52 articles on Thursday, February 20


arXiv:2002.07812v1 [pdf, other]
Testing the fidelity of simulations of black hole -- galaxy co-evolution at z ~ 1.5 with observations
Comments: 10 pages, 5 figures. Submitted to ApJ. Comments are welcome

We examine the scaling relations between the mass of a supermassive black hole (SMBH) and its host galaxy properties at $1.2<z<1.7$ using both observational data and simulations. Recent measurements of 32 X-ray-selected broad-line Active Galactic Nucleus (AGNs) are compared with two independent state-of-the-art efforts, including the hydrodynamic simulation MassiveBlackII (MBII) and a semi-analytic model (SAM). After applying an observational selection function to the simulations, we find that both MBII and SAM agree well with the data, in terms of the central distribution. However, the dispersion in the mass ratio between black hole mass and stellar mass is significantly more consistent with the MBII prediction ($\sim0.3~$dex), than with the SAM ($\sim0.7~$dex), even when accounting for observational uncertainties. Hence, our observations can distinguish between the different recipes adopted in the models. The mass relations in the MBII are highly dependent on AGN feedback while the relations in the SAM are more sensitive to galaxy merger events triggering nuclear activity. Moreover, the intrinsic scatter in the mass ratio of our high-$z$ sample is comparable to that observed in the local sample, all but ruling out the proposed scenario the correlations are purely stochastic in nature arising from some sort of cosmic central limit theorem. Our results support the hypothesis of AGN feedback being responsible for a causal link between the SMBH and its host galaxy, resulting in a tight correlation between their respective masses.


arXiv:2002.07814v1 [pdf, other]
A deep view into the nucleus of the Sagittarius Dwarf Spheroidal Galaxy with MUSE. II. Kinematic characterization of the stellar populations
Comments: 21 Pages, 10 figures. Accepted for publication by ApJ

The Sagittarius dwarf spheroidal galaxy (Sgr dSph) is in an advanced stage of disruption but still hosts its nuclear star cluster (NSC), M54, at its center. In this paper, we present a detailed kinematic characterization of the three stellar populations present in M54: young metal-rich (YMR); intermediate-age metal-rich (IMR); and old metal-poor (OMP), based on the spectra of $\sim6500$ individual M54 member stars extracted from a large MUSE/VLT dataset. We find that the OMP population is slightly flattened with a low amount of rotation ($\sim0.8$ km s$^{-1}$) and with a velocity dispersion that follows a Plummer profile. The YMR population displays a high amount of rotation ($\sim5$ km s$^{-1}$) and a high degree of flattening, with a lower and flat velocity dispersion profile. The IMR population shows a high but flat velocity dispersion profile, with some degree of rotation ($\sim2$ km s$^{-1}$). We complement our MUSE data with information from \textit{Gaia DR2} and confirm that the stars from the OMP and YMR populations are comoving in 3D space, suggesting that they are dynamically bound. While dynamical evolutionary effects (e.g. energy equipartition) are able to explain the differences in velocity dispersion between the stellar populations, the strong differences in rotation indicate different formation paths for the populations, as supported by an $N$-body simulation tailored to emulate the YMR-OMP system. This study provides additional evidence for the M54 formation scenario proposed in our previous work, where this NSC formed via GC accretion (OMP) and in situ formation from gas accretion in a rotationally supported disc (YMR).


arXiv:2002.07815v1 [pdf, other]
Constraining the recent star formation history of galaxies : an Approximate Bayesian Computation approach
Comments: No comment found

[Abridged] Although galaxies are found to follow a tight relation between their star formation rate and stellar mass, they are expected to exhibit complex star formation histories (SFH), with short-term fluctuations. The goal of this pilot study is to present a method that will identify galaxies that are undergoing a strong variation of star formation activity in the last tens to hundreds Myr. In other words, the proposed method will determine whether a variation in the last few hundreds of Myr of the SFH is needed to properly model the SED rather than a smooth normal SFH. To do so, we analyze a sample of COSMOS galaxies using high signal-to-noise ratio broad band photometry. We apply Approximate Bayesian Computation, a state-of-the-art statistical method to perform model choice, associated to machine learning algorithms to provide the probability that a flexible SFH is preferred based on the observed flux density ratios of galaxies. We present the method and test it on a sample of simulated SEDs. The input information fed to the algorithm is a set of broadband UV to NIR (rest-frame) flux ratios for each galaxy. The method has an error rate of 21% in recovering the right SFH and is sensitive to SFR variations larger than 1 dex. A more traditional SED fitting method using CIGALE is tested to achieve the same goal, based on fits comparisons through Bayesian Information Criterion but the best error rate obtained is higher, 28%. We apply our new method to the COSMOS galaxies sample. The stellar mass distribution of galaxies with a strong to decisive evidence against the smooth delayed-$\tau$ SFH peaks at lower M* compared to galaxies where the smooth delayed-$\tau$ SFH is preferred. We discuss the fact that this result does not come from any bias due to our training. Finally, we argue that flexible SFHs are needed to be able to cover that largest SFR-M* parameter space possible.


arXiv:2002.07818v1 [pdf, other]
Project AMIGA: The Circumgalactic Medium of Andromeda
Comments: Submitted to the Astrophysical Journal. Comments welcome

Project AMIGA (Absorption Maps In the Gas of Andromeda) is a large ultraviolet Hubble Space Telescope program, which has assembled a sample of 43 QSOs that pierce the circumgalactic medium (CGM) of Andromeda (M31) from R=25 to 569 kpc (25 of them probing gas from 25 kpc to about the virial radius-Rvir = 300 kpc-of M31). Our large sample provides an unparalleled look at the physical conditions and distribution of metals in the CGM of a single galaxy using ions that probe a wide range of gas phases (Si II, Si III, Si IV, C II, C IV, and O VI, the latter being from the Far Ultraviolet Spectroscopic Explorer). We find that Si III and O VI have near unity covering factor maintained all the way out to 1.2Rvir and 1.9Rvir, respectively. We show that Si III is the dominant ion over Si II and Si IV at any R. While we do not find that the properties of the CGM of M31 depend strongly on the azimuth, we show that they change remarkably around 0.3-0.5Rvir, conveying that the inner regions of the CGM of M31 are more dynamic and have more complicated multi-phase gas-structures than at R>0.5Rvir. We estimate the metal mass of the CGM within Rvir as probed by Si II, Si III, and Si IV is 2x10^7 Msun and by O VI is >8x10^7 Msun, while the baryon mass of the 10^4-10^5.5 K gas is ~4x10^10 (Z/0.3 Zsun)^(-1) Msun within Rvir. We show that different zoom-in cosmological simulations of L* galaxies better reproduce the column density profile of O VI with R than Si III or the other studied ions. We find that observations of the M31 CGM and zoom-in simulations of L* galaxies have both lower ions showing higher column density dispersion and dependence on R than higher ions, indicating that the higher ionization structures are larger and/or more broadly distributed.


arXiv:2002.07820v1 [pdf, other]
The radio properties of HERGs with intermediate radio powers
Comments: 15 pages, 7 figures. Accepted for publication in Monthly Notices of the Royal Astronomical Society

In the past decade, high sensitivity radio surveys have revealed that the local radio AGN population is dominated by moderate-to-low power sources with emission that is compact on galaxy scales. High-excitation radio galaxies (HERGs) with intermediate radio powers (22.5 $<$ log(L$_{\rm 1.4GHz}$) $<$ 25.0 W Hz$^{-1}$) form an important sub-group of this population, since there is strong evidence that they also drive multi-phase outflows on the scales of galaxy bulges. Here, we present high-resolution VLA observations at 1.5, 4.5 and 7.5 GHz of a sample of 16 such HERGs in the local universe ($z<0.1$), conducted in order to investigate the morphology, extent and spectra of their radio emission in detail, down to sub-kpc scales. We find that the majority (56 per cent) have unresolved structures at the limiting angular resolution of the observations ($\sim$0.3"). Although similar in the compactness of their radio structures, these sources have steep radio spectra and host galaxy properties that distinguish them from local low-excitation radio galaxies (LERGs) that are unresolved on similar scales. The remaining sources exhibit extended radio structures with projected diameters $\sim$1.4$-$19.0 kpc and a variety of morphologies: three double-lobed; two large-scale diffuse; one jetted and 'S-shaped'; one undetermined. Only 19 per cent of the sample therefore exhibit the double-lobed/edge-brightened structures often associated with their counterparts at high and low radio powers: radio-powerful HERGs and Seyfert galaxies, respectively. Additional high-resolution observations are required to investigate this further, and to probe the $\lesssim$300 pc scales on which some Seyfert galaxies show extended structures.


arXiv:2002.07822v1 [pdf, other]
Towards Studying Hierarchical Assembly in Real Time: A Milky Way Progenitor Galaxy at z = 2.36 under the Microscope
Comments: Accepted to MNRAS

We use Hubble Space Telescope (HST) imaging and near-infrared spectroscopy from Keck/MOSFIRE to study the sub-structure around the progenitor of a Milky Way-mass galaxy in the Hubble Frontier Fields (HFF). Specifically, we study an $r_e = 40^{+70}_{-30}$pc, $M_{\star} \sim 10^{8.2} M_{\odot}$ rest-frame ultra-violet luminous "clump" at a projected distance of $\sim$100~pc from a $M_{\star} \sim 10^{9.8}$M$_{\odot}$ galaxy at $z = 2.36$ with a magnification $\mu = 5.21$. We measure the star formation history of the clump and galaxy by jointly modeling the broadband spectral energy distribution from HST photometry and H$\alpha$ from MOSFIRE spectroscopy. Given our inferred properties (e.g., mass, metallicity, dust) of the clump and galaxy, we explore scenarios in which the clump formed \emph{in-situ} (e.g., a star forming complex) or \emph{ex-situ} (e.g., a dwarf galaxy being accreted). If it formed \emph{in-situ}, we conclude that the clump is likely a single entity as opposed to a aggregation of smaller star clusters, making it one of the most dense star clusters cataloged. If it formed \emph{ex-situ}, then we are witnessing an accretion event with a 1:40 stellar mass ratio. However, our data alone are not informative enough to distinguish between \emph{in-situ} and \emph{ex-situ} scenarios to a high level of significance. We posit that the addition of high-fidelity metallicity information, such as [OIII]4363\AA, which can be detected at modest S/N with only a few hours of JWST/NIRSpec time, may be a powerful discriminant. We suggest that studying larger samples of moderately lensed sub-structures across cosmic time can provide unique insight into the hierarchical formation of galaxies like the Milky Way.


arXiv:2002.07825v1 [pdf, other]
Anisotropic infall in the outskirts of OmegaWINGS galaxy clusters
Comments: Accepted in MNRAS, 11 pages, 4 figures

We study the effects of the environment on galaxy quenching in the outskirts of clusters at $0.04 < z < 0.08$. We use a subsample of 14 WINGS and OmegaWINGS clusters that are linked to other groups/clusters by filaments and study separately galaxies located in two regions in the outskirts of these clusters according to whether they are located towards the filaments' directions or not. We also use samples of galaxies in clusters and field as comparison. Filamentary structures linking galaxy groups/clusters were identified over the Six Degree Field Galaxy Redshift Survey Data Release 3. We find a fraction of passive galaxies in the outskirts of clusters intermediate between that of the clusters and the field's. We find evidence of a more effective quenching in the direction of the filaments. We also analyse the abundance of post-starburst galaxies in the outskirts of clusters focusing our study on two extreme sets of galaxies according to their phase-space position: backsplash and true infallers. We find that up to $\sim70\%$ of post-starburst galaxies in the direction of filaments are likely backsplash, while this number drops to $\sim40\%$ in the isotropic infall region. The presence of this small fraction of galaxies in filaments that are falling into clusters for the first time and have been recently quenched, supports a scenario in which a significant number of filament galaxies have been quenched long time ago.


arXiv:2002.07828v1 [pdf, other]
The Environment of Lyman Break Analogues (ELBA) survey: Star-forming galaxies in small groups
Comments: 12 pages, 12 figures, submitted to MNRAS

The Environment of Lyman Break Analogues (ELBA) survey is an imaging survey of 33 $deg^{2}$ of the southern sky. The survey was observed in {\it u}, {\it g}, {\it r}, and {\it i} bands with the Dark Energy Camera (DECam) on the Blanco telescope. The main goal of this project is to investigate the environment of Lyman break analogues (LBAs), low-redshift (z $\sim $0.2) galaxies that are remarkably similar to typical star-forming galaxies at z $\sim$ 3. We explore whether the environment has any influence on the observed properties of these galaxies, providing valuable insight on the formation and evolution of galaxies over cosmic time. Using the Nearest Neighbour method, we measure the local density of each object ranging from small to large scales (clusters of galaxies). Comparing the environment around LBAs with that of the general galaxy population in the field, we conclude that LBAs, on average, populate denser regions at small scales ($\sim$ $1.5Mpc$), but are located in similar environment to other star-forming galaxies at larger scales ($\sim$ $3.0 Mpc$). This offers evidence that nearby encounters such as mergers may influence the star formation activity in LBAs, before infall onto larger galaxy clusters. We interpret this an indication of galaxy preprocessing, in agreement with theoretical expectations for galaxies at z $\sim$ 2 -3 where the gravitational interactions are more intense in early formation processes of this objects


arXiv:2002.07829v1 [pdf, other]
Let us bury the prehistoric $h$: arguments against using $h^{-1}{\rm Mpc}$ units in observational cosmology
Comments: 6 pages, 3 figures. Submitted to PRL

It is common to express cosmological measurements in units of $h^{-1}{\rm Mpc}$. Here, we review some of the complications that originate from this practice. A crucial problem caused by these units is related to the normalization of the matter power spectrum, which is commonly characterized in terms of the linear-theory rms mass fluctuation in spheres of radius $8\,h^{-1}{\rm Mpc}$, $\sigma_8$. This parameter does not correctly capture the impact of $h$ on the amplitude of density fluctuations. We show that the use of $\sigma_8$ has caused critical misconceptions for both the so-called $\sigma_8$ tension regarding the consistency between low-redshift probes and cosmic microwave background data, and the way in which growth-rate estimates inferred from redshift-space distortions are commonly expressed. We propose to abandon the use of $h^{-1}{\rm Mpc}$ units in cosmology and to characterize the amplitude of the matter power spectrum in terms of $\sigma_{12}$, defined as the mass fluctuation in spheres of radius $12\,{\rm Mpc}$, whose value is similar to the standard $\sigma_8$ for $h\sim 0.67$.


arXiv:2002.07831v1 [pdf, other]
Newly Improved Ionization Corrections for the Neutral Interstellar Medium: Enabling Accurate Abundance Determinations in Star-forming Galaxies throughout the Universe
Comments: 20 pages, 8 tables, 8 Figures, Accepted for Publication in ApJ

Studies measuring the chemical abundances of the neutral gas in star-forming galaxies (SFGs) require ionization correction factors (ICFs) to accurately measure their metal contents. In the work presented here we calculate newly improved ICFs for a sample of SFGs. These new corrections include both the contaminating ionized gas along the line of sight (ICF$_{\rm ionized}$) and unaccounted higher ionization stages in the neutral gas (ICF$_{\rm neutral}$). We make use of recently acquired spectroscopic observations taken with the Cosmic Origins Spectrograph (COS) on board Hubble to measure column densities for Fe II and Fe III. Using the Fe III/Fe II ratios as well as other physical properties (i.e. $\log$[L$_{\rm UV}$], $N$(H I), T, and $Z$) we generate ad-hoc photoionization models with CLOUDY to quantify the corrections required for each of the targets. We identify a luminosity threshold of $\log$[L$_{\rm UV}$]$\sim$ 40.75 erg s$^{-1}$ above which the ICF$_{\rm neutral}$ values for nitrogen are relatively higher (ICF$_{\rm neutral}=0.05$-0.7) than those for the rest of the elements (ICF$_{\rm neutral}\sim 0.01$). This behavior indicates that for the high UV luminosity objects, N II is found in non-negligible quantities in the neutral gas, making these ICF$_{\rm neutral}$ corrections critical for determining the true abundances in the interstellar medium. In addition, we calculate ICFs from a uniform grid of models covering a wide range of physical properties typically observed in studies of SFGs and extragalactic H II regions. We provide the community with tabulated ICF values for the neutral gas abundances measured from a variety of environments and applicable to chemical studies of the high redshift universe.


arXiv:2002.07847v1 [pdf, other]
The Solar wind prevents re-accretion of debris after Mercury's giant impact
Comments: 14 pages, 6 Figures, Accepted for publication in The Planetary Science Journal (AAS journals)

The planet Mercury possesses an anomalously large iron core, and a correspondingly high bulk density. Numerous hypotheses have been proposed in order to explain such a large iron content. A long-standing idea holds that Mercury once possessed a larger silicate mantle which was removed by a giant impact early in the the Solar system's history. A central problem with this idea has been that material ejected from Mercury is typically re-accreted onto the planet after a short (~Myr) timescale. Here, we show that the primordial Solar wind would have provided sufficient drag upon ejected debris to remove them from Mercury-crossing trajectories before re-impacting the planet's surface. Specifically, the young Sun likely possessed a stronger wind, fast rotation and strong magnetic field. Depending upon the time of the giant impact, the ram pressure associated with this wind would push particles outward into the Solar system, or inward toward the Sun, on sub-Myr timescales, depending upon the size of ejected debris. Accordingly, the giant impact hypothesis remains a viable pathway toward the removal of planetary mantles, both on Mercury and extrasolar planets, particularly those close to young stars with strong winds.


arXiv:2002.07850v1 [pdf, other]
No Massive Companion to the Coherent Radio-Emitting M Dwarf GJ 1151
Comments: No comment found

The recent detection of circularly polarized, long-duration (>8 hr) low-frequency (~150 MHz) radio emission from the M4.5 dwarf GJ 1151 has been interpreted as arising from a star-planet interaction via the electron cyclotron maser instability. The existence or parameters of the proposed planets have not been determined. Using 20 new HARPS-N observations, we put 99th-percentile upper limits on the mass of any close companion to GJ 1151 at Msini < 5.6 M earth. With no stellar, brown dwarf, or giant planet companion likely in a close orbit, our data are consistent with detected radio emission emerging from a magnetic interaction between a short-period terrestrial-mass planet and GJ 1151.


arXiv:2002.07852v1 [pdf, other]
A Mystery in Chamaeleon: Serendipitous Discovery of a Galactic Symbiotic Nova
Comments: Submitted to AJ, 19 pages, 9 figure

We present the serendipitous discovery of a low luminosity nova occurring in a symbiotic binary star system in the Milky Way. We lay out the extensive archival data alongside new follow-up observations related to the stellar object V$^*$ CN Cha in the constellation of Chamaeleon. The object had long period ($\sim\! 250\,$day), high amplitude ($\sim\! 3\,$mag) optical variability in its recent past, preceding an increase in optical brightness by $\sim\! 8\,$magnitudes and a persistence at this luminosity for about 3 years, followed by a period of $\sim\! 1.4\,{\rm mag}\,{\rm yr}^{-1}$ dimming. The object's current optical luminosity seems to be dominated by H$\alpha$ emission, which also exhibits blue-shifted absorption (a P-Cygni-like profile). After consideration of a number of theories to explain these myriad observations, we determine that V$^*$ CN Cha is most likely a symbiotic (an evolved star-white dwarf binary) system which has undergone a long-duration, low luminosity, nova. Interpreted in this way, the outburst in V$^*$ CN Cha is among the lowest luminosity novae ever observed.


arXiv:2002.07854v1 [pdf, other]
Detecting Pair-Instability Supernovae at z<5 with the James Webb Space Telescope
Comments: submitted to ApJ

Pair-instability supernovae (PISNe) are the ultimate cosmic lighthouses, capable of being observed at z<25 and revealing the properties of primordial stars at cosmic dawn. But it is now understood that the spectra and light curves of these events evolved with redshift as the universe became polluted with heavy elements because chemically enriched stars in this mass range typically lose most of their hydrogen envelopes and explode as bare helium cores. The light curves of such transients can be considerably dimmer in the near infrared (NIR) today than those of primordial PISNe of equal energy and progenitor mass. Here, we calculate detection rates for PISNe whose progenitors lost their outer layers to either line-driven winds or rotation at z<10, their detection limit in redshift for the James Webb Space Telescope (JWST). We find that JWST may be able to detect only Pop II (metal-poor) PISNe over the redshift range of z<4, but not their Pop III (metal-free) counterparts.


arXiv:2002.07894v1 [pdf, other]
Fragmentation modelling of the August 2019 impact on Jupiter
Comments: 10 pages, 8 figures, 2 tables, Accepted for publication in MNRAS

On 7th August 2019, an impact flash lasting $\sim1$s was observed on Jupiter. The video of this event was analysed to obtain the lightcurve and determine the energy release and initial mass. We find that the impactor released a total energy of $96-151$ kilotons of TNT, corresponding to an initial mass between $190-260$ metric tonnes with a diameter between $4-10$m. We developed a fragmentation model to simulate the atmospheric breakup of the object and reproduce the lightcurve. We model three different materials: cometary, stony and metallic at speeds of $60$, $65 $ and $70$ km/s to determine the material makeup of the impacting object. The slower cases are best fit by a strong, metallic object while the faster cases require a weaker material.


arXiv:2002.07921v1 [pdf, other]
MEM_GE: a new maximum entropy method for image reconstruction from solar X-ray visibilities
Comments: No comment found

Maximum Entropy is an image reconstruction method conceived to image a sparsely occupied field of view and therefore particularly appropriate to achieve super-resolution effects. Although widely used in image deconvolution, this method has been formulated in radio astronomy for the analysis of observations in the spatial frequency domain, and an Interactive Data Language (IDL) code has been implemented for image reconstruction from solar X-ray Fourier data. However, this code relies on a non-convex formulation of the constrained optimization problem addressed by the Maximum Entropy approach and this sometimes results in unreliable reconstructions characterized by unphysical shrinking effects. This paper introduces a new approach to Maximum Entropy based on the constrained minimization of a convex functional. In the case of observations recorded by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), the resulting code provides the same super-resolution effects of the previous algorithm, while working properly also when that code produces unphysical reconstructions. Results are also provided of testing the algorithm with synthetic data simulating observations of the Spectrometer/Telescope for Imaging X-rays (STIX) in Solar Orbiter. The new code is available in the {\em{HESSI}} folder of the Solar SoftWare (SSW)tree.


arXiv:2002.07938v1 [pdf, other]
A slow-down time-transformed symplectic integrator for solving the few-body problem
Comments: 14 pages, 13 figures, accepted to MNRAS

An accurate and efficient method dealing with the few-body dynamics is important for simulating collisional N-body systems like star clusters and to follow the formation and evolution of compact binaries. We describe such a method which combines the time-transformed explicit symplectic integrator (Preto & Tremaine 1999; Mikkola & Tanikawa 1999) and the slow-down method (Mikkola & Aarseth 1996). The former conserves the Hamiltonian and the angular momentum for a long-term evolution, while the latter significantly reduces the computational cost for a weakly perturbed binary. In this work, the Hamilton equations of this algorithm are analyzed in detail. We mathematically and numerically show that it can correctly reproduce the secular evolution like the orbit averaged method and also well conserve the angular momentum. For a weakly perturbed binary, the method is possible to provide a few order of magnitude faster performance than the classical algorithm. A publicly available code written in the c++ language, SDAR, is available on GitHub (https://github.com/lwang-astro/SDAR). It can be used either as a stand alone tool or a library to be plugged in other $N$-body codes. The high precision of the floating point to 62 digits is also supported.


arXiv:2002.07940v1 [pdf, other]
A unified framework for 21cm tomography sample generation and parameter inference with Progressively Growing GANs
Comments: 15 pages, 8+1 figures, accepted by MNRAS

Creating a database of 21cm brightness temperature signals from the Epoch of Reionisation (EoR) for an array of reionisation histories is a complex and computationally expensive task, given the range of astrophysical processes involved and the possibly high-dimensional parameter space that is to be probed. We utilise a specific type of neural network, a Progressively Growing Generative Adversarial Network (PGGAN), to produce realistic tomography images of the 21cm brightness temperature during the EoR, covering a continuous three-dimensional parameter space that models varying X-ray emissivity, Lyman band emissivity, and ratio between hard and soft X-rays. The GPU-trained network generates new samples at a resolution of $\sim 3'$ in a second (on a laptop CPU), and the resulting global 21cm signal, power spectrum, and pixel distribution function agree well with those of the training data, taken from the 21SSD catalogue \citep{Semelin2017}. Finally, we showcase how a trained PGGAN can be leveraged for the converse task of inferring parameters from 21cm tomography samples via Approximate Bayesian Computation.


arXiv:2002.07941v1 [pdf, other]
Asteroid Diameters and Albedos from NEOWISE Reactivation Mission Years Four and Five
Comments: Accepted for publication in the AAS Planetary Science Journal

The Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) spacecraft has been conducting a two-band thermal infrared survey to detect and characterize asteroids and comets since its reactivation in Dec 2013. Using the observations collected during the fourth and fifth years of the survey, our automated pipeline detected candidate moving objects which were verified and reported to the Minor Planet Center. Using these detections, we perform thermal modeling of each object from the near-Earth object and Main Belt asteroid populations to constrain their sizes. We present thermal model fits of asteroid diameters for 189 NEOs and 5831 MBAs detected during the fourth year of the survey, and 185 NEOs and 5776 MBAs from the fifth year. To date, the NEOWISE Reactivation survey has provided thermal model characterization for 957 unique NEOs. Including all phases of the original WISE survey brings the total to 1473 unique NEOs that have been characterized between 2010 and the present.


arXiv:2002.07979v1 [pdf, other]
Sympathetic eruptions of two filaments with an identifiable causal link observed by the Solar Dynamics Observatory
Comments: 20 pages, 7 figures, accepted for publication in ApJ

Filament eruptions occurring at different places within a relatively short time internal, but with a certain physical causal connection are usually known as sympathetic eruption. Studies on sympathetic eruptions are not uncommon. However, in the existed reports, the causal links between sympathetic eruptions remain rather speculative. In this work, we present detailed observations of a sympathetic filament eruption event, where an identifiable causal link between two eruptive filaments is observed. On 2015 November 15, two filaments (F1 in the north and F2 in the south) were located at the southwestern quadrant of solar disk. The main axes of them were almost parallel to each other. Around 22:20 UT, F1 began to erupt, forming two flare ribbons. The southwestern ribbon apparently moved to southwest and intruded southeast part of F2. This continuous intrusion caused F2's eventual eruption. Accompanying the eruption of F2, flare ribbons and post-flare loops appeared in northwest region of F2. Meanwhile, neither flare ribbons nor post-flare loops could be observed in southeastern area of F2. In addition, the nonlinear force-free field (NLFFF) extrapolations show that the magnetic fields above F2 in the southeast region are much weaker than that in the northwest region. These results imply that the overlying magnetic fields of F2 were not uniform. So we propose that the southwest ribbon formed by eruptive F1 invaded F2 from its southeast region with relatively weaker overlying magnetic fields in comparison with its northwest region, disturbing F2 and leading F2 to erupt eventually.


arXiv:2002.07991v1 [pdf, other]
Deep learning for intensity mapping observations: Component extraction
Comments: 5 pages, 3 figures, submitted to MNRAS

Line intensity mapping (LIM) is an emerging observational method to study the large-scale structure of the universe and its evolution. LIM does not resolve individual sources but probes the fluctuations of integrated line emissions. A serious limitation with LIM is that contributions of different emission lines from sources at different redshifts are all confused at an observed wavelength. We propose a deep learning application to solve this problem. We use conditional generative adversarial networks to extract designated information from LIM. We consider a simple case with two populations of emission line galaxies; H$\rm\alpha$ emitting galaxies at $z = 1.3$ are confused with [OIII] emitters at $z = 2.0$ in a single observed waveband at 1.5 $\rm\mu$m. Our networks trained with 30,000 mock observation maps are able to extract the total intensity and the spatial distribution of H$\rm\alpha$ emitting galaxies at $z = 1.3$. The intensity peaks, i.e. galaxy clusters, are successfully located with 61% precision. The precision increases to 83% when we combine the results of 5 networks. The mean intensity and the power spectrum are reconstructed with an accuracy of $\sim$10%. The extracted galaxy distributions at a wider range of redshift can be used for studies on cosmology and on galaxy formation and evolution.


arXiv:2002.07996v1 [pdf, other]
Obtaining magnetic field strength using differential measure approach and velocity channel maps
Comments: 30 pages, 10 figures, submitted to ApJ

We introduce two new ways of obtaining the strength of plane-of-sky (POS) magnetic field by simultaneous use of spectroscopic Doppler-shifted lines and the information on magnetic field direction. The latter can be obtained either through polarization measurements or using the velocity gradient technique. We show the advantages that our techniques have compared to the traditional Davis-Chandrasekhar-Fermi (DCF) technique of estimating magnetic field strength from observations. The first technique that we describe in detail employs structure functions of velocity centroids and structure functions of Stokes parameters. We provide analytical expressions for obtaining magnetic field strength from observational data. We successfully test our results using synthetic observations obtained with results of MHD turbulence simulations. We measure velocity and magnetic field fluctuations at small scales using two, three and four point structure functions and compare the performance of these tools. We show that, unlike the DCF, our technique is capable of providing the detailed distribution of POS magnetic field and it can measure magnetic field strength in the presence of both velocity and magnetic field distortions arising from external shear and self-gravity. The second technique applies the velocity gradient technique to velocity channel maps in order to obtain the Alfven Mach number and uses the amplitudes of the gradients to obtain the sonic Mach number. The ratio of these two Mach numbers provides the intensity of magnetic field in the region contributing to the emission in the channel map. We test the technique and discuss obtaining the 3D distribution of POS galactic Magnetic field with it. We discuss the application of the second technique to synchrotron data.


arXiv:2002.08001v1 [pdf, other]
Physical Parameters of Late-type Contact Binaries in the Northern Catalina Sky Survey
Comments: 2o pages, 10 figures, 2 tables. Accepted for publication in ApJS

We present the physical parameters of 2335 late-type contact binary (CB) systems extracted from the Catalina Sky Survey (CSS). Our sample was selected from the CSS Data Release 1 by strictly limiting the prevailing temperature uncertainties and light-curve fitting residuals, allowing us to almost eliminate any possible contaminants. We developed an automatic Wilson--Devinney-type code to derive the relative properties of CBs based on their light-curve morphology. By adopting the distances derived from CB (orbital) period--luminosity relations (PLRs), combined with the well-defined mass--luminosity relation for the systems' primary stars and assuming solar metallicity, we calculated the objects' masses, radii, and luminosities. Our sample of fully eclipsing CBs contains 1530 W-, 710 A-, and 95 B-type CBs. A comparison with literature data and with the results from different surveys confirms the accuracy and coherence of our measurements. The period distributions of the various CB subtypes are different, hinting at a possible evolutionary sequence. W-type CBs are clearly located in a strip in the total mass versus mass ratio plane, while A-type CBs may exhibit a slightly different dependence. There are no significant differences among the PLRs of A- and W-type CBs, but the PLR zero points are affected by their mass ratios and fill-out factors. Determination of zero-point differences for different types of CBs may help us improve the accuracy of the resulting PLRs. We demonstrate that automated approaches to deriving CB properties could be a powerful tool for application to the much larger CB samples expected to result from future surveys.


arXiv:2002.08011v1 [pdf, other]
Masses of double neutron star mergers
Comments: 5+2 pages, 3 figures, 3 tables, submitted to A&A

Aims. The mass discrepancy between the observed population of double neutron star binaries by radio pulsar observations and gravitational-wave observation requires an explanation. Methods. Binary population synthesis calculations are performed, and their results are compared with the radio and the gravitational-wave observations simultaneously. Results. Simulations of binary evolution are used to link different observations of double neutron star binaries with each other. The progenitor of GW190425 is investigated in more detail. A distribution of masses and merger times of the possible progenitors is presented. Conclusions. A mass discrepancy between the radio pulsars in the Milky Way with another neutron star companion and the inferred masses from gravitational-wave observations of those kind of merging systems is naturally found in binary evolution.


arXiv:2002.08017v1 [pdf, other]
Gaseous dynamical friction under radiative feedback: do intermediate-mass black holes speed up or down?
Comments: 12 pages, 11 figures, submitted to MNRAS

Coalescence of intermediate-mass black holes (IMBHs) as a result of the migration toward galactic centers via dynamical friction may contribute to the formation of supermassive BHs. Here we reinvestigate the gaseous dynamical friction, which was claimed to be inefficient with radiative feedback from BHs in literature, by performing 3D radiation-hydrodynamics simulations that solve the flow structure in the vicinity of BHs. We consider a $10^4~M_\odot$ BH moving at the velocity $V_{\rm flow}$ through the homogeneous medium with metallicity $Z$ in the range of $0-0.1~Z_\odot$ and density $n_{\infty}$. We show that, if $n_{\infty} \lesssim 10^{6}~{\rm cm^{-3}}$ and $V_{\rm flow} \lesssim 60~{\rm km~s^{-1}}$, the BH is accelerated forward because of the gravitational pull from a dense shell ahead of an ionized bubble around the BH, regardless of the value of $Z$. If $n_{\infty} \gtrsim 10^{6}~{\rm cm^{-3}}$, however, our simulation shows the opposite result. The ionized bubble and associating shell temporarily appear, but immediately go downstream with significant ram pressure of the flow. They eventually converge into a massive downstream wake, which gravitationally drags the BH backward. The BH decelerates over the timescale of $\sim 0.01$~Myr, much shorter than the dynamical timescale in galactic disks. Our results suggest that IMBHs that encounter the dense clouds rapidly migrate toward galactic centers, where they possibly coalescence with others.


arXiv:2002.08023v1 [pdf, other]
Dust Destruction by Charging: A Possible Origin of Grey Extinction Curves of Active Galactic Nuclei
Comments: 8 pages, 6 Figures; Accepted for publication in ApJ

Observed extinction curves of active galactic nuclei (AGNs) are significantly different from those observed in the Milky Way. The observations require preferential removal of small grains at the AGN environment; however, the physics for this remains unclear. In this paper, we propose that dust destruction by charging, or Coulomb explosion, may be responsible for AGN extinction curves. Harsh AGN radiation makes a dust grain highly charged through photoelectric emission, and grain fission via the Coulomb explosion occurs when the electrostatic tensile stress of a charge grain exceeds its tensile strength. We show that the Coulomb explosion can preferentially remove both small silicate and graphite grains and successfully reproduce both flat extinction curves and the absence of 2175\AA~bump.


arXiv:2002.08028v1 [pdf, other]
Variability and the size-luminosity relation of the intermediate mass AGN in NGC 4395
Comments: 18 pages, 10 figures, submitted to ApJ and edited based off of the reviewer's suggestions

We present the variability study of the lowest-luminosity Seyfert 1 galaxy NGC 4395 based on the photometric monitoring campaigns in 2017 and 2018. Using 22 ground-based and space telescopes, we monitored NGC 4395 with a $\sim$5 minute cadence during a period of 10 days and obtained light curves in the UV, V, J, H, and K/Ks bands as well as the H$\alpha$ narrow-band. The RMS variability is $\sim$0.13 mag on \emph{Swift}-UVM2 and V filter light curves, decreasing down to $\sim$0.01 mag on K filter. After correcting for continuum contribution to the H$\alpha$ narrow-band, we measured the time lag of the H$\alpha$ emission line with respect to the V-band continuum as ${55}^{+27}_{-31}$ to ${122}^{+33}_{-67}$ min. in 2017 and ${49}^{+15}_{-14}$ to ${83}^{+13}_{-14}$ min. in 2018, depending on the assumption on the continuum variability amplitude in the H$\alpha$ narrow-band. We obtained no reliable measurements for the continuum-to-continuum lag between UV and V bands and among near-IR bands, due to the large flux uncertainty of UV observations and the limited time baseline. We determined the AGN monochromatic luminosity at 5100\AA\ $\lambda L_\lambda = \left(5.75\pm0.40\right)\times 10^{39}\,\mathrm{erg\,s^{-1}}$, after subtracting the contribution of the nuclear star cluster. While the optical luminosity of NGC 4395 is two orders of magnitude lower than that of other reverberation-mapped AGNs, NGC 4395 follows the size-luminosity relation, albeit with an offset of 0.48 dex ($\geq$2.5$\sigma$) from the previous best-fit relation of Bentz et al. (2013).


arXiv:2002.08031v1 [pdf, other]
Discovery of a pre-cataclysmic binary with unusual chromaticity of the eclipsed white dwarf by the GPX Survey
Comments: 11 pages 6 figures, accepted for publication in MNRAS

We report the discovery of a relatively bright eclipsing binary system, which consists of a white dwarf and a main sequence K7 star with clear signs of chromospheric and spot activity. The light curve of this system shows $\sim0.2$mag ellipsoidal variability with a period of 0.297549d and a short total eclipse of the white dwarf. Based on our analysis of the spectral and photometric data, we estimated the parameters of the system. The K7V star is tidally deformed but does not fill its Roche lobe (the filling factor is about 0.86). The orbital inclination is $i=73^\circ.1\pm 0^\circ.2$, the mass ratio is $q=M_2/M_1\approx 0.88$. The parameters of the K7V star are $M_2\approx 0.64$M$_{\odot}$, $R_2=0.645\pm 0.012$R$_{\odot}$, $T_2\approx 4070$K. The parameters of the white dwarf are $M_1\approx 0.72$M$_{\odot}$, $R_1=0.013\pm 0.003$R$_{\odot}$, $T_1=8700\pm 1100$K. Photometric observations in different bands revealed that the maximum depth of the eclipse is in the \textit{SDSS r} filter, which is unusual for a system of a white dwarf and a late main sequence star. We suspect that this system is a product of the evolution of a common envelope binary star, and that the white dwarf accretes the stellar wind from the secondary star (the so-called low-accretion rate polar, LARP).


arXiv:2002.08036v1 [pdf, other]
Architecture of three-planet systems predicted from the observed protoplanetary disk of HL Tau
Comments: 16 pages, 9 figures. Accepted for publication in the ApJ

A number of protoplanetary disks observed with ALMA potentially provide direct examples of initial conditions for planetary systems. In particular, the HL Tau disk has been intensively studied, and its rings/gaps are conventionally interpreted to be a result of unseen massive planets embedded in the gaps. Based on this interpretation, we carried out N-body simulations to investigate orbital evolution of planets within the protoplanetary disk and after the disk dispersal. Before the disk dispersal, our N-body simulations include both migration and mass-growth of the planet coupled with evolution of the disk. By varying the disk parameters, we produce a variety of widely-separated planetary systems consisting of three super-Jupiters at the end of disk dispersal. We found the outer planet is more massive than the inner one, and the migration of the innermost planet is inefficient due to the accretion of outer planet(s). We also showed how the final configuration and the final planetary mass depend on disk parameters. The migration is found to be convergent and no planet-pair has a period ratio less than 2. After the disk dispersal, we switch to pure gravitational N-body simulations and integrate the orbits up to 10 Gyr. Most simulated systems remain stable for at least 10 Gyr. We discuss implications of our result in terms of the observed widely-separated planetary systems HR 8799 and PDS 70.


arXiv:2002.08050v1 [pdf, other]
On The Formation Of Low-Spinning 100 Msun Black Holes
Comments: 4 pages + refs, comments welcomed

It is speculated that a merger of two massive astrophysical black holes in dense stellar environment may lead to the formation of a massive black hole in the pair-instability mass gap (70/80-125 Msun). Such a merger-formed black hole is expected to typically have a high spin (a=0.7), however, with a broad spectrum of spins being allowed (0<a<1). If such massive black hole acquires another black hole it may lead to another merger detectable by LIGO/Virgo in gravitational waves. We show that it is highly unlikely to form in this way and retain a 100 Msun black hole in a globular cluster if the black hole's spin is low (a<0.3). Massive merger-formed black holes with low spins acquire high recoil speeds (> 200 km/s) from gravitational-wave kick during formation that exceed typical escape speeds from globular clusters (50 km/s). However, a very low-spinning (a=0.1) and massive (100 Msun) black hole could be formed this way and retained in a galactic nuclear star cluster. Even though massive, merger-formed black holes with such low spins acquire high speeds during formation (400 km/s), they may avoid ejection since massive nuclear clusters have high escape velocities (300-500 km/s). This adds to already existing astrophysical scenarios of the formation of massive black holes with low spins. A future detection of a massive black hole in the pair-instability mass gap with low spin is therefore not a proof of the existence of primordial black holes, which are sometimes claimed to have low spins and arbitrarily high masses (not affected by pair-instability).


arXiv:2002.08069v1 [pdf, other]
White Dwarfs as Advanced Physics Laboratories. The Axion case
Comments: Accepted for publication in the Proceedings of the IAU Symposium 357: White Dwarfs as Probes of Fundamental Physics and Tracers of Planetary, Stellar, and Galactic Evolution. 10 figures

The shape of the luminosity function of white dwarfs (WDLF) is sensitive to the characteristic cooling time and, therefore, it can be used to test the existence of additional sources or sinks of energy such as those predicted by alternative physical theories. However, because of the degeneracy between the physical properties of white dwarfs and the properties of the Galaxy, the star formation history (SFH) and the IMF, it is almost always possible to explain any anomaly as an artifact introduced by the star formation rate. To circumvent this problem there are at least two possibilities, the analysis of the WDLF in populations with different stories, like disc and halo, and the search of effects not correlated with the SFH. These procedures are illustrated with the case of axions.


arXiv:2002.08072v1 [pdf, other]
The Stellar Variability Noise Floor for Transiting Exoplanet Photometry with PLATO
Comments: 11 pages, 8 figures, accepted in MNRAS

One of the main science motivations for the ESA PLAnetary Transit and Oscillations (PLATO) mission is to measure exoplanet transit radii with 3% precision. In addition to flares and starspots, stellar oscillations and granulation will enforce fundamental noise floors for transiting exoplanet radius measurements. We simulate light curves of Earth-sized exoplanets transiting continuum intensity images of the Sun taken by the HMI instrument aboard SDO to investigate the uncertainties introduced on the exoplanet radius measurements by stellar granulation and oscillations. After modeling the solar variability with a Gaussian process, we find that the amplitude of solar oscillations and granulation is of order 100 ppm -- similar to the depth of an Earth transit -- and introduces a fractional uncertainty on the depth of transit of 0.73% assuming four transits are observed over the mission duration. However, when we translate the depth measurement into a radius measurement of the planet, we find a much larger radius uncertainty of 3.6%. This is due to a degeneracy between the transit radius ratio, the limb-darkening, and the impact parameter caused by the inability to constrain the transit impact parameter in the presence of stellar variability. We find that surface brightness inhomogeneity due to photospheric granulation contributes a lower limit of only 2 ppm to the photometry in-transit. The radius uncertainty due to granulation and oscillations, combined with the degeneracy with the transit impact parameter, accounts for a significant fraction of the error budget of the PLATO mission, before detector or observational noise is introduced to the light curve. If it is possible to constrain the impact parameter or to obtain follow-up observations at longer wavelengths where limb-darkening is less significant, this may enable higher precision radius measurements.


arXiv:2002.08077v1 [pdf, other]
The role of disc torques in forming resonant planetary systems
Comments: 7 pages, 7 figures, accepted for publication in A&A

The most accurate method for modelling planetary migration and hence the formation of resonant systems is using hydrodynamical simulations. Usually, the force (torque) acting on a planet is calculated using the forces from the gas disc and the star, while the gas accelerations are computed using the pressure gradient, the star, and the planet's gravity, ignoring its own gravity. For the non-migrating the neglect of the disc gravity results in a consistent torque calculation while for the migrating case it is inconsistent. We aim to study how much this inconsistent torque calculation can affect the final configuration of a two-planet system. Our focus will be on low-mass planets because most of the multi-planetary systems, discovered by the Kepler survey, have masses around 10 Earth masses. Performing hydrodynamical simulations of planet-disc interaction, we measure the torques on non-migrating and migrating planets for various disc masses as well as density and temperature slopes with and without considering the disc self-gravity. Using this data, we find a relation that quantifies the inconsistency, use it in an N-body code, and perform an extended parameter study modelling the migration of a planetary system with different planet mass ratios and disc surface densities, in order to investigate the impact of the torque inconsistency on the architecture of the planetary system. Not considering disc self-gravity produces an artificially larger torque on the migrating planet that can result in tighter planetary systems. The deviation of this torque from the correct value is larger in discs with steeper surface density profiles. In hydrodynamical modelling of multi-planetary systems, it is crucial to account for the torque correction, otherwise the results favour more packed systems.


arXiv:2002.08078v1 [pdf, other]
EXTraS discovery of an X-ray superflare from an L dwarf
Comments: 5 pages, 3 figures. Published as a Letter to A&A

We present the first detection of an X-ray flare from an ultracool dwarf of spectral class L. The event was identified in the EXTraS database of XMM-Newton variable sources, and its optical counterpart, J0331-27, was found through a cross-match with the Dark Energy Survey Year 3 release. Next to an earlier four-photon detection of Kelu-1, J0331-27 is only the second L dwarf detected in X-rays, and much more distant than other ultracool dwarfs with X-ray detections (photometric distance of 240 pc). From an optical spectrum with the VIMOS instrument at the VLT, we determine the spectral type of J0331-27 to be L1. The X-ray flare has an energy of E_X,F ~ 2x10^33 erg, placing it in the regime of superflares. No quiescent emission is detected, and from 2.5 Msec of XMM data we derive an upper limit of L_X,qui < 10^27 erg/s. The flare peak luminosity L_X,peak = 6.3x10^29 erg/s, flare duration tau_decay ~ 2400 s, and plasma temperature (~16 MK) are similar to values observed in X-ray flares of M dwarfs. This shows that strong magnetic reconnection events and the ensuing plasma heating are still present even in objects with photospheres as cool as ~2100 K. However, the absence of any other flares above the detection threshold of E_X,F ~2.5x10^32 erg in a total of ~2.5 Ms of X-ray data yields a flare energy number distribution inconsistent with the canonical power law dN/dE ~ E^-2, suggesting that magnetic energy release in J0331-27 -- and possibly in all L dwarfs -- takes place predominantly in the form of giant flares.


arXiv:2002.08135v1 [pdf, other]
Investigating Taxonomic Diversity within Asteroid Families through ATLAS Dual-Band Photometry
Comments: No comment found

We present here the c-o colors for identified Flora, Vesta, Nysa-Polana, Themis, and Koronis family members within the historic data set (2015-2018) of the Asteroid Terrestrial-impact Last Alert System (ATLAS). The Themis and Koronis families are known to be relatively pure C- and S-type Bus-DeMeo taxonomic families, respectively, and the extracted color data from the ATLAS broadband c- and o-filters of these two families is used to demonstrate that the ATLAS c-o color is a sufficient parameter to distinguish between the C- and S-type taxonomies. The Vesta and Nysa-Polana families are known to display a mixture of taxonomies possibly due to Vesta's differentiated parent body origin and Nysa-Polana actually consisting of two nested families with differing taxonomies. Our data show that the Flora family also displays a large degree of taxonomic mixing and the data reveal a substantial H-magnitude dependence on color. We propose and exclude several interpretations for the observed taxonomic mix. Additionally, we extract rotation periods of all of the targets reported here and find good agreement with targets that have previously reported periods.


arXiv:2002.08140v1 [pdf, other]
Detection of the thermonuclear X-ray bursts and dips from the X-ray binary 4U 1323-62 with AstroSat/LAXPC
Comments: No comment found

Using data from the Large Area X-ray Proportional Counter (LAXPC) on the \textit{AstroSat} satellite, we observed the Type-1 thermonuclear X-ray bursts from the Low Mass X-ray Binary Neutron Star 4U 1323-62. The observations of 4U 1323-62 were carried out during the performance verification phase of the \textit{AstroSat} satellite showed six thermonuclear X-ray bursts in a total effective exposure of $\sim$ 49.5 ks for about two consecutive days. Recurrence time of the detected thermonuclear bursts is in accordance with the orbital period of the source $\sim$ 9400 seconds. Moreover, the light curve of 4U 1323-62 revealed the presence of two dips. We presented the results from time-resolved spectroscopy performed during all of the six X-ray bursts and also report the detection of a known low frequency Quasi-periodic oscillation (LFQPO) at $\sim$ 1 Hz, from the source. However, any evidence of kilohertz QPO was not found. We have shown the burst profile at different energy ranges. Assuming a distance of 10 kpc, we observed a mean flux $\sim$ 1.8 $\times$ $10^{-9}$ erg $cm^2$ $s^{-1}$. The radius of the blackbody is found to be highly consistent with the blackbody temperature and the blackbody flux of the bursts.


arXiv:2002.08185v1 [pdf, other]
Properties of Trans-fast Magnetosonic Jets in Black Hole Magnetospheres
Comments: accpeted for publication in the Astrophysical Journal

Traveling across several order of magnitude in distance, relativistic jets from strong gravity region to asymptotic flat spacetime region are believed to consist of several general relativistic magnetohydrodynamic (GRMHD) processes. We present a semi-analytical approach for modeling the global structures of a trans-fast magnetosonic relativistic jet, which should be ejected from a plasma source nearby a black hole in a funnel region enclosed by dense accreting flow and also disk corona around the black hole. Our model consistently includes the inflow and outflow part of the GRMHD solution along the magnetic field lines penetrating the black hole horizon. After the rotational energy of the black hole is extracted electromagnetically by the negative energy GRMHD inflow, the huge electromagnetic energy flux then propagates from the inflow to the outflow region across the plasma source, and in the outflow region the electromagnetic energy converts to the fluid kinetic energy. Eventually, the accelerated outflow must exceed the fast-magnetosonic wave speed. We apply the semi-analytical trans-fast magnetosonic flow model to the black hole magnetosphere for both parabolic and split-monopole magnetic field configurations, and discuss the general flow properties; that is, jet acceleration, jet magnetization, and the locations of some characteristic surfaces of the black hole magnetosphere. We have confirmed that, at large distance, the GRMHD jet solutions are in good agreement with the previously known trans-fast special relativistic magnetohydrodynamic (SRMHD) jet properties, as expected. The flexibility of the model provides a prompt and heuristic way to approximate the global GRMHD trans-fast magnetosonic jet properties.


arXiv:2002.08189v1 [pdf, other]
Discovery of technetium- and niobium-rich S stars: the case for bitrinsic stars
Comments: A & A Letters, accepted for publication

S stars are late-type giants with overabundances of s-process elements. They come in two flavours depending on the presence or not of technetium (Tc), an element without stable isotopes. Intrinsic S stars are Tc-rich and genuine asymptotic giant branch (AGB)stars while extrinsic S stars owe their s-process overabundances to the pollution from a former AGB companion, now a white dwarf(WD). In addition to Tc, another distinctive feature between intrinsic and extrinsic S stars is the overabundance of niobium (Nb) in the latter class. We discuss the case of the S stars BD+79 156 and o1Ori whose specificity is to share the distinctive features of both intrinsic and extrinsic S stars, namely the presence of Tc along with a Nb overabundance. BD+79 156 is the first clear case of a bitrinsic star, i.e. a doubly s-process-enriched object, first through mass transfer in a binary system, and then through internal nucleosynthesis (responsible for the Tc-enrichment in BD+79 156 which must therefore have reached the AGB phase of its evolution). This hybrid nature of the s-process pattern in BD+79 156 is supported by its binary nature and its location in the HR diagram just beyond the onset of the third dredge-up on the AGB. The Tc-rich, binary S-star o1Ori with a WD companion was another long-standing candidate for a similar hybrid s-process enrichment. However the marginal overabundance of Nb derived ino1Ori does not allow to trace unambiguously the evidence of a large pollution coming from the AGB progenitor of its current WD companion. As a side product, the current study offers a new way of detecting binary AGB stars with WD companions by identifying their Tc-rich nature along with a Nb overabundance.


arXiv:2002.08194v1 [pdf, other]
On the Likelihood of Observing Extragalactic Civilizations: Predictions from the Self-Indication Assumption
Comments: 9 pages, 5 figures

Ambitious civilizations that expand for resources at an intergalactic scale could be observable from a cosmological distance, but how likely is one to be visible to us? The question comes down to estimating the appearance rate of such things in the cosmos --- a radically uncertain quantity. Despite this prior uncertainty, anthropic considerations give rise to Bayesian updates, and thus predictions. The Self-Sampling Assumption (SSA), a school of anthropic probability, has previously been used for this purpose. Here, we derive predictions from the alternative school, the Self-Indication Assumption (SIA), and point out its features. SIA favors a higher appearance rate of expansionistic life, but our existence at the present cosmic time means that such life cannot be too common (else our galaxy would long ago have been overrun). This combination squeezes our vast prior uncertainty into a few orders of magnitude. Details of the background cosmology fall out, and we are left with some stark conclusions. E.g. if the limits to technology allow a civilization to expand at speed $v$, the probability of at least one expanding cosmological civilization being visible on our past light cone is $1-\frac{v^3}{c^3}$. We also show how the SIA estimate can be updated from the results of a hypothetical full-sky survey that detects "$n$" expanding civilizations (for $n \geq 0$), and calculate the implied final extent of life in the universe.


arXiv:2002.08200v1 [pdf, other]
Sensitivity of the lower-edge of the pair instability black hole mass gap to the treatment of time dependent convection
Comments: 7 pages + 1 appendix, accepted in MNRAS, online results at https://zenodo.org/record/3406320

Gravitational-wave detections are now probing the black hole (BH) mass distribution, including the predicted pair-instability mass gap. These data require robust quantitative predictions, which are challenging to obtain. The most massive BH progenitors experience episodic mass ejections on timescales shorter than the convective turn-over timescale. This invalidates the steady-state assumption on which the classic mixing-length theory relies. We compare the final BH masses computed with two different versions of the stellar evolutionary code \texttt{MESA}: (i) using the default implementation of \cite{paxton:18} and (ii) solving an additional equation accounting for the timescale for convective deceleration. In the second grid, where stronger convection develops during the pulses and carries part of the energy, we find weaker pulses. This leads to lower amounts of mass being ejected and thus higher final BH masses of up to $\sim$\,$5\,M_\odot$. The differences are much smaller for the progenitors which determine the maximum mass of BHs below the gap. This prediction is robust at $M_{\rm BH, max}\simeq 48\,M_\odot$, at least within the idealized context of this study. This is an encouraging indication that current models are robust enough for comparison with the present-day gravitational-wave detections. However, the large differences between individual models emphasize the importance of improving the treatment of convection in stellar models, especially in the light of the data anticipated from the third generation of gravitational wave detectors.


arXiv:2002.08217v1 [pdf, other]
Model of a gap formed by a planet with fast inward migration
Comments: 15 pages, 15 figures, accepted for publication in The Astrophysical Journal

A planet is formed within a protoplanetary disk. Recent observations have revealed substructures such as gaps and rings, which may indicate forming planets within the disk. Due to disk--planet interaction, the planet migrates within the disk, which can affect a shape of the planet-induced gap. In this paper, we investigate effects of fast inward migration of the planet on the gap shape, by carrying out hydrodynamic simulations. We found that when the migration timescale is shorter than the timescale of the gap-opening, the orbital radius is shifted inward as compared to the radial location of the gap. We also found a scaling relation between the radial shift of the locations of the planet and the gap as a function of the ratio of the timescale of the migration and gap-opening. Our scaling relation also enables us to constrain the gas surface density and the viscosity when the gap and the planet are observed. Moreover, we also found the scaling relation between the location of the secondary gap and the aspect ratio. By combining the radial shift and the secondary gap, we may constrain the physical condition of the planet formation and how the planet evolves in the protoplanetary disk, from the observational morphology.


arXiv:2002.08227v1 [pdf, other]
Can we detect the stellar differential rotation of WASP-7 through theRossiter-McLaughlin observations?
Comments: 12 pages plus appendix, 9 figures

The Rossiter-McLaughlin (RM) effect is the radial velocity signal generated when an object transits a rotating star. Stars rotate differentially and this affects the shape and amplitude of this signal, on a level that can no longer be ignored with precise spectrographs. Highly misaligned planets provide a unique opportunity to probe stellar differential rotation via the RM effect, as they cross several stellar latitudes. In this sense, WASP-7, and its hot Jupiter with a projected misalignment of \sim 90{\deg}, is one of the most promising targets. The aim of this work is to understand if the stellar differential rotation is measurable through the RM signal for systems with a geometry similar to WASP-7. In this sense, we use a modified version of SOAP3.0 to explore the main hurdles that prevented the precise determination of the differential rotation of WASP-7. We also investigate whether the adoption of the next generation spectrographs, like ESPRESSO, would solve these issues. Additionally, we assess how instrumental and stellar noise influence this effect and the derived geometry of the system. We found that, for WASP-7, the white noise represents an important hurdle in the detection of the stellar differential rotation, and that a precision of at least 2m/s or better is essential.


arXiv:2002.08238v1 [pdf, other]
Beyond power spectrum I: recovering HII bubble size distribution from 21cm power spectrum with artificial neural network
Comments: 12 pages, 12 figures. Submitted to MNRAS

The bubble size distribution of ionized hydrogen regions, which could be derived from the tomographic imaging data of the redshifted 21~cm signal from the epoch of reionization, probes the information about the morphology of \HII\ bubbles during the reionization. However, 21~cm imaging is observationally very challenging even for the upcoming large radio interferometers. Given that these interferometers promise to measure the 21~cm power spectrum accurately, we propose a new method, which is based on the artificial neural networks (ANN), to reconstruct the \HII\ bubble size distribution from the 21~cm power spectrum. We demonstrate that the reconstruction from the 21~cm power spectrum can be almost as accurate as directly measured from the imaging data with the fractional error $\lesssim 10\%$, even with thermal noise at the sensitivity level of the Square Kilometre Array. Nevertheless, systematic errors might arise from approximations made in reionization simulations used for training the ANN. This paper, as the first in a series, exemplifies the possibility of recovering from the 21~cm power spectrum with ANN additional statistics of cosmic reionization that could not otherwise be inferred from the power spectrum analysis directly in the conventional methods.


arXiv:2002.08257v1 [pdf, other]
An X-ray View of the Hot Circum-Galactic Medium
Comments: 7 pages, 2 figures, 3 tables; AN in press; invited review for the XMM-Newton 2019 science workshop "Astrophysics of Hot Plasma in Extended X-ray Sources"

The hot circum-galactic medium (CGM) represents the hot gas distributed beyond the stellar content of the galaxies while typically within their dark matter halos. It serves as a depository of energy and metal-enriched materials from galactic feedback and a reservoir from which the galaxy acquires fuels to form stars. It thus plays a critical role in the coevolution of galaxies and their environments. X-rays are one of the best ways to trace the hot CGM. I will briefly review what we have learned about the hot CGM based on X-ray observations over the past two decades, and what we still do not know. I will also briefly prospect what may be the foreseeable breakthrough in the next one or two decades with future X-ray missions.


arXiv:2002.08262v1 [pdf, other]
Characterizing the spatial pattern of solar supergranulation using the bispectrum
Comments: 16 pages, 12 figures, accepted for publication by A&A

Context. The spatial power spectrum of supergranulation does not fully characterize the underlying physics of turbulent convection. For example, it does not describe the non-Gaussianity in the horizontal flow divergence. Aims. Our aim is to statistically characterize the spatial pattern of solar supergranulation beyond the power spectrum. The next-order statistic is the bispectrum. It measures correlations of three Fourier components and is related to the nonlinearities in the underlying physics. Methods. We estimated the bispectrum of supergranular horizontal surface divergence maps that were obtained using local correlation tracking (LCT) and time-distance helioseismology (TD) from one year of data from the Helioseismic and Magnetic Imager on-board the Solar Dynamics Observatory starting in May 2010. Results. We find significantly nonzero and consistent estimates for the bispectrum. The strongest nonlinearity is present when the three coupling wave vectors are at the supergranular scale. These are the same wave vectors that are present in regular hexagons, which were used in analytical studies of solar convection. At these Fourier components, the bispectrum is positive, consistent with the positive skewness in the data and with supergranules preferentially consisting of outflows surrounded by a network of inflows. We use the bispectrum to generate synthetic divergence maps that are very similar to the data by a model that consists of a Gaussian term and a weaker quadratic nonlinear component. Thereby, we estimate the fraction of the variance in the divergence maps from the nonlinear component to be of the order of 4-6%. Conclusions. We propose that bispectral analysis is useful for understanding solar turbulent convection, for example for comparing observations and numerical models of supergranular flows. This analysis may also be useful to generate synthetic flow fields.


arXiv:2002.08268v1 [pdf, other]
Wind nebulae and supernova remnants of very massive stars
Comments: Accepted at MNRAS

A very small fraction of (runaway) massive stars have masses exceeding $60$-$70\, \rm M_{\odot}$ and are predicted to evolve as Luminous-Blue-Variable and Wolf-Rayet stars before ending their lives as core-collapse supernovae. Our 2D axisymmetric hydrodynamical simulations explore how a fast wind ($2000\, \rm km\, \rm s^{-1}$) and high mass-loss rate ($10^{-5}\, \rm M_{\odot}\, \rm yr^{-1}$) can impact the morphology of the circumstellar medium. It is shaped as 100 pc-scale wind nebula which can be pierced by the driving star when it supersonically moves with velocity $20$-$40\, \rm km\, \rm s^{-1}$ through the interstellar medium (ISM) in the Galactic plane. The motion of such runaway stars displaces the position of the supernova explosion out of their bow shock nebula, imposing asymmetries to the eventual shock wave expansion and engendering Cygnus-loop-like supernova remnants. We conclude that the size (up to more than $200\, \rm pc$) of the filamentary wind cavity in which the chemically enriched supernova ejecta expand, mixing efficiently the wind and ISM materials by at least $10\%$ in number density, can be used as a tracer of the runaway nature of the very massive progenitors of such $0.1\, \rm Myr$ old remnants. Our results motivate further observational campaigns devoted to the bow shock of the very massive stars BD+43 3654 and to the close surroundings of the synchrotron-emitting Wolf-Rayet shell G2.4+1.4.


arXiv:2002.08271v1 [pdf, other]
Polarization loss in reflecting coating
Comments: No comment found

In laser gravitational waves detectors optical loss restricts sensitivity. We discuss polarization scattering as one more possible mechanism of optical losses. Circulated inside interferometer light is polarized and after reflection its plane of polarization can turn a little due to reflecting coating of mirror can have slightly different refraction index along axes $x,\, y$ in plane of mirror surface (optical anisotropy). This anisotropy can be produced during manufacture of coating (elasto-optic effect). This orthogonal polarized light, enhanced in cavity, produces polarization optical loss. Polarization map of mirrors is very important and we propose to measure it. Polarization loss can be important in different precision optical experiments based on usage of polarized light, for example, in quantum speed meter.


arXiv:2002.08278v1 [pdf, other]
Constraining stellar population parameters from narrow band photometric surveys using convolutional neural networks
Comments: 9 pages, 10 figures, 2 tables. Submitted to MNRAS

Upcoming large-area narrow band photometric surveys, such as J-PAS, will enable us to observe a large number of galaxies simultaneously and efficiently. However, it will be challenging to analyse the spatially-resolved stellar populations of galaxies from such big data to investigate galaxy formation and evolutionary history. We have applied a convolutional neural network (CNN) technique, which is known to be computationally inexpensive once it is trained, to retrieve the metallicity and age from J-PAS-like narrow band images. The CNN was trained using mock J-PAS data created from the CALIFA IFU survey and the age and metallicity at each data point, which are derived using full spectral fitting to the CALIFA spectra. We demonstrate that our CNN model can consistently recover age and metallicity from each J-PAS-like spectral energy distribution. The radial gradients of the age and metallicity for galaxies are also recovered accurately, irrespective of their morphology. However, it is demonstrated that the diversity of the dataset used to train the neural networks has a dramatic effect on the recovery of galactic stellar population parameters. Hence, future applications of CNNs to constrain stellar populations will rely on the availability of quality spectroscopic data from samples covering a wide range of population parameters.


arXiv:2002.08291v1 [pdf, other]
Extending the PyCBC offline search to a global detector network
Comments: 12 pages, 6 figures

The worldwide advanced gravitational-wave (GW) detector network has so far primarily consisted of the two Advanced LIGO observatories at Hanford and Livingston, with Advanced Virgo joining the 2016-7 O2 observation run at a relatively late stage. However, in the O3 science run three detectors have been simultaneously operating at all times. In the near future, the KAGRA detector will join the global network and a further LIGO detector in India is under construction. Gravitational-wave search methods must therefore be able to analyse data from an arbitrary network of detectors. In this paper we extend the PyCBC offline compact binary coalescence (CBC) search analysis to three or more detectors, and describe resulting updates to the coincident search and event ranking statistic. For a three-detector network, our improved multi-detector search finds 20% more simulated signals at fixed false alarm rate in idealized colored Gaussian noise, and up to 40% more in real data, compared to the two-detector analysis previously used during O2.


arXiv:2002.08297v1 [pdf, other]
A Binary Comb Model for Periodic Fast Radio Bursts
Comments: 8 pages, 2 figures

We show that the periodic FRB 180916.J0158+65 can be interpreted by invoking an interacting neutron star binary system with an orbital period of $\sim 16$ d. The FRBs are produced by a highly magnetized pulsar, whose magnetic field is "combed" by the strong wind from a companion star, either a massive star or a millisecond pulsar. The FRB pulsar wind retains a clear funnel in the companion's wind that is otherwise opaque to induced Compton or Raman scatterings for repeating FRB emission. The 4-day active window corresponds to the time when the funnel points towards Earth. The comb also perturbs the magnetosphere of the FRB pulsar and may trigger emission of FRBs. We derive the physical constraints on the comb and the FRB pulsar from the observations and estimate the event rate of FRBs. In this scenario, a lower limit on the period of observable FRBs is predicted. We speculate that both the intrinsic factors (strong magnetic field and young age) and the extrinsic factor (combing) may be needed to generate FRBs in neutron star binary systems.


arXiv:2002.08319v1 [pdf, other]
Spectral and atmospheric characterisation of a new benchmark brown dwarf HD13724B
Comments: 11 pages, Accepted to A&A. arXiv admin note: text overlap with arXiv:1712.05217

Context. HD13724 is a nearby solar-type star at 43.48 $\pm$ 0.06 pc hosting a long-period low-mass brown dwarf detected with the CORALIE echelle spectrograph as part of the historical CORALIE radial-velocity search for extra-solar planets. The companion has a minimum mass of $26.77^{+4.4}_{-2.2} M_{\mathrm{Jup}}$ and an expected semi-major axis of $\sim$ 240 mas making it a suitable target for further characterisation with high-contrast imaging, in particular to measure its inclination, mass, and spectrum and thus establish its substellar nature. Aims. Using high-contrast imaging with the SPHERE instrument on the Very Large Telescope (VLT), we are able to directly image a brown dwarf companion to HD13724 and obtain a low-resolution spectrum. Methods. We combine the radial-velocity measurements of CORALIE and HARPS taken over two decades and high contrast imaging from SPHERE to obtain a dynamical mass estimate. From the SPHERE data we obtain a low resolution spectrum of the companion from Y to J band, as well as photometric measurements from IRDIS in the J, H and K bands. Results. Using high-contrast imaging with the SPHERE instrument at the VLT, we report the first images of a brown dwarf companion to the host star HD13724. It has an angular separation of 175.6 $\pm$ 4.5 mas and H-band contrast of $10.61\pm0.16$ mag and, using the age estimate of the star to be $\sim$1 Gyr, gives an isochronal mass estimate of $\sim$44 $M_{\mathrm{Jup}}$. By combining radial-velocity and imaging data we also obtain a dynamical mass of $50.5^{+3.3}_{-3.5} M_{\mathrm{Jup}}$. Through fitting an atmospheric model, we estimate a surface gravity of $\log g = 5.5$ and an effective temperature of 1000K. A comparison of its spectrum with observed T dwarfs estimates a spectral type of T4 or T4.5, with a T4 object providing the best fit.


arXiv:2002.08353v1 [pdf, other]
ZFIRE: Measuring Electron Density with [OII] as a function of environment at z = 1.62
Comments: 18 Pages, 6 figures, 3 tables, Accepted for publication in Astrophysical Journal

The global star formation rates (SFR) of galaxies at fixed stellar masses increase with redshift and are known to vary with environment unto z~2. We explore here whether the changes in the star formation rates can also apply to the electron densities of the inter-stellar medium (ISM) by measuring the [OII] (3727A/3729A) ratio for cluster and field galaxies at z~2. We measure a median electron density of ne = 366+/-84 cm-3 for six galaxies (with 1-sigma scatter = 163 cm-3) in the UDS proton-cluster at z=1.62. We find that the median electron density of galaxies in the UDS photo-cluster environment is three times higher compared to the median electron density of field galaxies (ne = 113+/- 63 cm-3 and 1-sigma scatter = 79 cm-3) at comparable redshifts, stellar mass and SFR. However, we note that a sample of six photo-cluster galaxies is insufficient to reliably measure the electron density in the average porto-cluster environment at z~2. We conclude that the electron density increases with redshift in both cluster and field environments up to z~2 (ne = 30 +/- 1 cm-3 for z ~ 0 to ne =254+/- 76 cm-3 for z~1.5). We find tentative evidence (~2.6 sigma ) for a possible dependence of electron density on environment, but the results require confirmation with larger sample sizes.