65 articles on Sunday, March 24

arXiv:1903.08653v1 [pdf, other]
Gravitational Waves, Extreme Astrophysics, and Fundamental Physics with Precision Pulsar Timing
Comments: Submitted to the Astro2020 Decadal Survey. One of 5 core white-papers authored by members of the NANOGrav Collaboration. 10 pages, 3 figures

Precision pulsar timing at the level of tens to hundreds of nanoseconds allows detection of nanohertz gravitational waves (GWs) from supermassive binary black holes (SMBBHs) at the cores of merging galaxies and, potentially, from exotic sources such as cosmic strings. The same timing data used for GW astronomy also yield precision masses of neutron stars orbiting other compact objects, constraints on the equation of state of nuclear matter, and precision tests of General Relativity, the Strong Equivalence Principle, and alternative theories of gravity. Timing can also lead to stringent constraints on the photon mass and on changes in fundamental constants and could reveal low mass objects (rogue planets, dark matter clumps) that traverse pulsar lines of sight. Data sets also allow modeling of the density, magnetic field, and turbulence in the interstellar plasma. Roughly 100 millisecond pulsars (MSPs) are currently being timed at $\sim$GHz frequencies using the largest radio telescopes in the world. These data sets currently represent ~1000 pulsar-years and will increase dramatically over the next decade. These topics are presented as a program of key science with flowdown technical requirements for achieving the science.

arXiv:1903.08657v1 [pdf, other]
A 2019 Cosmic UV/X-ray Background Model Update
Comments: 16 pages, 10 figures, submitted. Electronic data available at http://galaxies.northwestern.edu/uvb

We present an updated model of the cosmic ionizing background from the UV to the X-rays. Relative to our previous model (Faucher-Giguere et al. 2009), the new model provides a better fit to a large number of up-to-date empirical constraints, including: 1) new galaxy UV luminosity functions; 2) stellar spectra including binary stars; 3) recent escape fraction measurements; 4) a measurement of the non-ionizing UV background; 5) obscured and unobscured AGN; 6) measurements of the intergalactic HI and HeII photoionization rates at z~0-6; and 7) the local X-ray background. In this model, AGN dominate the HI ionizing background at z<3 and star-forming galaxies dominate it at higher redshifts. Combined with the large AGN contribution at low redshifts and the steeply declining AGN luminosity function beyond z~2, the slow evolution of the HI ionization rate inferred from the HI Lya forest requires an escape fraction from star-forming galaxies that increases strongly with redshift. Our new UV background model implies a best-fit escape fraction of 7% at z=3. We provide effective photoionization and photoheating rates calibrated to match the Planck 2018 reionization optical depth and recent constraints from the HeII Lya forest.

arXiv:1903.08659v1 [pdf, other]
The evolution of the cosmic molecular gas density
Comments: 7 pages, 2 figures, Science White paper submitted to Astro2020 Decadal Survey

One of the last missing pieces in the puzzle of galaxy formation and evolution through cosmic history is a detailed picture of the role of the cold gas supply in the star-formation process. Cold gas is the fuel for star formation, and thus regulates the buildup of stellar mass, both through the amount of material present through a galaxy's gas mass fraction, and through the efficiency at which it is converted to stars. Over the last decade, important progress has been made in understanding the relative importance of these two factors along with the role of feedback, and the first measurements of the volume density of cold gas out to redshift 4, (the "cold gas history of the Universe") has been obtained. To match the precision of measurements of the star formation and black-hole accretion histories over the coming decades, a two orders of magnitude improvement in molecular line survey speeds is required compared to what is possible with current facilities. Possible pathways towards such large gains include significant upgrades to current facilities like ALMA by 2030 (and beyond), and eventually the construction of a new generation of radio-to-millimeter wavelength facilities, such as the next generation Very Large Array (ngVLA) concept.

arXiv:1903.08661v1 [pdf, other]
Observational constraints on the survival of pristine stars
Comments: 5 pages, 2 figures, submitted to MNRAS, comments welcome

There is a longstanding discussion about whether low mass stars can form from pristine gas in the early Universe. A particular point of interest is whether we can find surviving pristine stars from the first generation in our local neighbourhood. We present here a simple analytical estimate that puts tighter constraints on the existence of such stars.In the conventional picture, should these stars have formed in significant numbers and have preserved their pristine chemical composition until today, we should have found them already.

arXiv:1903.08662v1 [pdf, other]
Imprints of Mass Accretion History on the Shape of the Intracluster Medium and the $T_X-M$ Relation
Comments: 10 pages, 7 figures, comments welcome

We use a statistical sample of galaxy clusters from a large cosmological $N$-body$+$hydrodynamics simulation to examine the relation between morphology, or shape, of the X-ray emitting intracluster medium (ICM) and the mass accretion history of the galaxy clusters. We find that the mass accretion rate (MAR) of a cluster is correlated with the ellipticity of the ICM. The correlation is largely driven by material accreted in the last $\sim 4.5$~Gyr, indicating a characteristic time-scale for relaxation of cluster gas. Furthermore, we find that the ellipticity of the outer regions ($R\sim R_{\rm 500c}$) of the ICM is correlated with the overall MAR of clusters, while ellipticity of the inner regions ($\lesssim 0.5 R_{\rm 500c}$) is sensitive to recent major mergers with mass ratios of $\geq 1:3$. Finally, we examine the impact of variations in cluster mass accretion history on the X-ray observable-mass scaling relations. We show that there is a {\it continuous\/} anti-correlation between the residuals in the $T_x-M$ relation and cluster MARs, within which merging and relaxed clusters occupy extremes of the distribution rather than form two peaks in a bi-modal distribution, as was often assumed previously. Our results indicate the systematic uncertainties in the X-ray observable-mass relations can be mitigated by using the information encoded in the apparent ICM ellipticity.

arXiv:1903.08665v1 [pdf, other]
ASASSN-18tb: A Most Unusual Type Ia Supernova Observed by TESS and SALT
Comments: 13 pages, 8 figures. Submitted to MNRAS

We present photometric and spectroscopic observations of the unusual Type Ia supernova ASASSN-18tb, including a series of SALT spectra obtained over the course of nearly six months and the first observations of a supernova by the Transiting Exoplanet Survey Satellite (TESS). We confirm a previous observation by Kollmeier et al. (2019) showing that ASASSN-18tb is the first relatively normal Type Ia supernova to exhibit clear broad ($\sim1000$ km s$^{-1}$) H$\alpha$ emission in its nebular phase spectra. We find that this event is best explained as a sub-Chandrasekhar mass explosion with $M_{Ni} \approx 0.27\; \rm{M}_\odot$. Despite the strong H$\alpha$ signature at late times, we find that the early rise of the supernova shows no evidence for deviations from a single-component power-law and is best fit with a moderately shallow power-law of index $1.40\pm0.03$. We find that the H$\alpha$ luminosity remains approximately constant after its initial detection at phase +37 d, and that the H$\alpha$ velocity evolution does not trace that of the Fe~III$~\lambda4660$ emission. These suggest that the H$\alpha$ emission arises from circumstellar medium (CSM) rather than swept up material from a non-degenerate companion. However, ASASSN-18tb is strikingly different from other known CSM-interacting Type Ia supernovae in a number of significant ways. Those objects typically show an H$\alpha$ luminosity two orders of magnitude higher than what is seen in ASASSN-18tb, pushing them away from the empirical light-curve relations that define "normal" Type Ia supernovae. Conversely, ASASSN-18tb exhibits a fairly typical light curve and luminosity for an underluminous or transitional SN Ia, with $M_R \approx -18.1$ mag. Moreover, ASASSN-18tb is the only SN Ia showing H$\alpha$ from CSM interaction to be discovered in an early-type galaxy.

arXiv:1903.08669v1 [pdf, other]
New Insights into the Physical Conditions and Internal Structure of a Candidate Proto-Globular Cluster
Comments: 18 pages, 14 figures, Accepted to ApJ 2019 March 4

We present $\sim$0.1" resolution ($\sim$10 pc) ALMA observations of a molecular cloud identified in the merging Antennae galaxies with the potential to form a globular cluster, nicknamed the ''Firecracker.' Since star formation has not yet begun at an appreciable level, this cloud provides an example of what the birth environment of a globular cluster may have looked like before stars form and disrupt the natal conditions. Using emission from $^{12}$CO(2-1), $^{12}$CO(3-2), $^{13}$CO(2-1), HCN(4-3), and HCO$^+$(4-3), we are able to resolve the cloud's structure and find that it has a characteristic radius of 22 pc and a mass of 1--9$\times10^6 M_\odot$. We also constrain the abundance ratios of $^{12}$CO/$^{13}$CO and H$_2$/\twelveCO. Based on the calculated mass, we determine that the commonly used CO-to-H$_2$ conversion factor varies spatially, with average values in the range $X_{CO}=(0.12-1.1)\times10^{20}$ cm$^{-2}$ (K km s$^{-1}$)$^{-1}$. We demonstrate that if the cloud is bound (as is circumstantially suggested by its bright, compact morphology), an external pressure of $P/k > 10^8$ K cm$^{-3}$ is required. This would be consistent with theoretical expectations that globular cluster formation requires high pressure environments. The position-velocity diagram of the cloud and its surrounding material suggests that this pressure may be produced by the collision of filaments. The radial profile of the column density can be fit with both a Gaussian and Bonnor-Ebert profile. The relative line strengths of HCN and HCO$^+$ in this region suggest that these molecular lines can be used as tracers for the evolutionary stage of a cluster.

arXiv:1903.08670v1 [pdf, other]
Astro2020 Science White Paper: The Local Relics of of Supermassive Black Hole Seeds
Comments: Science White Paper Submitted for the Astro2020 Decadal Survey on Astronomy and Astrophysics

We have compelling evidence for stellar-mass black holes (BHs) of ~5-80 M_sun that form through the death of massive stars. We also have compelling evidence for so-called supermassive BHs (10^5-10^10 M_sun) that are predominantly found in the centers of galaxies. We have very good reason to believe there must be BHs with masses in the gap between these ranges: the first ~10^9 M_sun BHs are observed only hundreds of millions of years after the Big Bang, and all theoretically viable paths to making supermassive BHs require a stage of "intermediate" mass. However, no BHs have yet been reliably detected in the 100-10}^5 M_sun mass range. Uncovering these intermediate-mass BHs of 10^3-10^5 M_sun is within reach in the coming decade. In this white paper we highlight the crucial role that 30-m class telescopes will play in dynamically detecting intermediate-mass black holes, should they exist.

arXiv:1903.08675v1 [pdf, other]
Cosmic compass - First tomography of an outer 3D sub-Gauss field via atomic alignment
Comments: No comment found

Sub-Gauss magnetic fields are crucial for many physical processes from Galactic $kpc$ scale to stellar $Au$ scale, but are nontrivial to detect. All present magnetic diagnoses trace only one component of a magnetic field at best. Here we report the first observational results that unveil 3D topology as well as the strength of a sub-milliGauss magnetic field beyond our solar system. We found that two weak neutral iron absorption lines from the ground state in the atmosphere of $89~Her$ produced counterintuitive high-amplitude polarizations and consistent polarization angles, exactly in line with the theoretical prediction from ground state alignment (GSA). Our analysis reveals the first sub-AU scale magnetic field on $89~Her$, that is $1.3kpc$ away, has a 3D orientation aligned to the stellar outflow axis and a strength of $70\mu{G} \lesssim B \lesssim150\mu{G}$, thus substantially improving the accuracy by five orders of magnitude compared to the previous $10G$ upper limit set by non-detection of Zeeman effect. This long-awaited discovery is anticipated to usher in a new era of precise measurement of sub-gauss magnetic field in the Universe.

arXiv:1903.08681v1 [pdf, other]
Towards observing reverberating and superefficient pulsar wind nebulae
Comments: Accepted for publication in MNRAS

In a recent work, we numerically studied the radiative properties of the reverberation phase of pulsar wind nebulae (PWNe), i.e., when the reverse shock created by the supernova explosion travels back towards the pulsar, compressing the wind bubble. We focused on several well-characterized PWNe and used them as examples for introducing the concept of superefficiency. The latter is a period of the PWN evolution, happening within reverberation, where the luminosity in a given band exceeds the spin-down power at the time. Here, we explore a broad range of PWN models to study their reverberation and superefficiency phases in a systematic way. Armed with these models we consider two aspects: On the one hand, we analyze via Monte Carlo simulations how many Galactic PWNe are expected to be reverberating or in a superefficiency stage at any given time, providing the first such estimations. On the other hand, we focus on searching for observational signatures of such periods. We analyze archival observations and check for the existence of possible candidates for superefficient PWNe. We also provide predictions for the future evolution of the magnetar nebula J1834.9-0846 (which we consider to be starting its reverberation period) along the next 50 years. Using our simulations as input we study how sensitive current and future X-ray satellites (like eXTP or Athena) will be to observe such evolution, concluding that they will be able to track it in detail.

arXiv:1903.08692v1 [pdf, other]
The parallelism between galaxy clusters and early-type galaxies: I. The light and mass profiles
Comments: 25 pages, 19 figures

We have analyzed the parallelism between the properties of galaxy clusters and early-type galaxies (ETGs) by looking at the similarity between their light profiles. We find that the equivalent luminosity profiles of all these systems in the \vfilt\ band, once normalized to the effective radius \re\ and shifted in surface brightness, can be fitted by the S\'ersic's law \Sers\ and superposed with a small scatter ($\le0.3$ mag). By grouping objects in different classes of luminosity, the average profile of each class slightly deviates from the other only in the inner and outer regions (outside $0.1\leq r/R_e\leq 3$), but the range of values of $n$ remains ample for the members of each class, indicating that objects with similar luminosity have quite different shapes. The "Illustris" simulation reproduces quite well the luminosity profiles of ETGs, with the exception of in the inner and outer regions where feedback from supernovae and active galactic nuclei, wet and dry mergers, are at work. The total mass and luminosity of galaxy clusters as well as their light profiles are not well reproduced. By exploiting simulations we have followed the variation of the effective half-light and half-mass radius of ETGs up to $z=0.8$, noting that progenitors are not necessarily smaller in size than current objects. We have also analyzed the projected dark+baryonic and dark-only mass profiles discovering that after a normalization to the half-mass radius, they can be well superposed and fitted by the S\'ersic's law.

arXiv:1903.08696v1 [pdf, other]
MUSE observations of a changing-look AGN I: The re-appearance of the broad emission lines
Comments: Accepted for publication in MNRAS

Optical changing-look Active Galactic Nuclei (AGN) are a class of sources that change type within a short timescale of years or decades. This change is characterised by the appearance or disappearance of broad emission lines, often associated with dramatic AGN continuum flux changes that are orders of magnitude larger than those expected from typical AGN variability. In this work we study for the first time the host galaxy of a changing-look AGN, Mrk 590, using high spatial resolution optical and near-infrared observations. We discover that after ~ 10 yr absence, the optical broad emission lines of Mrk 590 have reappeared. The AGN optical continuum flux however, is still ~ 10 times lower than that observed during the most luminous state in the 1990s. The host galaxy shows a 4.5 kpc radius star-forming ring with knots of ionised and cold molecular gas emission. Extended ionised and warm molecular gas emission are detected in the nucleus, indicating that there is a reservoir of gas as close as 60 pc from the black hole. We observe a nuclear gas spiral between radii r ~ 0.5 - 2 kpc, which has been suggested as a dynamical mechanism able to drive the necessary gas to fuel AGN. We also discover blue-shifted and high velocity dispersion [O III] emission out to a radius of 1 kpc, tracing a nuclear gas outflow. The gas dynamics in Mrk 590 suggest a complex balance between gas inflow and outflow in the nucleus of the galaxy.

arXiv:1903.08705v1 [pdf, other]
Spectrophotometric redshifts for $\mathrm{z\sim1}$ galaxies and predictions for number densities with WFIRST and Euclid
Comments: 15 pages, 8 figures. Submitted to ApJ. Comments welcome

We investigate the accuracy of 4000\AA/Balmer-break based redshifts by combining Hubble Space Telescope ({\it HST}) grism data with photometry. The grism spectra are from the Probing Evolution And Reionization Spectroscopically (PEARS) survey with {\it HST} using the G800L grism on the Advanced Camera for Surveys (ACS). The photometric data come from a compilation by the 3D-HST collaboration of imaging from multiple surveys (notably CANDELS and 3D-HST). We show evidence that spectrophotometric redshifts (SPZs) typically improve on the accuracy of photometric redshifts by $\sim$16--60\%. We show that the robustness of the SPZ is directly related to the fidelity of the D4000 measurement. We also estimate the accuracy of continuum-based redshifts, i.e., for galaxies that do not contain strong emission lines, based on the grism data alone ($\sigma^\mathrm{NMAD}_{\Delta z/(1+z)}{\lesssim}0.06$). Given that future space-based observatories like WFIRST and Euclid will spend a significant fraction of time on slitless spectroscopic observations, we estimate number densities for objects with a redshift accuracy $\leq$0.02. We predict $\sim$8200 galaxies/degree$^2$ for galaxies with D4000$>$1.1 and a redshift accuracy of $\leq$2\% to a limit of $i_{AB}$$\sim$24 mag. This is \emph{especially} important in the absence of an accompanying rich photometric dataset like the existing one for the CANDELS fields, where redshift accuracy from future surveys will rely only on the presence of a feature like the 4000\AA/Balmer breaks or the presence of emission lines within the grism spectra.

arXiv:1903.08714v1 [pdf, other]
The Astrophysical Multimessenger Observatory Network (AMON)
Comments: 11 pages, 2 figures, 4 tables

The Astrophysical Multimessenger Observatory Network (AMON) has been built with the purpose of enabling near real-time coincidence searches between different observatories and telescopes. Its mission is to evoke, exploit and explore multimessenger sources. AMON aims to promote the advancement of multimessenger astrophysics by allowing its participants to study the most energetic phenomena in the universe and to help answer some of the outstanding enigmas in astrophysics, fundamental physics, and cosmology. The main strength of AMON is its ability to combine and analyze sub-threshold data from different facilities. These data cannot generally be used standalone to identify astrophysical sources. The analysis algorithms used in AMON will identify statistically significant coincidence candidates of multimessenger events, leading to the distribution of AMON alerts used by partner observatories for real-time follow-up to catch transient events. We present the science motivation, partner observatories, implementation and summary of the current status of the AMON project.

arXiv:1903.08724v1 [pdf, other]
Stellar populations in hosts of giant radio galaxies and their neighbouring galaxies
Comments: 20 pages, 9 figures, to be publish in A&A

Context: Giant radio galaxies (with projected linear size of radio structure larger than 0.7 Mpc) are very rare and unusual objects. Only $\sim$5% of extended radio sources reach such sizes. Understanding of the processes responsible for their large sizes is crucial to further our knowledge about the radio source's evolution. Aims: We check the hypothesis that giants become extremely large due to the specific history of their host galaxy formation, as well as in the context of the cluster or group of galaxies where they evolve. Therefore we study the star formation histories in their host galaxies and in galaxies located in their neighbourhood. Methods: We studied 41 giant-size radio galaxies as well as galaxies located within a radius of 5 Mpc around giants to verify whether the external conditions of the intergalactic medium somehow influence the internal evolution of galaxies in the group/cluster. We compared the results with a control sample of smaller-sized Fanaroff--Riley type II radio galaxies and their neighbouring galaxies. We fit stellar continua in all galaxy spectra using the spectral synthesis code STARLIGHT and provide statistical analysis of the results. Results: We find that hosts of giant radio galaxies have a larger amount of intermediate age stellar populations compared with smaller-sized FRII radio sources. The same result is also visible when we compare neighbouring galaxies located up to 1.5 Mpc around giants and FRIIs. This may be evidence that star formation in groups with giants was triggered due to global processes occurring in the ambient intergalactic medium. These processes may also contribute to mechanisms responsible for the extremely large sizes of giants.

arXiv:1903.08733v1 [pdf, other]
OGLE-2018-BLG-0022: A Nearby M-dwarf Binary
Comments: Accepted by AJ. 23 pages, 8 figures

We report observations of the binary microlensing event OGLE-2018-BLG-0022, provided by the ROME/REA Survey, which indicate that the lens is a low-mass binary star consisting of M3 (0.375+/-0.020 Msun) and M7 (0.098+/-0.005 Msun) components. The lens is unusually close, at 0.998+/-0.047 kpc, compared with the majority of microlensing events, and despite its intrinsically low luminosity, it is likely that AO observations in the near future will be able to provide an independent confirmation of the lens masses.

arXiv:1903.08744v1 [pdf, other]
The Unexpected Spectrum of the Innermost Ejecta of the Red Hypergiant VY CMa
Comments: To appear in the Astrophysical Journal

HST/STIS spectra of the small clumps and filaments closest to the central star in VY CMa reveal that the very strong K I emission and TiO and VO molecular emission, long thought to form in a dusty circumstellar shell, actually originate in a few small clumps 100's of AU from the star. The K I lines are 10 to 20 times stronger in these nearest ejecta than on the star. The observations also confirm VO as a circumstellar molecule. In this letter we discuss the spectra of the features, their motions and ages, and the identification of the molecular emission. The strength of the atomic and molecular features in the small clumps present an astrophysical problem for the excitation process. We show that the clumps must have a nearly clear line of sight to the star's radiation.

arXiv:1903.08750v1 [pdf, other]
Coherent transition radiation from the geomagnetically-induced current in cosmic-ray air showers: Implications for the anomalous events observed by ANITA
Comments: No comment found

We show that coherent transition radiation (CTR) from the electrically-neutral transverse geomagnetic current (CTR-GM) has to be included in the radio emission models to understand the radio emission from a high-energy cosmic-ray air shower traversing a dielectric boundary. We demonstrate that for zenith angles less than roughly 70 degrees, combined with high surface elevation the inclusion of CTR-GM can significantly alter the emitted electric field. As such CTR-GM might provide a natural, standard model, explanation to the recent "anomalous" events observed by the ANITA detector.

arXiv:1903.08751v1 [pdf, other]
Plasma 2020 - Intracluster Medium Plasmas
Comments: 5 pages, 2 figures, submitted for the 2020 Decadal Assessment of Plasma Science

Galaxy clusters are the largest and most massive bound objects resulting from cosmic hierarchical structure formation. Baryons account for somewhat more than 10% of that mass, with roughly 90% of the baryonic matter distributed throughout the clusters as hot ($T>1$ keV), high-$\beta$, very weakly collisional plasma; the so-called "intracluster medium" (ICM). Cluster mergers, close gravitational encounters and accretion, along with violent feedback from galaxies and relativistic jets from active galactic nuclei, drive winds, gravity waves, turbulence and shocks within the ICM. Those dynamics, in turn, generate cluster-scale magnetic fields and accelerate and mediate the transport of high-energy charged particles. Kinetic-scale, collective plasma processes define the basic character and fundamental signatures of these ICM phenomena, which are observed primarily by X-ray and radio astronomers.

arXiv:1903.08753v1 [pdf, other]
Astro2020 Science White Paper: Triggered High-Priority Observations of Dynamic Solar System Phenomena
Comments: Astro2020 white paper

Unexpected dynamic phenomena have surprised solar system observers in the past and have led to important discoveries about solar system workings. Observations at the initial stages of these events provide crucial information on the physical processes at work. We advocate for long-term/permanent programs on ground-based and space-based telescopes of all sizes - including Extremely Large Telescopes (ELTs) - to conduct observations of high-priority dynamic phenomena, based on a predefined set of triggering conditions. These programs will ensure that the best initial dataset of the triggering event are taken; separate additional observing programs will be required to study the temporal evolution of these phenomena. While not a comprehensive list, the following are notional examples of phenomena that are rare, that cannot be anticipated, and that provide high-impact advances to our understandings of planetary processes. Examples include: new cryovolcanic eruptions or plumes on ocean worlds; impacts on Jupiter, Saturn, Uranus, or Neptune; extreme eruptions on Io; convective superstorms on Saturn, Uranus, or Neptune; collisions within the asteroid belt or other small-body populations; discovery of an interstellar object passing through our solar system (e.g. 'Oumuamua); and responses of planetary atmospheres to major solar flares or coronal mass ejections.

arXiv:1903.08757v1 [pdf, other]
Studying Magnetic Fields in Star Formation and the Turbulent Interstellar Medium
Comments: Submitted to the Astro2020 Decadal Survey (with a few updated citations)

Understanding the physics of how stars form is a highly-prioritized goal of modern Astrophysics, in part because star formation is linked to both galactic dynamics on large scales and to the formation of planets on small scales. It is well-known that stars form from the gravitational collapse of molecular clouds, which are in turn formed out of the turbulent interstellar medium. Star formation is highly inefficient, with one of the likely culprits being the regulation against gravitational collapse provided by magnetic fields. Measurement of the polarized emission from interstellar dust grains, which are partially aligned with the magnetic field, provides a key tool for understanding the role these fields play in the star formation process. Over the past decade, much progress has been made by the most recent generation of polarimeters operating over a range of wavelengths (from the far-infrared through the millimeter part of the spectrum) and over a range of angular resolutions (from less than an arcsecond through fractions of a degree). Future developments in instrument sensitivity for ground-based, airborne, and space-borne polarimeters operating over range of spatial scales are critical for enabling revolutionary steps forward in our understanding of the magnetized turbulence from which stars are formed.

arXiv:1903.08769v1 [pdf, other]
An analytical model of radial dust trapping in protoplanetary disks
Comments: No comment found

We study dust concentration in axisymmetric gas rings in protoplanetary disks. Given the gas surface density, we derived an analytical total dust surface density by taking into account the differential concentration of all the grain sizes. This model allows us to predict the local dust-to-gas mass ratio and the slope of the particle size distribution, as a function of radius. We test this analytical model comparing it with a 3D magneto-hydrodynamical simulation of dust evolution in an accretion disk. The model is also applied to the disk around HD 169142. By fitting the disk continuum observations simultaneously at $\lambda = 0.87$, 1.3, 3.0 mm, we obtain a global dust-to-gas mass ratio $\epsilon_{\rm global} = 1.05 \times 10^{-2}$ and a viscosity coefficient $\alpha = 1.35 \times 10^{-2}$. This model can be easily implemented in numerical simulations of accretion disks.

arXiv:1903.08777v1 [pdf, other]
The Disk Gas Mass and the Far-IR Revolution
Comments: Science white paper submitted to the Astro2020 Decadal Survey

The gaseous mass of protoplanetary disks is a fundamental quantity in planet formation. The presence of gas is necessary to assemble planetesimals, it determines timescales of giant planet birth, and it is an unknown factor for a wide range of properties of planet formation, from chemical abundances (X/H) to the mass efficiency of planet formation. The gas mass obtained from traditional tracers, such as dust thermal continuum and CO isotopologues, are now known to have significant (1 - 2 orders of magnitude) discrepancies. Emission from the isotopologue of H2, hydrogen deuteride (HD), offers an alternative measurement of the disk gas mass. Of all of the regions of the spectrum, the far-infrared stands out in that orders of magnitude gains in sensitivity can be gleaned by cooling a large aperture telescope to 8 K. Such a facility can open up a vast new area of the spectrum to exploration. One of the primary benefits of this far-infrared revolution would be the ability to survey hundreds of planet-forming disks in HD emission to derive their gaseous masses. For the first time, we will have statistics on the gas mass as a function of evolution, tracing birth to dispersal as a function of stellar spectral type. These measurements have broad implications for our understanding of the time scale during which gas is available to form giant planets, the dynamical evolution of the seeds of terrestrial worlds, and the resulting chemical composition of pre-planetary embryos carrying the elements needed for life. Measurements of the ground-state line of HD requires a space-based observatory operating in the far-infrared at 112 microns.

arXiv:1903.08790v1 [pdf, other]
Constrain the Rastall parameters in static spacetimes with galaxy-sclale strong gravitational lensing
Comments: 5 pages, 1 figure

Recently, Rastall gravity is undergoing a significant surge in popularity. We naturally obtain a power-law total mass-density profile for the inner regions (within several effective radius) of early-type galaxies (ETGs) from the space-time structures which are described by the static spherically-symmetric solutions of Rastall gravity under the assumption of the perfect fluid matter. We find that in the inner region of ETGs, the Rastall dimensionless parameter $\beta=\kappa\lambda$ determines the mass distribution. We then use 118 galaxy-galaxy strong gravitational lensing systems to constrain the Rastall dimensionless parameter $\beta$. We find that the mean value of $\beta$ for total 118 ETGs is $\beta=0.163\pm0.001$(68\% CL) with a minor intrinsic scatter of $\delta=0.020\pm 0.001$. Our work observationally illustrates the physical meaning of theRastall dimensionless parameter in galaxy scale. From the Newtonian approximation of Rastall gravity, we also find that an absolute isothermal mass distribution for ETGs is not allowed in the Rastall gravity framework.

arXiv:1903.08796v1 [pdf, other]
Evidence for a Young Stellar Population in Nearby Type 1 Active Galaxies
Comments: To appear in ApJ

To understand the physical origin of the close connection between supermassive black holes and their host galaxies, it is vital to investigate star formation properties in active galaxies. Using a large dataset of nearby type 1 active galactic nuclei (AGNs) with detailed structural decomposition based on high-resolution optical images obtained with the Hubble Space Telescope, we study the correlation between black hole mass and bulge luminosity and the (Kormendy) relation between bulge effective radius and surface brightness. In both relations, the bulges of type 1 AGNs tend to be more luminous than those of inactive galaxies with the same black hole mass or the same bulge size. This suggests that the central regions of AGN host galaxies have characteristically lower mass-to-light ratios than inactive galaxies, most likely due to the presence of a younger stellar population in active systems. In addition, the degree of luminosity excess appears to be proportional to the accretion rate of the AGN, revealing a physical connection between stellar growth and black hole growth. Adopting a simple toy model for the increase of stellar mass and black hole mass, we show that the fraction of young stellar population flattens out toward high accretion rates, possibly reflecting the influence of AGN-driven feedback.

arXiv:1903.08798v1 [pdf, other]
Emulators for the non-linear matter power spectrum beyond $Λ$CDM
Comments: 12 pages, 10 figures. Data can be found at https://github.com/HAWinther/FofrFittingFunction

Accurate predictions for the non-linear matter power spectrum are needed to confront theory with observations in current and near future weak lensing and galaxy clustering surveys. We propose a computationally cheap method to create an emulator for modified gravity models by utilizing existing emulators for $\Lambda$CDM. Using a suite of $N$-body simulations we construct a fitting function for the enhancement of both the linear and non-linear matter power spectrum in the commonly studied Hu-Sawicki $f(R)$ gravity model valid for wave-numbers $k \lesssim 5-10\, h\text{Mpc}^{-1}$ and redshifts $z \lesssim 3$. We show that the cosmology dependence of this enhancement is relatively weak so that our fit, using simulations coming from only one cosmology, can be used to get accurate predictions for other cosmological parameters. We also show that the cosmology dependence can, if needed, be included by using linear theory, approximate $N$-body simulations (such as COLA) and semi-analytical tools like the halo model. Our final fit can easily be combined with any emulator or semi-analytical models for the non-linear $\Lambda$CDM power spectrum to accurately, and quickly, produce a non-linear power spectrum for this particular modified gravity model. The method we use can be applied to fairly cheaply construct an emulator for other modified gravity models. As an application of our fitting formula we use it to compute Fisher-forecasts for how well galaxy clustering and weak lensing in a Euclid-like survey will be at constraining modifications of gravity.

arXiv:1903.08813v1 [pdf, other]
Stellar mass as a galaxy cluster mass proxy: application to the Dark Energy Survey redMaPPer clusters
Comments: 14 pages, 7 figures, submitted to MNRAS

We introduce a galaxy cluster mass observable, $\mu_\star$, based on the stellar masses of cluster members, and we present results for the Dark Energy Survey (DES) Year 1 observations. Stellar masses are computed using a Bayesian Model Averaging method, and are validated for DES data using simulations and COSMOS data. We show that $\mu_\star$ works as a promising mass proxy by comparing our predictions to X-ray measurements. We measure the X-ray temperature-$\mu_\star$ relation for a total of 150 clusters matched between the wide-field DES Year 1 redMaPPer catalogue, and Chandra and XMM archival observations, spanning the redshift range $0.1<z<0.7$. For a scaling relation which is linear in logarithmic space, we find a slope of $\alpha = 0.488\pm0.043$ and a scatter in the X-ray temperature at fixed $\mu_\star$ of $\sigma_{{\rm ln} T_X|\mu_\star}=0.266^{+0.019}_{-0.020}$ for the joint sample. By using the halo mass scaling relations of the X-ray temperature from the Weighing the Giants program, we further derive the $\mu_\star$-conditioned scatter in mass, finding $\sigma_{{\rm ln} M|\mu_\star}=0.26^{+ 0.15}_{- 0.10}$. These results are competitive with well-established cluster mass proxies used for cosmological analyses, showing that $\mu_\star$ can be used as a reliable and physically motivated mass proxy to derive cosmological constraints.

arXiv:1903.08825v1 [pdf, other]
Onset of giant planet migration before 4480 million years ago
Comments: Main text: 46564 characters with spaces/7549 words Tables: 3 Figures:7 References: 115

Immediately after their formation, the terrestrial planets experienced intense impact bombardment by comets, leftover planetesimals from primary accretion, and asteroids. This temporal interval in solar system evolution, termed late accretion, thermally and chemically modified solid planetary surfaces and may have impeded the emergence of life on the Hadean Earth. The sources and tempo of late accretion are, however, vague. Here, we present a timeline that relates variably retentive radiometric ages from asteroidal meteorites, to new dynamical models of late accretion that invokes giant planet migration. Reconciliation of the geochronological data with dynamical models shows that giant planet migration immediately leads to an intense 30 Myr influx of comets to the entire solar system. The absence of whole-sale crustal reset ages after 4450 Ma for the most resilient chronometers from Earth, Moon, Mars, Vesta and various meteorite parent bodies confines the onset of giant planet migration to no later than ca. 4480 Ma. Waning impacts from planetesimals, asteroids (and a minor cometary component) continue to strike the inner planets through a protracted monotonic decline in impactor flux; this is in agreement with predictions from crater chronology. Amended global 3-D thermal analytical bombardment models derived from our new impact mass-production functions show that persistent niches for prebiotic chemistry on the early Hadean Earth could endure late accretion for at least the last 4400 Myr.

arXiv:1903.08830v1 [pdf, other]
The Blueshift Of Civ Broad Emission Line In Qsos
Comments: 18 pages, 8 figures, Accepted for publication in AJ

For the sample from Ge et al. of 87 low-$z$ Palomar--Green (PG) quasi-stellar objects (QSOs) and 130 high-$z$ QSOs ($0<z<5$) with $\hb$-based single-epoch supermassive black hole (SMBH) masses, we performed a uniform decomposition of the \civ\ $\lambda$1549 broad-line profile. Based on the rest frame defined by the \oiii $\lambda$5007 narrow emission line, a medium-strong positive correlation is found between the \civ\ blueshift and the luminosity at 5100\AA\ or the Eddington ratio \leddR. A medium-strong negative relationship is found between the \civ\ blueshift and \civ\ equivalent width. These results support the postulation where the radiation pressure may be the driver of \civ\ blueshift. There is a medium strong correlation between the mass ratio of \civ-based to $\hb$-based \mbh and the \civ\ blueshift, which indicates that the bias for \civ-based \mbh is affected by the \civ\ profile.

arXiv:1903.08832v1 [pdf, other]
EHT-HOPS pipeline for millimeter VLBI data reduction
Comments: No comment found

We present the design and implementation of an automated data calibration and reduction pipeline for very-long-baseline interferometric (VLBI) observations taken at millimeter wavelengths. These short radio-wavelengths provide the best imaging resolution available from ground-based VLBI networks such as the Event Horizon Telescope (EHT) and the Global Millimeter VLBI Array (GMVA), but require specialized processing due to the strong effects from atmospheric opacity and turbulence as well as the heterogeneous nature of existing global arrays. The pipeline builds upon a calibration suite (HOPS) originally designed for precision geodetic VLBI. To support the reduction of data for astronomical observations, we have developed an additional framework for global phase and amplitude calibration which provides output in a standard data format for astronomical imaging and analysis. We test the pipeline on observations taken at 3.5 mm (86 GHz) by the GMVA joined by the phased Atacama Large Millimeter/submillimeter Array in April 2017, and demonstrate the benefits from the specialized processing of high frequency VLBI data with respect to classical analysis techniques.

arXiv:1903.08838v1 [pdf, other]
3D non-LTE line formation of neutral carbon in the Sun
Comments: 14 pages, 8 figures, 2 tables; accepted for publication in A&A

Carbon abundances in late-type stars are important in a variety of astrophysical contexts. However C i lines, one of the main abundance diagnostics, are sensitive to departures from local thermodynamic equilibrium (LTE). We present a model atom for non-LTE analyses of C i lines, that uses a new, physically-motivated recipe for the rates of neutral hydrogen impact excitation. We analyse C i lines in the solar spectrum, employing a three-dimensional (3D) hydrodynamic model solar atmosphere and 3D non-LTE radiative transfer. We find negative non-LTE abundance corrections for C i lines in the solar photosphere, in accordance with previous studies, reaching up to around 0.1 dex in the disk-integrated flux. We also present the first fully consistent 3D non-LTE solar carbon abundance determination: we infer log $\epsilon_{\text{C}}$ = $8.44\pm0.02$, in good agreement with the current standard value. Our models reproduce the observed solar centre-to-limb variations of various C i lines, without any adjustments to the rates of neutral hydrogen impact excitation, suggesting that the proposed recipe may be a solution to the long-standing problem of how to reliably model inelastic collisions with neutral hydrogen in late-type stellar atmospheres.

arXiv:1903.08840v1 [pdf, other]
A Cold Stellar Stream in Pegasus
Comments: 9 pages, 7 figures, accepted to MNRAS

We report the serendipitous discovery of a stellar stream in the constellation Pegasus in the south Galactic hemisphere. The stellar stream was detected using the SDSS Data Release 14 by means of a matched filter in the color--magnitude diagram that is optimised for a stellar population that is 8 Gyr old with [Fe/H] = $-$0.46 dex, and located at heliocentric distance of 18 kpc. The candidate stream is faint (turnoff point at $r_0 \sim$ 19.6), sparse and barely visible in SDSS photometry. It is also detected in the (shallower) Pan-STARRs data. The residual stellar density in the $(u-g)_0$, $(g-r)_0$ color--color diagram gives the same estimate for the age and [Fe/H] of this stellar population. The stream is located at a Galactic coordinates $(l,b) = (79.4,-24.6)$ and extends over 9$^\circ$ (2.5 kpc), with a width of 112 pc. The narrow width suggests a globular cluster progenitor.

arXiv:1903.08842v1 [pdf, other]
Gravitational Production of Superheavy Dark Matter and Associated Cosmological Signatures
Comments: 33 pages, 6 Figures

We study the gravitational production of super-Hubble-mass dark matter in the very early universe. We first review the simplest scenario where dark matter is produced mainly during slow roll inflation. Then we move on to consider the cases where dark matter is produced during the transition period between inflation and the subsequent cosmological evolution. The limits of smooth and sudden transitions are studied, respectively. The relic abundances and the cosmological collider signals are calculated.

arXiv:1903.08848v1 [pdf, other]
Exploring neutrino mass and mass hierarchy in interacting dark energy models
Comments: 9 pages, 3 figures

We investigate how the dark energy properties impact the constraints on the total neutrino mass in interacting dark energy (IDE) models. In this study, we focus on two typical interacting dynamical dark energy models, i.e., the I$w$CDM model and the IHDE model. To avoid the large-scale instability problem in IDE models, we apply the parameterized post-Friedmann (PPF) approach to calculate the perturbation of dark energy. We employ the Planck 2015 CMB temperature and polarization data, combined with low-redshift measurements on baryon acoustic oscillation distance scales, type Ia supernovae, and the Hubble constant, to constrain the cosmological parameters. We find that the dark energy properties could influence the constraint limits on the total neutrinos mass. Once dynamical dark energy is considered in the IDE models, the upper bounds of $\sum m_\nu$ will be changed. By considering the values of $\chi^2_{\rm min}$, we find that in these IDE models the NH case is slightly preferred over the IH case; for example, the difference of $\Delta\chi^2=2.720$ is given in the IHDE+$\sum m_\nu$ model. In addition, we also find that in the I$w$CDM+$\sum m_\nu$ model $\beta=0$ is consistent with current observational data inside the 1$\sigma$ range, and in the IHDE+$\sum m_\nu$ model $\beta>0$ is favored at more than the 2$\sigma$ level.

arXiv:1903.08867v1 [pdf, other]
Dynamics of electron beams in the inhomogeneous solar corona plasma
Comments: 10 figures, 19 pages

Dynamics of an spatially limited electron beam in the inhomogeneous solar corona plasma is considered in the framework of weak turbulence theory when the temperature of the beam significantly exceeds that of surrounding plasma. The numerical solution of kinetic equations manifests that generally the beam accompanied by Langmuir waves propagates as a beam-plasma structure with a decreasing velocity. Unlike the uniform plasma case the structure propagates with the energy losses in the form of Langmuir waves. The results obtained are compared with the results of observations of type III bursts. It is shown that the deceleration of type III sources can be explained by the corona inhomogeneity. The frequency drift rates of the type III sources are found in a good agreement with the numerical results of beam dynamics.

arXiv:1903.08884v1 [pdf, other]
The MASSIVE survey - XI. What drives the molecular gas properties of early-type galaxies
Comments: 19 pages, 12 figures, accepted by MNRAS

In this paper we study the molecular gas content of a representative sample of 67 of the most massive early-type galaxies in the local universe, drawn uniformly from the MASSIVE survey. We present new IRAM-30m telescope observations of 30 of these galaxies, allowing us to probe the molecular gas content of the entire sample to a fixed molecular-to-stellar mass fraction of 0.1%. The total detection rate in this representative sample is 25$^{+5.9}_{-4.4}$%, and by combining the MASSIVE and ATLAS$^{\rm 3D}$ molecular gas surveys we find a joint detection rate of 22.4$^{+2.4}_{-2.1}$%. This detection rate seems to be independent of galaxy mass, size, position on the fundamental plane, and local environment. We show here for the first time that true slow rotators can host molecular gas reservoirs, but the rate at which they do so is significantly lower than for fast-rotators. Objects with a higher velocity dispersion at fixed mass (a higher kinematic bulge fraction) are less likely to have detectable molecular gas, and where gas does exist, have lower molecular gas fractions. In addition, satellite galaxies in dense environments have $\approx$0.6 dex lower molecular gas-to-stellar mass ratios than isolated objects. In order to interpret these results we created a toy model, which we use to constrain the origin of the gas in these systems. We are able to derive an independent estimate of the gas-rich merger rate in the low-redshift universe. These gas rich mergers appear to dominate the supply of gas to ETGs, but stellar mass loss, hot halo cooling and transformation of spiral galaxies also play a secondary role.

arXiv:1903.08891v1 [pdf, other]
Discontinuities in numerical radiative transfer
Comments: No comment found

Observations and magnetohydrodynamic simulations of solar and stellar atmospheres reveal an intermittent behavior or steep gradients in physical parameters, such as magnetic field, temperature, and bulk velocities. The numerical solution of the stationary radiative transfer equation is particularly challenging in such situations, because standard numerical methods may perform very inefficiently in the absence of local smoothness. However, a rigorous investigation of the numerical treatment of the radiative transfer equation in discontinuous media is still lacking. The aim of this work is to expose the limitations of standard convergence analyses for this problem and to identify the relevant issues. Moreover, specific numerical tests are performed. These show that discontinuities in the atmospheric physical parameters effectively induce first-order discontinuities in the radiative transfer equation, reducing the accuracy of the solution and thwarting high-order convergence. In addition, a survey of the existing numerical schemes for discontinuous ordinary differential systems and interpolation techniques for discontinuous discrete data is given, evaluating their applicability to the radiative transfer problem.

arXiv:1903.08896v1 [pdf, other]
An energetic high-velocity compact cloud: CO$-$0.31+0.11
Comments: 11 pages, 7 figures, accepted for publication in PASJ

We have discovered an energetic high-velocity compact cloud CO$-$0.31+0.11 in the central molecular zone of our Galaxy. CO$-$0.31+0.11 is located at a projected distance of $\sim 45$ pc from the Galactic nucleus Sgr A$^*$. It is characterized by its compact spatial appearance ($d\simeq4$ pc), extremely broad velocity width ($\Delta V > 100$ km s$^{-1}$), and high CO $J$=3$-$2/$J$=1$-$0 intensity ratio. The total gas mass and kinetic energy are estimated as approximately $10^4$ $M_\odot$ and $10^{51}$ erg, respectively. Two expanding bubble-like structures are found in our HCN $J$=1$-$0 map obtained with the Nobeyama Radio Observatory 45 m telescope. In the longitude--velocity maps, CO$-$0.31+0.11 exhibits an asymmetric V-shape. This kinematical structure can be well fitted by Keplerian motion on an eccentric orbit around a point mass of $2\times 10^5$ $M_\odot$. The enhanced CO $J$=3$-$2/$J$=1$-$0 ratio is possibly attributed to the tidal compression during the pericenter passage. The model suggests that a huge mass is packed within a radius of $r < 0.1$ pc. The huge mass, compactness and absence of luminous stellar counterparts may correspond to a signature of an intermediate-mass black hole (IMBH) inside. We propose a formation scenario of CO$-$0.31+0.11 in which a compact cloud has gravitationally interacted with an IMBH and a bipolar molecular outflow was driven by the past activity of the putative IMBH.

arXiv:1903.08913v1 [pdf, other]
Searching for the Evidence of Dynamical Dark Energy
Comments: EPJC accepted. 7 figures, 10 pages

In the statistical framework of model-independent Gaussian processes (GP), we search for the evidence of dynamical dark energy (DDE) using the "Joint Light-curve Analysis" (JLA) Type Ia supernovae (SNe Ia) sample, the 30 latest cosmic chronometer data points (H(z)), Planck's shift parameter from cosmic microwave background (CMB) anisotropies, the 156 latest HII galaxy measurements and 79 calibrated gamma-ray bursts (GRBs). We find that the joint constraint from JLA + H(z) + CMB + HII + GRB supports the global measurement of $H_0$ by Planck collaboration very much in the low redshift range $z\in[0, 0.76]$ at the $2\sigma$ confidence level (C.L.), gives a cosmological constant crossing (quintom-like) equation of state (EoS) of DE at the $2\sigma$ C.L. and implies that the evolution of the late-time Universe may be actually dominated by the DDE.

arXiv:1903.08924v1 [pdf, other]
LISA Pathfinder
Comments: Preprint of an article submitted for consideration in Lepton-Photon 2017 conference proceedings \copyright 2019 copyright World Scientific Publishing Company

Since the 2017 Nobel Prize in Physics was awarded for the observation of gravitational waves, it is fair to say that the epoch of gravitational wave astronomy (GWs) has begun. However, a number of interesting sources of GWs can only be observed from space. To demonstrate the feasibility of the Laser Interferometer Space Antenna (LISA), a future gravitational wave observatory in space, the LISA Pathfinder satellite was launched on December, 3rd 2015. Measurements of the spurious forces accelerating an otherwise free-falling test mass, and detailed investigations of the individual subsystems needed to achieve the free-fall, have been conducted throughout the mission. This overview article starts with the purpose and aim of the mission, explains satellite hardware and mission operations and ends with a summary of selected important results and an outlook towards LISA. From the LISA Pathfinder experience, we can conclude that the proposed LISA mission is feasible.

arXiv:1903.08930v1 [pdf, other]
Precise optical timing of PSR J1023+0038, the first millisecond pulsar detected with Aqueye+ in Asiago
Comments: 6 pages, 4 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society Letters

We report the first detection of an optical millisecond pulsar with the fast photon counter Aqueye+ in Asiago. This is an independent confirmation of the detection of millisecond pulsations from PSR J1023+0038 obtained with SiFAP at the Telescopio Nazionale Galileo. We observed the transitional millisecond pulsar PSR J1023+0038 with Aqueye+ mounted at the Copernicus telescope in January 2018. Highly significant pulsations were detected. The rotational period is in agreement with the value extrapolated from the X-ray ephemeris, while the time of passage at the ascending node is shifted by $11.55 \pm 0.08$ s from the value predicted using the orbital period from the X-rays. An independent optical timing solution is derived over a baseline of a few days, that has an accuracy of $\sim 0.007$ in pulse phase ($\sim 12$ $\mu$s in time). This level of precision is needed to derive an accurate coherent timing solution for the pulsar and to search for possible phase shifts between the optical and X-ray pulses using future simultaneous X-ray and optical observations.

arXiv:1903.08932v1 [pdf, other]
A homogeneous sample of 34 000 M7-M9.5 dwarfs brighter than $J$=17.5 with accurate spectral types
Comments: Accepted for publication in A&A. 8 pages, 7 figures, and 5 tables. Catalogue of M dwarfs available on CDS (link in paper)

The space density of late M dwarfs, subtypes M7-M9.5, is not well determined. We applied the photo-type method to $iz$ photometry from the Sloan Digital Sky Survey and $YJHK$ photometry from the UKIRT Infrared Deep Sky Survey, over an effective area of 3070 $deg^{2}$, to produce a new, bright $J$(Vega) < 17.5, homogeneous sample of 33 665 M7-M9.5 dwarfs. The typical S/N of each source summed over the six bands is > 100. Classifications are provided to the nearest half spectral subtype. Through a comparison with the classifications in the BOSS Ultracool Dwarfs (BUD) spectroscopic sample, the typing is shown to be accurately calibrated to the BUD classifications and the precision is better than 0.5 subtypes rms; i.e. the photo-type classifcations are as precise as good spectroscopic classifications. Sources with large $\chi^2$ > 20 include several catalogued late-type subdwarfs. The new sample of late M dwarfs is highly complete, but there is a bias in the classification of rare peculiar blue or red objects. For example, L subdwarfs are misclassified towards earlier types by approximately two spectral subtypes. We estimate that this bias only affects ~1% of the course. Therefore the sample is well suited to measure the luminsoity function and investigate the softening towards the Galactic plane of the exponential variation of density with height.

arXiv:1903.08963v1 [pdf, other]
New Neutron Star Equation of State with Quark-Hadron Crossover
Comments: 8 pages, 10 figures

We introduce an improved version of the zero temperature quark-hadron crossover equation of state, QHC19, which describes hadronic matter by the Togashi et al.~equation of state, and quark matter via the Nambu--Jona-Lasinio model with two phenomenological parameters, a short range universal repulsion between quarks, and an attractive diquark interaction, producing pairing of quarks. We describe the physical ranges of these parameters and find a maximum neutron star mass, 2.35 Msun. After a brief review of the construction of the quark-hadronic equation of state by a constrained interpolation between hadronic and quark regimes of dense matter, we delineate the resultant neutron star properties. These agree very well with the inferences of the LIGO/Virgo collaboration, from GW170817, of the pressure vs. baryon density, neutron star radii, and tidal deformabilities.

arXiv:1903.08972v1 [pdf, other]
The CO2-broadened H2O continuum in the 100-1500 cm-1 region. Measurements, predictions and empirical model
Comments: Accepted for publication in the Journal of Quantitative Spectroscopy & Radiative Transfer (JQSRT); 11 pages and 3 figures

Transmission spectra of H$_2$O+CO$_2$ mixtures have been recorded, at 296, 325 and 366 K, for various pressures and mixture compositions using two experimental setups. Their analysis enables to retrieve values of the 'continuum' absorption by the CO$_2$-broadened H$_2$O line wings between 100 and 1500 cm$^{-1}$. The results are in good agreement with those, around 1300 cm$^{-1}$, of the single previous experimental study available. Comparisons are also made with direct predictions based on line-shape correction factors $\chi$ calculated, almost thirty years ago, using a quasistatic approach and an input H$_2$O-CO$_2$ intermolecular potential. They show that this model quite nicely predicts, with slightly overestimated values, the continuum over a spectral range where it varies by more than three orders of magnitude. An empirical correction is proposed, based on the experimental data, which should be useful for radiative transfer and climate studies in CO$_2$ rich planetary atmospheres.

arXiv:1903.08976v1 [pdf, other]
Ambipolar diffusion in large Prandtl number turbulence
Comments: 8 pages, 8 figures, 1 table, submitted to NMRAS

We study the effects of ambipolar diffusion (AD) on hydromagnetic turbulence. We use the strong coupling approximation where the drift velocity between ions and neutrals is proportional to the Lorentz force. We consider the regime of large magnetic Prandtl number, relevant to the interstellar medium. We quantify the effects of AD on total and spectral kinetic and magnetic energies, the Ohmic and AD dissipation rates, the statistics of the magnetic field, the current density, and the linear polarization as measured by the rotationally invariant $E$ and $B$ mode polarizations. We show that the kurtosis of the magnetic field decreases with increasing AD. The $E$ mode polarization changes its skewness from positive values for small AD to negative ones for large AD. Even when AD is weak, changes in AD have a marked effect on the skewness and kurtosis of $E$, and only a weak effect on those of $B$. These results open the possibility of employing $E$ and $B$ mode polarization as diagnostic tools to characterizing turbulent properties of the interstellar medium.

arXiv:1903.08982v1 [pdf, other]
Magnetic Reconnection, Cosmic Ray Acceleration, and Gamma-Ray emission around Black Holes and Relativistic Jets
Comments: Invited Review at the International Conference on Black Holes as Cosmic Batteries: UHECRs and Multimessenger Astronomy - BHCB2018, 12-15 September, 2018, Foz du Iguazu, Brasil, in press in Procs. of Science. arXiv admin note: text overlap with arXiv:1608.03173

Particle acceleration by magnetic reconnection is now recognized as an important process in magnetically dominated regions of galactic and extragalactic black hole sources. This process helps to solve current puzzles specially related to the origin of the very high energy flare emission in these sources. In this review, we discuss this acceleration mechanism and show recent analytical studies and multidimensional numerical SRMHD and GRMHD (special and general relativistic magnetohydrodynamical) simulations with the injection of test particles, which help us to understand this process both in relativistic jets and coronal regions of these sources. The very high energy and neutrino emission resulting from the accelerated particles by reconnection is also discussed.

arXiv:1903.08986v1 [pdf, other]
"Auxiliary" Science with the WFIRST Microlensing Survey
Comments: 9 pages, 3 figures, submitted to the Astro2020 Science White Paper call. This white paper draws heavily from Chapter 2.5 of Spergel et al. 2015 (arXiv:1503.03757), which was written by the lead author of this white paper

The Wide Field Infrared Survey Telescope (WFIRST) will monitor $\sim 2$ deg$^2$ toward the Galactic bulge in a wide ($\sim 1-2~\mu$m) W149 filter at 15-minute cadence with exposure times of $\sim$50s for 6 seasons of 72 days each, for a total $\sim$41,000 exposures taken over $\sim$432 days, spread over the 5-year prime mission. This will be one of the deepest exposures of the sky ever taken, reaching a photon-noise photometric precision of 0.01 mag per exposure and collecting a total of $\sim 10^9$ photons over the course of the survey for a W149$_{\rm AB}\sim 21$ star. Of order $4 \times 10^7$ stars will be monitored with W149$_{\rm AB}$<21, and 10$^8$ stars with W145$_{\rm AB}$<23. The WFIRST microlensing survey will detect $\sim$54,000 microlensing events, of which roughly 1% ($\sim$500) will be due to isolated black holes, and $\sim$3% ($\sim$1600) will be due to isolated neutron stars. It will be sensitive to (effectively) isolated compact objects with masses as low as the mass of Pluto, thereby enabling a measurement of the compact object mass function over 10 orders of magnitude. Assuming photon-noise limited precision, it will detect $\sim 10^5$ transiting planets with sizes as small as $\sim 2~R_\oplus$, perform asteroseismology of $\sim 10^6$ giant stars, measure the proper motions to $\sim 0.3\%$ and parallaxes to $\sim 10\%$ for the $\sim 6 \times 10^6$ disk and bulge stars in the survey area, and directly detect $\sim 5 \times 10^3$ Trans-Neptunian objects (TNOs) with diameters down to $\sim 10$ km, as well as detect $\sim 10^3$ occulations of stars by TNOs during the survey. All of this science will completely serendipitous, i.e., it will not require modifications of the WFIRST optimal microlensing survey design. Allowing for some minor deviation from the optimal design, such as monitoring the Galactic center, would enable an even broader range of transformational science.

arXiv:1903.08993v1 [pdf, other]
Metal Abundances and Depletions in the Neutral Interstellar Medium of Galaxies: the Local Volume as a Laboratory
Comments: 7 pages, 3 figures, ASTRO2020 white paper

The comparison of chemical abundances in the neutral gas of galaxies to photospheric abundances of old and young stars, ionized gas abundances, and abundances in galactic halos can trace the chemical enrichment of the universe through cosmic times. In particular, our understanding of chemical enrichment through spectroscopic observations of damped Lyman alpha systems (DLAs) relies on corrections for depletion of metals from the gas to the dust phase. These corrections must be determined in the nearby universe, where both gas-phase abundances and photospheric abundances of young stars recently formed out of the interstellar medium can be measured. Multi-object high-resolution (R>50,000) ultraviolet (970-2400 A) and optical (300-600 nm) spectroscopy toward massive stars in local volume galaxies (D < 15 Mpc) covering a wide range of metallicities (a few % solar to solar) and morphological types will provide the abundance and depletion measurements needed to obtain a detailed and comprehensive characterization of the lifecycle of metals in neutral gas and dust in galaxies, thereby observationally addressing important questions about chemical enrichment and galaxy evolution.

arXiv:1903.09017v1 [pdf, other]
Surface evolution of the Anhur region on comet 67P from high-resolution OSIRIS images
Comments: 19 pages, 16 figures; accepted for publication in Astronomy and Astrophysics for the Rosetta 2 special number

The southern hemisphere of comet 67P/Churyumov-Gerasimenko (67P) became observable by the Rosetta mission in March 2015, a few months before cometary southern vernal equinox. The Anhur region in the southern part of the comet's larger lobe was found to be highly eroded, enriched in volatiles, and highly active. We analyze high-resolution images of the Anhur region pre- and post-perihelion acquired by the OSIRIS imaging system on board the Rosetta mission. The Narrow Angle Camera is particularly useful for studying the evolution in Anhur in terms of morphological changes and color variations.}{Radiance factor images processed by the OSIRIS pipeline were coregistered, reprojected onto the 3D shape model of the comet, and corrected for the illumination conditions. We find a number of morphological changes in the Anhur region that are related to formation of new scarps; removal of dust coatings; localized resurfacing in some areas, including boulders displacements; and vanishing structures, which implies localized mass loss that we estimate to be higher than 50 million kg. The strongest changes took place in and nearby the Anhur canyon-like structure, where significant dust cover was removed, an entire structure vanished, and many boulders were rearranged. All such changes are potentially associated with one of the most intense outbursts registered by Rosetta during its observations, which occurred one day before perihelion passage. Moreover, in the niche at the foot of a new observed scarp, we also see evidence of water ice exposure that persisted for at least six months. The abundance of water ice, evaluated from a linear mixing model, is relatively high (> 20%). Our results confirm that the Anhur region is volatile-rich and probably is the area on 67P with the most pristine exposures near perihelion.

arXiv:1903.09041v1 [pdf, other]
X-ray absorbing column densities of a complete sample of short Gamma Ray Bursts
Comments: 7 pages, 3 figures, 1 table. Accepted for publication on A&A

We update a flux-limited complete sample of Swift-based SGRBs (SBAT4, D'Avanzo et al. 2014), bringing it to 25 events and doubling its previous redshift range. We then evaluate the column densities of the events in the updated sample, in order to compare them with the NH distribution of LGRBs, using the sample BAT6ext (Arcodia et al. 2016). We rely on Monte Carlo simulations of the two populations and compare the computed NH distributions with a two sample Kolmogorov Smirnov (K-S) test. We then study how the K-S probability varies with respect to the redshift range we consider. We find that the K-S probability keeps decreasing as redshift increases until at z$\sim$1.8 the probability that short and long GRBs come from the same parent distribution drops below 1$\%$. This testifies for an observational difference among the two populations. This difference may be due to the presence of highly absorbed LGRBs above z$\sim$1.3, which have not been observed in the SGRB sample yet, although this may be due to our inability to detect them, or to the relatively small sample size.

arXiv:1903.09045v1 [pdf, other]
Design for the First Narrowband Filter for the Dark Energy Camera: Optimizing the LAGER Survey for z ~ 7 Galaxies
Comments: 12 pages, 12 figures, submitted to PASP

We present the design for the first narrowband filter NB964 for the Dark Energy Camera (DECam), which is operated on the 4m Blanco Telescope at the Cerro Tololo Inter-American Observatory. The NB964 filter profile is essentially defined by maximizing the power of searching for Lyman alpha emitting galaxies (LAEs) in the epoch of reionization, with the consideration of the night sky background in the near-infrared and the DECam quantum efficiency. The NB964 filter was manufactured by Materion in 2015. It has a central wavelength of 964.2 nm and a full width at half maximum (FWHM) of 9.2 nm. An NB964 survey named LAGER (Lyman Alpha Galaxies in the Epoch of Reionization) has been ongoing since December 2015. Here we report results of lab tests, on-site tests and observations with the NB964 filter. The excellent performances of this filter ensure that the LAGER project is able to detect LAEs at z~7 with a high efficiency.

arXiv:1903.09046v1 [pdf, other]
The Ly$α$ Luminosity Function and Cosmic Reionization at $z \sim$ 7.0: a Tale of Two LAGER Fields
Comments: 15 pages, 11 figures, submitted to ApJ

We present the largest-ever sample of 79 Ly$\alpha$ emitters (LAEs ) at $z\sim$ 7.0 selected in the COSMOS and CDFS fields of the LAGER project (the Lyman Alpha Galaxies in the Epoch of Reionization). Our newly amassed ultra deep narrowband exposure and deeper/wider broadband images have more than doubled the number of LAEs in COSMOS, and we have selected 30 LAEs in the second field CDFS. We detect two large scale LAE-overdense regions in the COSMOS that are likely protoclusters at the highest redshift to date. We perform injection and recovery simulations to derive the sample incompleteness. We show significant incompleteness comes from blending with foreground sources, which however has not been corrected in LAE luminosity functions in {the} literature. The bright end bump in the Ly$\alpha$ luminosity function in COSMOS is confirmed with 6 (2 newly selected) luminous LAEs (L$_{Ly\alpha}$ $>$ 10$^{43.3}$ erg s$^{-1}$). Interestingly, the bump is absent in CDFS, in which only one luminous LAE is detected. Meanwhile, the faint end luminosity functions from the two fields well agree with each other. The 6 luminous LAEs in COSMOS coincide with 2 LAE-overdense regions, while such regions are not seen in CDFS. The bright end luminosity function bump could be attributed to ionized bubbles in a patchy reionization. It appears associated with cosmic overdensities, thus supports an inside-out reionization topology at $z$ $\sim$ 7.0, i.e., the high density peaks were ionized earlier compared to the voids. An average neutral hydrogen fraction of $x_{HI}$ $\sim$ 0.2 - 0.4 is derived at $z\sim$ 7.0 based on the cosmic evolution of the Ly$\alpha$ luminosity function.

arXiv:1903.09047v1 [pdf, other]
Lyman Alpha Galaxies in the Epoch of Reionization (LAGER): Spectroscopic Confirmation of Two Redshift ~ 7.0 Galaxies
Comments: ApJ submitted

We spectroscopically confirmed two narrow-band selected redshift 7.0 Ly$\alpha$ galaxies and studied their restframe UV spectra. The Ly$\alpha$ and other UV nebular lines are very useful to confirm the galactic redshifts and diagnose the different mechanisms driving the ionizing emission. We observed two narrowband-selected $z$=7.0 Ly$\alpha$ candidates in the LAGER Chandra Deep Field South (CDFS) field with IMACS at Magellan telescope and confirmed they are Ly$\alpha$ emitters at $z$=6.924 and 6.931. In one galaxy, we also obtained deep NIR spectroscopy, which yields non-detections of the high-ionization UV nebular lines. We measured upper-limits of the ratios of CIV$\lambda$1548/Ly$\alpha$, HeII$\lambda$1640/Ly$\alpha$, OIII]$\lambda$1660/Ly$\alpha$, and CIII]$\lambda$1909/Ly$\alpha$ from the NIR spectra. These upper-limits imply that the ionizing emission in this galaxy is dominated by normal star formation instead of AGN.

arXiv:1903.09048v1 [pdf, other]
The Type II-P Supernova 2017eaw: from explosion to the nebular phase
Comments: 34 pages, 19 figures, 7 tables; accepted for publication in ApJ

The nearby SN 2017eaw is a Type II-P (''plateau') supernova showing early-time, moderate CSM interaction. We present a comprehensive study of this SN including the analysis of high-quality optical photometry and spectroscopy covering the very early epochs up to the nebular phase, as well as near-UV and near-infrared spectra, and early-time X-ray and radio data. The combined data of SNe 2017eaw and 2004et allow us to get an improved distance to the host galaxy, NGC 6946, as $D \sim 6.85$ $\pm 0.63$ Mpc; this fits in recent independent results on the distance of the host and disfavors the previously derived (30% shorter) distances based on SN 2004et. From modeling the nebular spectra and the quasi-bolometric light curve, we estimate the progenitor mass and some basic physical parameters for the explosion and the ejecta. Our results agree well with previous reports on a RSG progenitor star with a mass of $\sim15-16$ M$_\odot$. Our estimation on the pre-explosion mass-loss rate ($\dot{M} \sim3 \times 10^{-7} -$ $1\times 10^{-6} M_{\odot}$ yr$^{-1}$) agrees well with previous results based on the opacity of the dust shell enshrouding the progenitor, but it is orders of magnitude lower than previous estimates based on general light-curve modeling of Type II-P SNe. Combining late-time optical and mid-infrared data, a clear excess at 4.5 $\mu$m can be seen, supporting the previous statements on the (moderate) dust formation in the vicinity of SN 2017eaw.

arXiv:1903.09049v1 [pdf, other]
TARDIS Paper I: A Constrained Reconstruction Approach to Modeling the z~2.5 Cosmic Web Probed by Lyman-alpha Forest Tomography
Comments: 18 pages, 14 figures

Recent Lyman-$\alpha$ forest tomography measurements of the intergalactic medium (IGM) have revealed a wealth of cosmic structures at high redshift ($z\sim 2.5$). In this work, we present the Tomographic Absorption Reconstruction and Density Inference Scheme (TARDIS), a new chrono-cosmographic analysis tool for understanding the formation and evolution of these observed structures. We use maximum likelihood techniques with a fast non-linear gravitational model to reconstruct the initial density field of the observed regions. We find that TARDIS allows accurate reconstruction of smaller scale structures than standard Wiener filtering techniques. Applying this technique to mock Lyman-$\alpha$ forest data sets that simulate ongoing and future surveys such as CLAMATO, Subaru-PFS or the ELTs, we are able to infer the underlying matter density field at observed redshift and classify the cosmic web structures. We find good agreement with the underlying truth both in the characteristic eigenvalues and eigenvectors of the pseudo-deformation tensor, with the eigenvalues inferred from 30m-class telescopes correlated at $r=0.95$ relative to the truth. As an output of this method, we are able to further evolve the inferred structures to late time ($z=0$), and also track the trajectories of coeval $z=2.5$ galaxies to their $z=0$ cosmic web environments.

arXiv:1903.09053v1 [pdf, other]
The O star hinterland of the Galactic starburst, NGC 3603
Comments: 11 pages, with a 6-page table (Appendix B). Accepted by MNRAS, 21st March 2019

The very bright and compact massive young cluster, NGC 3603, has been cited as an example of a starburst in the Milky Way and compared with the much-studied R136/30 Doradus region in the Large Magellanic Cloud. Here we build on the discovery by Mohr-Smith et al. (2017) of a large number of reddened O stars around this cluster. We construct a list of 288 candidate O stars with proper motions, in a region of sky spanning 1.5x1.5 square degrees centered on NGC 3603, by cross-matching the Mohr-Smith et al. (2017) catalogue with Gaia DR2 (Gaia Collaboration et al. 2018). This provides the basis for a first comprehensive examination of the proper motions of these massive stars in the halo of NGC 3603, relative to the much better studied central region. We identify up to 11 likely O star ejections -- 8 of which would have been ejected between 0.60 and 0.95 Myr ago (supporting the age of c.1 Myr that has been attributed to the bright cluster centre). Seven candidate ejections are arranged in a partial ring to the south of the cluster core spanning radii of 9-18 arcmin (18-36 pc if the cluster is 7 kpc away). We also show that the cluster has a halo of a further 100 O stars extending to a radius of at least 5 arcmin, adding to the picture of NGC 3603 as a scaled down version of the R136/30 Dor region.

arXiv:1903.09064v1 [pdf, other]
Bayesian Model Selection with Future 21cm Observations of The Epoch of Reionisation
Comments: 19 pages, 15 figures

We apply Bayesian statistics to perform model selection on different reionisation scenarios via the Multinest algorithm. Initially, we recover the results shown by 21CMMC for the parameter estimation of 21cmFAST models. We proceed to test several toy models of the Epoch of Reionisation (EoR) defined in contrasting morphology and scale. We find that LOFAR observations are unlikely to allow model selection even with long integration times. HERA would require 61 dipoles to perform the same analysis in 1080 hours, and becomes comparable to the SKA with 217 dipoles. We find the SKA requires only 324 hours of observation to conclusively distinguish between our models. Once model selection is achievable, an analysis of observational priors is performed finding that neutral fraction checks at specific redshifts add little to no inference. We show the difficulties in model selection at the level of distinguishing fiducial parameters within a model or distinguishing galaxies with a constant versus power law mass-to-light ratio. Finally, we explore the use of the Savage-Dickey density ratio to show the redundancy of the parameter Rmfp within 21cmFAST.

arXiv:1903.09068v1 [pdf, other]
Bulge plus disc and Sérsic decomposition catalogues for 16,908 galaxies in the SDSS Stripe 82 co-adds: A detailed study of the $ugriz$ structural measurements
Comments: 27 pages, 14 figures. MNRAS accepted. Our catalogs are available in TXT and SQL formats at http://orca.phys.uvic.ca/~cbottrel/share/Stripe82/Catalogs/

Quantitative characterization of galaxy morphology is vital in enabling comparison of observations to predictions from galaxy formation theory. However, without significant overlap between the observational footprints of deep and shallow galaxy surveys, the extent to which structural measurements for large galaxy samples are robust to image quality (e.g., depth, spatial resolution) cannot be established. Deep images from the Sloan Digital Sky Survey (SDSS) Stripe 82 co-adds provide a unique solution to this problem - offering $1.6-1.8$ magnitudes improvement in depth with respect to SDSS Legacy images. Having similar spatial resolution to Legacy, the co-adds make it possible to examine the sensitivity of parametric morphologies to depth alone. Using the Gim2D surface-brightness decomposition software, we provide public morphology catalogs for 16,908 galaxies in the Stripe 82 $ugriz$ co-adds. Our methods and selection are completely consistent with the Simard et al. (2011) and Mendel et al. (2014) photometric decompositions. We rigorously compare measurements in the deep and shallow images. We find no systematics in total magnitudes and sizes except for faint galaxies in the $u$-band and the brightest galaxies in each band. However, characterization of bulge-to-total fractions is significantly improved in the deep images. Furthermore, statistics used to determine whether single-S\'ersic or two-component (e.g., bulge+disc) models are required become more bimodal in the deep images. Lastly, we show that asymmetries are enhanced in the deep images and that the enhancement is positively correlated with the asymmetries measured in Legacy images.

arXiv:1903.09110v1 [pdf, other]
Mapping out the time-evolution of exoplanet processes
Comments: Astro2020 white paper

There are many competing theories and models describing the formation, migration and evolution of exoplanet systems. As both the precision with which we can characterize exoplanets and their host stars, and the number of systems for which we can make such a characterization increase, we begin to see pathways forward for validating these theories. In this white paper we identify predicted, observable correlations that are accessible in the near future, particularly trends in exoplanet populations, radii, orbits and atmospheres with host star age. By compiling a statistically significant sample of well-characterized exoplanets with precisely measured ages, we should be able to begin identifying the dominant processes governing the time-evolution of exoplanet systems.

arXiv:1903.09114v1 [pdf, other]
Inferring Explosion Properties from Type II-Plateau Supernova Light Curves
Comments: 26 pages, 29 figures. Submitted to ApJ. Comments welcome

We present advances in modeling Type IIP supernovae using \texttt{MESA} for evolution to shock breakout coupled with \texttt{STELLA} for generating light and radial velocity curves. Explosion models and synthetic light curves can be used to translate observable properties of supernovae (such as the luminosity at day 50 and the duration of the plateau, as well as the observable quantity $ET$) into families of explosions which produce the same light curve and velocities on the plateau. These predicted families of explosions provide a useful guide towards modeling observed SNe, and can constrain explosion properties when coupled with other observational or theoretical constraints. For an observed supernova with a measured ${\rm ^{56}Ni}$ mass, breaking the degeneracies within these families of explosions (ejecta mass, explosion energy, and progenitor radius) requires independent knowledge of one parameter. We expect the most common case to be a progenitor radius measurement for a nearby supernova. We show that ejecta velocities inferred from the Fe II 5169 \AA\ line measured during the majority of the plateau phase provide little additional information about explosion characteristics. Only during the initial shock cooling phase can photospheric velocity measurements potentially aid in unraveling light curve degeneracies.

arXiv:1903.09121v1 [pdf, other]
Quark-matter cores in neutron stars
Comments: 11 pages with 3 appendices, 13 figures, 3 EoS tables as ancillary files

We combine results from astrophysical observations and theoretical ab-initio calculations to investigate the presence of quark matter (QM) inside neutron stars (NSs). We find a clear qualitative change in the material properties of NS matter at energy densities comparable to those where quark-gluon plasma is created in heavy-ion collisions. In the low-density phase, the system has characteristics closely resembling those of hadronic matter, while the high-density phase can be clearly identified with nearly conformal QM. We show that QM is never present inside 1.44-M_sol NSs, but resides inside maximally massive NSs barring very specific and extreme conditions. Finally, for the heaviest observed NSs of approximately two solar masses, the fate of QM is found to strongly depend on the behavior of the speed of sound in the matter: if this quantity does not strongly violate the conformal limit c_s^2 < 1/3, these stars host sizable quark cores of at least five kilometers in radius.

arXiv:1903.09124v1 [pdf, other]
Tidal disruption event rates in galaxy merger remnants
Comments: Letter submitted to MNRAS

The rate of tidal disruption events (TDEs) depends sensitively on the stellar properties of the central galactic regions. Simulations show that galaxy mergers cause gas inflows that trigger nuclear starbursts that increase the central stellar density. Motivated by these numerical results, and by the observed over-representation of post-starburst galaxies among TDE hosts, we study the evolution of the TDE rate in high-resolution hydrodynamical simulations of a galaxy merger, in which we capture the evolution of the stellar density around the massive black holes (BHs) in the merging galaxies and in the final remnant. We post-process the simulation to obtain the TDE rate. At the second pericentre, a nuclear starburst enhances the stellar density around the BH in the least massive galaxy, leading to an enhancement of the TDE rate around the secondary BH, although the magnitude and the duration of the increase depend on the stochasticity of star formation on very small scales. The central stellar density around the primary BH remains instead fairly constant, and so is its TDE rate, until the two BHs bind and are surrounded by the same stellar environment. After the formation of the binary, the stellar density decreases, and so does the TDE rate.

arXiv:1903.09129v1 [pdf, other]
Another look at Black Hole Spins
Comments: An invited comment for Nature Astronomy

Do black holes rotate, and if yes, how fast? This question is fundamental and has broad implications, but still remains open. There are significant observational challenges in current spin determinations, and future facilities offer prospects for precision measurements.

arXiv:1903.09146v1 [pdf, other]
Two is a Crowd? Characterising the effect of photometric contamination on the extraction of the global asteroseismic parameter $ν_{\text{max}}$ in Red-Giant Binaries
Comments: No comment found

Theoretical scaling relations for solar-like oscillators and red giants are widely used to estimate fundamental stellar parameters. The accuracy and precision of these relations have often been questioned in the literature, with studies often utilising binarity for model-independent validation. However, it has not been tested if the photometric effects of binarity introduce a systematic effect on the extraction of the seismic properties of the pulsating component(s). In this paper, we present an estimation of the impact of a contaminating photometric signal with a distinct background profile on the global asteroseismic parameter $\nu_{\text{max}}$ through the analysis of synthetic red-giant binary light curves. We generate the pulsational and granulation parameters for single red giants with different masses, radii and effective temperatures from theoretical scaling relations and use them to simulate single red-giant light curves with the characteristics of Kepler long-cadence photometric data. These are subsequently blended together according to their light ratio to generate binary red-giant light curves of various configurations. We then perform a differential analysis to characterise the systematic effects of binarity on the extraction of $\nu_{\text{max}}$. We find that the $\nu_{\text{max}}$ extraction for red-giant power spectra featuring overlapping power excesses is unreliable if unconstrained priors are used. Outside of this scenario, we obtain results that are nearly identical to single-star case. We conclude that i) the photometric effects of binarity on the extraction of $\nu_{\text{max}}$ are largely negligible as long as the power excesses of the individual components do not overlap, and that ii) there is minimal advantage to using more than two super-Lorentzian components to model the granulation signal of a binary red-giant.

arXiv:1903.09147v1 [pdf, other]
Tidal disruptions by rotating black holes: effects of spin and impact parameter
Comments: 20 pages, 21 figures; submitted to MNRAS; comments welcome

We present the results of relativistic smoothed particle hydrodynamics simulations of tidal disruptions of stars by rotating supermassive black holes, for a wide range of impact parameters and black hole spins. For deep encounters, we find that: relativistic precession creates debris geometries impossible to obtain with the Newtonian equations; part of the fluid can be launched on plunging orbits, reducing the fallback rate and the mass of the resulting accretion disc; multiple squeezings and bounces at periapsis may generate distinctive X-ray signatures resulting from the associated shock breakout; disruptions can occur inside the marginally bound radius, if the angular momentum spread launches part of the debris on non-plunging orbits. Perhaps surprisingly, we also find relativistic effects important in partial disruptions, where the balance between self-gravity and tidal forces is so precarious that otherwise minor relativistic effects can have decisive consequences on the stellar fate. In between, where the star is fully disrupted but relativistic effects are mild, the difference resides in a gentler rise of the fallback rate, a later and smaller peak, and longer return times. However, relativistic precession always causes thicker debris streams, both in the bound part (speeding up circularization) and in the unbound part (accelerating and enhancing the production of separate transients). We discuss various properties of the disruption (compression at periapsis, shape and spread of the energy distribution) and potential observables (peak fallback rate, times of rise and decay, duration of super-Eddington fallback) as a function of the impact parameter and the black hole spin.