least a factor of four for on-axis stars and by up to a factor of two on fainter, off-axis stars. Conclusions. Our results demonstrate the power of PRIME in recovering precise magnitudes and positions when the information directly coming from astronomical images is limited to only a few point-like sources and, thus, paving the way for a proper analysis of future Extremely Large Telescope observations of sparse stellar fields or individual extragalactic objects.

[28]  arXiv:2001.08139 [pdf, ps, other]
Title: Generation of strong magnetic fields in a nascent neutron star accounting for the chiral magnetic effect
Authors: Maxim Dvornikov (1 and 2), V. B. Semikoz (1), D. D. Sokoloff (3) ((1) IZMIRAN, (2) Tomsk State University, (3) Moscow State University)
Comments: 18 pages, 8 eps figures, LaTeX2e. arXiv admin note: text overlap with arXiv:1909.03236
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Phenomenology (hep-ph)

We propose the mean field dynamo model for the generation of strongest magnetic fields, $B\sim 10^{15}\,{\rm G}$, in a neutron star (NS) accounting for the chiral magnetic effect (CME) driven by the shock in a supernova (SN) progenitor of that NS. The temperature jump at a narrow shock front, where an initial magnetic field existing in inflowing matter rises sharply, is the source of the CME that prevails significantly the erasure of the CME due to the spin-flip through Coulomb collisions in plasma. The growth of the magnetic field just behind the shock given by the instability term $\nabla\times (\alpha {\bf B})$ in induction equation, stops after a successful SN explosion that throws out the mantle of a protoneutron star. As a result, such an explosion interrupts the transfer of strongly magnetized plasma from the shock onto NS surface and leads to the saturation of the magnetic field. Assuming the rigid protostar rotation, we employ the mean field dynamo, which is similar to the $\alpha^2$-dynamo known in the standard magnetohydrodynamics (MHD). The novelty of our model is that $\alpha^2$-dynamo is based on concepts of particle physics, applied in MHD, rather than by a mirror asymmetry of convective vortices in the rotating convection.

[29]  arXiv:2001.08147 [pdf, other]
Title: GG Tau A: gas properties and dynamics from the cavity to the outer disk
Comments: 18 pages, 14 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA)

We used new ALMA $^{13}$CO and C$^{18}$O(3-2) observations obtained at high angular resolution ($\sim$0.2") together with previous CO(3-2) and (6-5) ALMA data and continuum maps at 1.3 and 0.8 mm in order to determine the gas properties (temperature, density, and kinematics) in the cavity and to a lesser extent in the outer disk of GG Tau A, the prototype of a young triple T Tauri star that is surrounded by a massive and extended Keplerian outer disk. By deprojecting, we studied the radial and azimuthal gas distribution and its kinematics. We also applied a new method to improve the deconvolution of the CO data and in particular better quantify the emission from gas inside the cavity. We perform local and nonlocal thermodynamic equilibrium studies in order to determine the excitation conditions and relevant physical parameters inside the ring and in the central cavity. Residual emission after removing a smooth-disk model indicates unresolved structures at our angular resolution, probably in the form of irregular rings or spirals. The outer disk is cold, with a temperature $<20$ K beyond 250 au that drops quickly (r$^{-1}$). The kinematics of the gas inside the cavity reveals infall motions at about 10% of the Keplerian speed. We derive the amount of gas in the cavity, and find that the brightest clumps, which contain about 10% of this mass, have kinetic temperatures 40$-$80 K, CO column densities of a few 10$^{17}$ cm$^{-2}$, and H$_2$ densities around 10$^7$ cm$^{-3}$. Although the gas in the cavity is only a small fraction of the disk mass, the mass accretion rate throughout the cavity is comparable to or higher than the stellar accretion rate. It is accordingly sufficient to sustain the circumstellar disks on a long timescale.

[30]  arXiv:2001.08182 [pdf, other]
Title: New constraints on the structure of the nuclear stellar cluster of the Milky Way from star counts and MIR imaging
Comments: 20 pages
Subjects: Astrophysics of Galaxies (astro-ph.GA)

The Milky Way nuclear star cluster (MWNSC) is a crucial laboratory for studying the galactic nuclei of other galaxies, but its properties have not been determined unambiguously until now. Aims. We aim to study the size and spatial structure of the MWNSC. Methods. This study uses data and methods that address potential shortcomings of previous studies on the topic. We use $0.2''$ angular resolution $K_{s}$ data to create a stellar density map in the central $86.4$pc x $21$pc at the Galactic center. We include data from selected adaptive-optics-assisted images obtained for the inner parsecs. In addition, we use IRAC/Spitzer mid-infrared (MIR) images. We model the Galactic bulge and the nuclear stellar disk in order to subtract them from the MWNSC. Finally, we fit a S\'ersic model to the MWNSC and investigate its symmetry. Results. Our results are consistent with previous work. The MWNSC is flattened with an axis ratio of $q=0.71 \pm0.10$, an effective radius of $R_{e}=(5.1 \pm1.0)$ pc, and a S\'ersic index of $n=2.2 \pm0.7$. Its major axis may be tilted out of the Galactic plane by up to $-10$ degrees. The distribution of the giants brighter than the Red Clump (RC) is found to be significantly flatter than the distribution of the faint stars. We investigate the 3D structure of the central stellar cusp using our results on the MWNSC structure on large scales to constrain the deprojection of the measured stellar surface number density, obtaining a value of the 3D inner power law of $\gamma=1.38\pm0.06_{sys}\pm0.01_{stat}$. Conclusions. The MWNSC shares its main properties with other extragalactic NSCs found in spiral galaxies. The differences in the structure between bright giants and RC stars might be related to the existence of not completely mixed populations of different ages. This may hint at recent growth of the MWNSC through star formation or cluster accretion.

[31]  arXiv:2001.08197 [pdf, other]
Title: Reproducing the CO-to-H$_2$ conversion factor in cosmological simulations of Milky Way-mass galaxies
Comments: Submitted to MNRAS. 14 pages, 10 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present models of CO(1-0) emission from Milky Way-mass galaxies at redshift zero in the FIRE-2 cosmological zoom-in simulations. We calculate the molecular abundances by post-processing the simulations with an equilibrium chemistry solver while accounting for the effects of local sources, and determine the emergent CO(1-0) emission using a line radiative transfer code. We find that the results depend strongly on the shielding length assumed, which in our models sets the attenuation of the incident UV radiation field. Commonly used choices for the shielding length, such as the Jeans length, result in CO abundances that are too high at a given H$_2$ abundance. We find that a model with a distribution of shielding lengths, which has a median shielding length of $\sim 3$ pc in cold gas ($T < 300$ K) for both CO and H$_{2}$, is able to reproduce both the observed CO(1-0) luminosity and inferred CO-to-H$_{2}$ conversion factor at a given star formation rate compared with observations. We suggest that this short shielding length can be thought of as a subgrid model which controls the amount of radiation that penetrates giant molecular clouds.

[32]  arXiv:2001.08208 [pdf, other]
Title: Searching for Ultra-fast Outflows in AGN using Variability Spectra
Comments: 23 pages, 13 figures, accepted for publication in MNRAS
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We present a qualitative search for ultra-fast outflows (UFOs) in excess variance spectra of radio-quiet active galactic nuclei (AGN). We analyse 42 sources from the Tombesi et al. (2010) spectroscopic UFO detection sample, and an additional 22 different sources from the Kara et al. (2016) variability sample. A total of 58 sources have sufficient observational data from XMM-Newton EPIC-pn and variability for an excess variance spectrum to be calculated. We examine these spectra for peaks corresponding to variable blue-shifted H- and He-like ion absorption lines from UFOs. We find good evidence for such outflows in 28% of the AGN sample and weak evidence in a further 31%, meaning that $\sim$ 30-60% of the AGN sample hosts such UFOs. The mean and median blue-shifted velocity is found to be $\sim$ 0.14c and 0.12c, respectively. Current variability methods allow for a fast, model-independent determination of UFOs, however, further work needs to be undertaken to better characterize the statistical significance of the peaks in these spectra by more rigorous modelling. Detecting good evidence for variable UFO lines in a large number of sources also lays the groundwork for detailed analysis of the variability timescales of the absorbers. This will allow us to probe their densities and hence distances from the central super-massive black hole.

Cross-lists for Thu, 23 Jan 20

[33]  arXiv:2001.07945 (cross-list from gr-qc) [pdf, ps, other]
Title: Testing the equation of state for viscous dark energy
Comments: 13 pages, 3 figures. To be published in PRD
Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Some cosmological scenarios with bulk viscosity for the dark energy fluid are considered. Based on some considerations related to hydrodynamics, two different equations of state for dark energy are assumed, leading to power-law and logarithmic effective corrections to the pressure. The models are tested with the latest astronomical data from Type Ia supernovae (Pantheon sample), measurements of the Hubble parameter $H(z)$,
Baryon Acoustic Oscillations and Cosmic Microwave Background radiation. In comparison with $\Lambda$CDM model, some different results are obtained and their viability is discussed. The power-law model shows some modest results, achieved under negative values of bulk viscosity, while the logarithmic scenario provide good fits in comparison to $\Lambda$CDM model.

[34]  arXiv:2001.07953 (cross-list from physics.flu-dyn) [pdf, other]
Title: Generation of shear flows and vortices in rotating anelastic convection
Comments: 18 pages, 12 figures. Submitted to Physical Review Fluids
Subjects: Fluid Dynamics (physics.flu-dyn); Solar and Stellar Astrophysics (astro-ph.SR)

We consider the effect of stratification on systematic, large-scale flows generated in anelastic convection. We present results from three-dimensional numerical simulations of convection in a rotating plane layer in which the angle between the axis of rotation and gravity is allowed to vary. This model is representative of different latitudes of a spherical body. We consider two distinct parameter regimes: (i) weakly rotating and (ii) rapidly rotating. In each case, we examine the effect of stratification on the flow structure and heat transport properties focussing on the difference between Boussinesq and anelastic convection. Furthermore, we show that regimes (i) and (ii) generate very different large-scale flows and we investigate the role stratification has in modifying these flows. The stratified flows possess a net helicity not present in the Boussinesq cases which we suggest, when combined with the self-generated shear flows, could be important for dynamo action.

[35]  arXiv:2001.08036 (cross-list from hep-ph) [pdf, other]
Title: Relativistic hypernuclear compact stars with calibrated equations of state
Comments: Accepted for publication by Phys.Rev.D. Supplemental material not included
Subjects: High Energy Physics - Phenomenology (hep-ph); High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)

Within the covariant density functional theory of hypernuclear matter we build a series of equations of state for hypernuclear compact stars, by calibrating the coupling constants of the $\Xi$-hyperon to the experimental binding energy of the single-$\Xi$ hypernuclei $^{15}_{\Xi^-}$C and $^{12}_{\Xi^-}$Be. Coupling constants of the $\Lambda$-hyperon to nucleons have been calibrated on a vast collection of experimental data on single $\Lambda$ hypernuclei in Fortin et al. 2017, 2018 and Provid\^encia et al. 2019, and we employ those values. Uncertainties on the couplings of the $\Sigma$-hyperon to nuclear matter, due to lack of experimental data, are accounted for by allowing for a wide variation of the well depth of $\Sigma$ at rest in symmetric saturated nuclear matter. To account for uncertainties in the nucleonic sector at densities much larger than the saturation density, a rich collection of parameterizations is employed, some of them in agreement with existing constraints from nuclear physics and astrophysics. Neutron star properties are investigated with all these calibrated equations of state. The effects of the presence of hyperons on the radius, on the tidal deformability, on the moment of inertia, and on the nucleonic direct Urca process are discussed. The sensitivity of the hyperonic direct Urca processes to uncertainties in the nucleonic and hyperonic sectors is also addressed. It is shown that the relative variations of the radius, tidal deformability and moment of inertia from the values that characterize purely nucleonic stars are linearly correlated with the strangeness fraction. The maximum radius deviation, obtained for most massive neutron stars, are $\approx 10\%$. The reduction of the maximum mass, triggered by nucleation of strangeness, is estimated at $\approx 15 - 20\%$, out of which $5\%$ comes from insufficient information on the $\Sigma$-hyperon interactions.

[36]  arXiv:2001.08206 (cross-list from nucl-ex) [pdf, other]
Title: Decay properties of $^{22}\mathrm{Ne} + α$ resonances and their impact on $s$-process nucleosynthesis
Comments: 17 pages, 4 figures, accepted for publication in Phys. Lett. B
Subjects: Nuclear Experiment (nucl-ex); Solar and Stellar Astrophysics (astro-ph.SR); Nuclear Theory (nucl-th)

The astrophysical $s$-process is one of the two main processes forming elements heavier than iron. A key outstanding uncertainty surrounding $s$-process nucleosynthesis is the neutron flux generated by the ${}^{22}\mathrm{Ne}(\alpha, n){}^{25}\mathrm{Mg}$ reaction during the He-core and C-shell burning phases of massive stars. This reaction, as well as the competing ${}^{22}\mathrm{Ne}(\alpha, \gamma){}^{26}\mathrm{Mg}$ reaction, is not well constrained in the important temperature regime from ${\sim} 0.2$--$0.4$~GK, owing to uncertainties in the nuclear properties of resonances lying within the Gamow window. To address these uncertainties, we have performed a new measurement of the ${}^{22}\mathrm{Ne}({}^{6}\mathrm{Li}, d){}^{26}\mathrm{Mg}$ reaction in inverse kinematics, detecting the outgoing deuterons and ${}^{25,26}\mathrm{Mg}$ recoils in coincidence. We have established a new $n / \gamma$ decay branching ratio of $1.14(26)$ for the key $E_x = 11.32$ MeV resonance in $^{26}\mathrm{Mg}$, which results in a new $(\alpha, n)$ strength for this resonance of $42(11)~\mu$eV when combined with the well-established $(\alpha, \gamma)$ strength of this resonance. We have also determined new upper limits on the $\alpha$ partial widths of neutron-unbound resonances at $E_x = 11.112,$ $11.163$, $11.169$, and $11.171$ MeV. Monte-Carlo calculations of the stellar ${}^{22}\mathrm{Ne}(\alpha, n){}^{25}\mathrm{Mg}$ and ${}^{22}\mathrm{Ne}(\alpha, \gamma){}^{26}\mathrm{Mg}$ rates, which incorporate these results, indicate that both rates are substantially lower than previously thought in the temperature range from ${\sim} 0.2$--$0.4$~GK.

Replacements for Thu, 23 Jan 20

[37]  arXiv:1902.03294 (replaced) [pdf, other]
Title: The Transverse-Traceless Spin-2 Gravitational Wave Cannot Be A Standalone Observable Because It Is Acausal
Comments: 64 pages, 1 figure, 4D Minkowski results summarized in Sec. VI, version accepted by CQG
Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th)
[38]  arXiv:1902.06438 (replaced) [pdf, other]
Title: Rotational Desorption of Ice Mantles and Complex Molecules from Suprathermally Rotating Dust Grains around Young Stellar Objects
Comments: 17 pages, 11 figures; accepted to ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA); Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
[39]  arXiv:1904.04142 (replaced) [pdf, ps, other]
Title: The masses and shadows of the black holes Sagittarius A* and M87* in modified gravity (MOG)
Comments: 4 pages, 2 figures, updated to match edits in published version
Journal-ref: Phys. Rev. D 101, 024014 (2020)
Subjects: General Relativity and Quantum Cosmology (gr-qc); Astrophysics of Galaxies (astro-ph.GA)
[40]  arXiv:1907.08995 (replaced) [pdf, other]
Title: Strongly magnetized accretion disks: structure and accretion from global magnetohydrodynamic simulations
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)
[41]  arXiv:1907.13484 (replaced) [pdf, other]
Title: Detection of cross-correlation between gravitational lensing and gamma rays
Comments: 24 pages, 10 figures, v2: text re-arranged, typos corrected, slight improvement in the detection significance, matching version accepted for publication in PRL
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE)
[42]  arXiv:1908.04656 (replaced) [pdf, other]
Title: Search for Point-Like TeV Sources in the Large Magellanic Cloud
Comments: 8 pages, 5 figures, 3 tables, 36th International Cosmic Ray Conference 2019 The proceedings have been updated on 2020/01/22. In the original version the upper limits on the luminosity and derived values were wrongly calculated
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)
[43]  arXiv:1908.06042 (replaced) [pdf, other]
Title: Thermomagnetic Ettingshausen-Nernst effect in tachocline, magnetic reconnection phenomenon in lower layers, axion mechanism of solar luminosity variations, coronal heating problem solution and mechanism of ADM variations around BH
Comments: 159 pages, 38 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)
[44]  arXiv:1908.08952 (replaced) [pdf, other]
Title: Gravity and the Nonlinear Growth of Structure in the Carnegie-Spitzer-IMACS Redshift Survey
Comments: 13 pages, 12 figures, submitted to Monthly Notices of the Royal Astronomical Society, 23 August 2019, and accepted for publication, 9 January 2020. Some more typo(s) fixed
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA)
[45]  arXiv:1909.03736 (replaced) [pdf, other]
Title: Measurement of Void Bias Using Separate Universe Simulations
Comments: 16 pages, 11 figures. Match to the published version
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)
[46]  arXiv:1910.07760 (replaced) [pdf, ps, other]
Title: What Would Happen If We Were About 1 pc Away from a Supermassive Black Hole?
Authors: Lorenzo Iorio
Comments: LaTex2e, 17 pages, no tables, 3 figures. Version matching the one published in The Astrophysical Journal (ApJ)
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA); General Relativity and Quantum Cosmology (gr-qc)
[47]  arXiv:1911.04459 (replaced) [pdf, other]
Title: On the inflationary massive field with a curved field manifold
Authors: Dong-Gang Wang
Comments: 23 pages, 5 figures; v2: published version with minor revisions and references added
Journal-ref: JCAP 01 (2020) 046
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)
[48]  arXiv:1911.04504 (replaced) [pdf, other]
Title: Towards a precision calculation of the effective number of neutrinos $N_{\rm eff}$ in the Standard Model I: The QED equation of state
Comments: 25 pages, plus appendices and 8 figures; v2: references added, version accepted by JCAP
Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Nongalactic Astrophysics (astro-ph.CO)
[49]  arXiv:1911.08475 (replaced) [pdf, other]
Title: The Gravitational Lensing Signatures of BOSS Voids in the Cosmic Microwave Background
Comments: 20 pages, 8 figures, 3 tables; addressed minor comments from the reviewer; accepted for publication in ApJ
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)
[50]  arXiv:1912.03239 (replaced) [pdf, other]
Title: VLT/XShooter spectroscopy of Lyman Break Analogs: direct method O/H abundances and nitrogen enhancements
Comments: ApJ, accepted (25 pages, 21 figures)
Subjects: Astrophysics of Galaxies (astro-ph.GA)
[51]  arXiv:1912.03255 (replaced) [pdf, other]
Title: Embedded operator splitting methods for perturbed systems
Authors: Hanno Rein
Comments: 8 pages, 5 figures, accepted for publication by MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM); Dynamical Systems (math.DS)
[52]  arXiv:1912.04301 (replaced) [pdf, other]
Title: Constraints on Aquatic Photosynthesis for Terrestrial Planets Around Other Stars
Comments: Published in The Astrophysical Journal Letters; 7 pages; 3 figures
Journal-ref: The Astrophysical Journal Letters, Vol. 889, L15 (2020)
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
[53]  arXiv:1912.08698 (replaced) [pdf, ps, other]
Title: Short gamma-ray bursts within 200 Mpc
Comments: 13 pages, 9 figures, 1 table, accepted for publication in MNRAS
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)
[54]  arXiv:1912.12886 (replaced) [pdf, other]
Title: Infrared Properties of Asymptotic Giant Branch Stars in Our Galaxy and the Magellanic Clouds
Authors: Kyung-Won Suh
Comments: 25 pages, 20 figures, accepted for publication in ApJ
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)
[55]  arXiv:2001.01221 (replaced) [pdf, other]
Title: Global time-regularization of the gravitational $N$-body problem
Comments: 25 pages; acknowledgments added; remarks 5 and 7 added
Subjects: Dynamical Systems (math.DS); Earth and Planetary Astrophysics (astro-ph.EP)
[56]  arXiv:2001.01336 (replaced) [pdf, other]
Title: Modeling the upper kHz QPOs of 4U 1728-34 with X-ray reverberation
Comments: Accepted for publication in ApJ. 16 pages, 7 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)
[57]  arXiv:2001.01369 (replaced) [pdf, other]
Title: The Roles of Mass and Environment in the Quenching of Galaxies. II
Comments: 13 pages, 8 figures, accepted for publication in ApJ, minor revision after Proof correction
Subjects: Astrophysics of Galaxies (astro-ph.GA)
[58]  arXiv:2001.06123 (replaced) [pdf, other]
Title: Using multi-line spectropolarimetric observations of forbidden emission lines to measure single-point coronal magnetic fields
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Applied Physics (physics.app-ph)
[59]  arXiv:2001.06904 (replaced) [pdf, other]
Title: UV & U-band luminosity functions from CLAUDS and HSC-SSP -- I. Using four million galaxies to simultaneously constrain the very faint and bright regimes to $z \sim 3$
Comments: 18 pages, 11 figures (26 pages, 18 figures including the Appendix). Submitted to MNRAS. Revised version
Subjects: Astrophysics of Galaxies (astro-ph.GA)
[60]  arXiv:2001.06926 (replaced) [pdf, other]
Title: Supernova Magnitude Evolution and PAge Approximation
Authors: Zhiqi Huang
Comments: fixed a typo 120Gyr-&gt;12Gyr
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)
[61]  arXiv:2001.07257 (replaced) [pdf, other]
Title: The extreme CNO-enhanced composition of the primitive iron-poor dwarf star J0815+4729
Comments: Accepted for publication in The Astrophysical Journal Letters
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)
[62]  arXiv:2001.07665 (replaced) [pdf, other]
Title: Extracting high-level information from gamma-ray burst supernova spectra
Comments: Accepted for publication in MNRAS, minor updates from previous version
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)
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