### 68 articles on Sunday, November 18

arXiv:1811.05978v1 [pdf, other]
On the robustness of analysis techniques for molecular detections using high resolution exoplanet spectroscopy
Comments: 15 pages, 16 figures, Accepted for publication in MNRAS

High-resolution doppler spectroscopy provides a powerful means for chemical detections in exoplanetary atmospheres. This approach involves monitoring hundreds of molecular lines in the planetary spectrum doppler shifted by the orbital motion of the planet. The molecules are detected by cross-correlating the observed spectrum of the system with a model planetary spectrum. The method has led to molecular detections of H2O, CO, and TiO in hot Jupiters using large ground-based telescopes. Critical to this method, however, is the accurate removal of the stellar and telluric features from the observed spectrum, also known as detrending. Previous molecular detections have relied on specific choices of detrending methods and parameters. However, the robustness of molecular detections across the different choices has not been investigated in detail. We conduct a systematic investigation of the effect of detrending algorithms, parameters, and optimizations on chemical detections using high-resolution spectroscopy. As a case study, we consider the hot Jupiter HD 189733 b. Using multiple methods, we confirm high-significance detections of H2O (4.8$\sigma$) and CO (4.7$\sigma$). Additionally, we report evidence for HCN at high significance (5.0$\sigma$). On the other hand, our results highlight the need for improved metrics and extended observations for robust confirmations of such detections. In particular, we show that detection significances of $\gtrsim$ 4$\sigma$ can be obtained by optimizing detrending at incorrect locations in the planetary velocity space; such false positives can occur in nearly 30\% of cases. We discuss approaches to help distinguish molecular detections from spurious noise.

arXiv:1811.05980v1 [pdf, other]
Inferring a difference in the star-forming properties of lower versus higher X-ray luminosity AGNs
Comments: 6 pages, 4 figures, Accepted for publication in MNRAS Letter

We explore the distribution of RMS=SFR/SFR_MS (where SFR_MS is the star formation rate of "Main Sequence" star-forming galaxies) for AGN hosts at z=1. We split our sample into two bins of X-ray luminosity divided at Lx=2x10^43erg s-1 to investigate whether the RMS distribution changes as a function of AGN power. Our main results suggest that, when the RMS distribution of AGN hosts is modelled as a log-normal distribution (i.e. the same shape as that of MS galaxies), galaxies hosting more powerful X-ray AGNs (i.e. Lx>2x10^43erg s-1) display a narrower RMS distribution that is shifted to higher values compared to their lower Lx counterparts. In addition, we find that more powerful X-ray AGNs have SFRs that are more consistent with that of MS galaxies compared to lower Lx AGNs. Despite this, the mean SFRs (as opposed to RMS) measured from these distributions are consistent with the previously observed flat relationship between SFR and Lx. Our results suggest that the typical star-forming properties of AGN hosts change with Lx , and that more powerful AGNs typically reside in more MS-like star-forming galaxies compared to lower Lx AGNs.

arXiv:1811.05981v1 [pdf, other]
Evidence for mass accretion driven by spiral shocks onto the white dwarf in SDSS J123813.73-033933.0
Comments: 26 pages, 22 figures. Accepted for publication in MNRAS

We present high-time-resolution photometry and phase-resolved spectroscopy of the short-period ($P_\mathrm{orb} = 80.52\,\mathrm{min}$) cataclysmic variable SDSS J123813.73-033933.0, observed with the $\mathit{Hubble}$ $\mathit{Space}$ $\mathit{Telescope}$ $\mathit{(HST)}$, the $\mathit{Kepler/K2}$ mission and the Very Large Telescope (VLT). We also report observations of the first detected super-outburst. SDSS J1238-0339 shows two types of variability: quasi-regular brightenings recurring every $\simeq 8.5$ h during which the system increases in brightness by $\simeq 0.5$mag, and a double hump quasi-sinusoidal modulation at the orbital period. The detailed $\mathit{K2}$ light curve reveals that the amplitude of the double-humps increases during the brightenings and that their phase undergoes a $\simeq 90^{\circ}$ phase shift with respect to the quiescent intervals. The $\mathit{HST}$ data unambiguously demonstrate that these phenomena both arise from the heating and cooling of two relatively large regions on the white dwarf. We suggest that the double-hump modulation is related to spiral shocks in the accretion disc resulting in an enhanced accretion rate heating two localised regions on the white dwarf, with the structure of the shocks fixed in the binary frame explaining the period of the double humps. The physical origin of the 8.5 h brightenings is less clear. However, the correlation between the observed variations of the amplitude and phase of the double-humps with the occurrence of the brightenings is supportive of an origin in thermal instabilities in the accretion disc.

arXiv:1811.05982v1 [pdf, other]
The Shapes of the Rotation Curves of Star-forming Galaxies Over the Last $\approx$10 Gyr

We analyse maps of the spatially-resolved nebular emission of $\approx$1500 star-forming galaxies at $z\approx0.6$-$2.2$ from deep KMOS and MUSE observations to measure the average shape of their rotation curves. We use these to test claims for declining rotation curves at large radii in galaxies at $z\approx1$-$2$ that have been interpreted as evidence for an absence of dark matter. We show that the shape of the average rotation curves, and the extent to which they decline beyond their peak velocities, depends upon the normalisation prescription used to construct the average curve. Normalising in size by the galaxy stellar disk-scale length ($R_{\rm{d}}$), we construct stacked position-velocity diagrams that trace the average galaxy rotation curve out to $6R_{\rm{d}}$ ($\approx$13 kpc, on average). Combining these curves with average HI rotation curves for local systems, we investigate how the shapes of galaxy rotation curves evolve over $\approx$10 Gyr. The average rotation curve for galaxies binned in stellar mass, stellar surface mass density and/or redshift is approximately flat, or continues to rise, out to at least $6R_{\rm{d}}$. We find a correlation between the outer slopes of galaxies' rotation curves and their stellar mass surface densities, with the higher surface density systems exhibiting flatter or less steeply rising rotation curves. Drawing comparisons with hydrodynamical simulations, we show that the average shapes of the rotation curves for our sample of massive, star-forming galaxies at $z\approx0$-$2.2$ are consistent with those expected from $\Lambda$CDM theory and imply dark matter fractions within $6R_{\rm{d}}$ of at least $\approx60$ percent.

arXiv:1811.05984v1 [pdf, other]
Scale-invariant alternatives to general relativity. III. The inflation--dark-energy connection

We discuss the cosmological phenomenology of biscalar-tensor models displaying a maximally symmetric Einstein-frame kinetic sector and constructed on the basis of scale symmetry and volume-preserving diffeomorphisms. These theories contain a single dimensionful parameter $\Lambda_0$-associated with the invariance under the aforementioned restricted coordinate transformations-and a massless dilaton field. At large field values these scenarios lead to inflation with no generation of isocurvature perturbations. The corresponding predictions depend only on two dimensionless parameters, which characterize the curvature of the field--manifold and the leading order behavior of the inflationary potential. For $\Lambda_0=0$ the scale symmetry is unbroken and the dilaton admits only derivative couplings to matter, evading all fifth force constraints. For $\Lambda_0\neq 0$ the field acquires a run-away potential that can support a dark energy dominated era at late times. We confront a minimalistic realization of this appealing framework with present data sets. The impact of possible consistency relations among the early and late Universe dynamics that could appear within this setting is also discussed.

arXiv:1811.05986v1 [pdf, other]
High-Resolution SOFIA/EXES Spectroscopy of $\mathrm{SO}_2$ Gas in the Massive Young Stellar Object MonR2 IRS3: Implications for the Sulfur Budget
Comments: 9 pages, 2 figures, accepted for publication in ApJL

Sulfur has been observed to be severely depleted in dense clouds leading to uncertainty in the molecules that contain it and the chemistry behind their evolution. Here, we aim to shed light on the sulfur chemistry in young stellar objects (YSOs) by using high-resolution infrared spectroscopy of absorption by the $\nu_3$ rovibrational band of SO$_2$ obtained with the Echelon-Cross-Echelle Spectrograph on the Stratospheric Observatory for Infrared Astronomy. Using local thermodynamic equilibrium models we derive physical parameters for the SO$_2$ gas in the massive YSO MonR2 IRS3. This yields a SO$_2$/$\mathrm{H}$ abundance lower limit of $5.6\pm0.5\times10^{-7}$, or $>\!4\%$ of the cosmic sulfur budget, and an intrinsic line width (Doppler parameter) of $b<3.20\;\mathrm{km\;s}^{-1}$. The small line widths and high temperature ($T_\mathrm{ex}=234\pm15\;\mathrm{K}$) locate the gas in a relatively quiescent region near the YSO, presumably in the hot core where ices have evaporated. This sublimation unlocks a volatile sulfur reservoir (e.g., sulfur allotropes as detected abundantly in comet 67P/Churyumov--Gerasimenko), which is followed by SO$_2$ formation by warm, dense gas-phase chemistry. The narrowness of the lines makes formation of SO$_2$ from sulfur sputtered off grains in shocks less likely toward MonR2 IRS3.

arXiv:1811.05987v1 [pdf, other]
The Non-Uniformity of Galaxy Cluster Metallicity Profiles
Comments: 19 pages, 13 figures, 3 tables. Accepted for publication in MNRAS

We study a sample of 207 nearby galaxy groups and clusters observed with XMM-Newton. Key aspects of this sample include the large size, the high data quality, and the large diversity of cluster dynamical states. We determine the overall metallicity within 0.3R$_{500}$ and the radial distribution of the metals. On average, we find a mild dependence of the core metallicity with the average temperature of the system in agreement with previous results. However, we identify the cause of this mild dependence to be due to relaxed systems only; disturbed systems do not show this trend, on average. The large scatter observed in this relation is strongly associated with the dynamical state of the systems: relaxed systems have on average a higher metallicity in the core than disturbed objects. The radial profiles of relaxed systems are centrally peaked and show a steep decrease with radius, flattening beyond 0.3-0.4R$_{500}$. The metallicity of disturbed systems is also higher in the center but at much lower values than what is observed for relaxed objects. This finding is consistent with the picture that cluster mergers mix the abundance distribution by inducing large scale motions. The scatter of the radial profiles is quite large, but while for relaxed systems it decreases almost monotonically as function of the radius, for disturbed systems it shows a significant boost at large radii. Systems with a central radio source have a flatter profile indicating that central AGNs are an efficient mechanism to uplift and redistribute the metals in the ICM.

arXiv:1811.05988v1 [pdf, other]
Constraints on Decaying Dark Matter from the Isotropic Gamma-Ray Background

If the dark matter is unstable, the decay of these particles throughout the universe and in the halo of the Milky Way could contribute significantly to the isotropic gamma-ray background (IGRB) as measured by Fermi. In this article, we calculate the high-latitude gamma-ray flux resulting from dark matter decay for a wide range of channels and masses, including all contributions from inverse Compton scattering and accounting for the production and full evolution of cosmological electromagnetic cascades. We also make use of recent multi-wavelength analyses that constrain the astrophysical contributions to the IGRB, enabling us to more strongly restrict the presence any component arising from decaying dark matter. Over a wide range of decay channels and masses (from GeV to EeV and above), we derive stringent lower limits on the dark matter's lifetime, generally in the range of $\tau \sim (1-5)\times 10^{28}$ s.

arXiv:1811.05989v1 [pdf, other]
Spatially resolving the atmosphere of the non-Mira-type AGB star SW Vir in near-infrared molecular and atomic lines with VLTI/AMBER
Comments: 8 pages, 6 figures, accepted for publication in Astronomy and Astrophysics

We present a near-infrared spectro-interferometric observation of the non-Mira-type, semiregular asymptotic giant branch star SW Vir. Our aim is to probe the physical properties of the outer atmosphere with spatially resolved data in individual molecular and atomic lines. We observed SW Vir in the spectral window between 2.28 and 2.31 micron with the near-infrared interferometric instrument AMBER at ESO's Very Large Telescope Interferometer (VLTI). Thanks to AMBER's high spatial resolution and high spectral resolution of 12000, the atmosphere of SW Vir has been spatially resolved not only in strong CO first overtone lines but also in weak molecular and atomic lines of H2O, CN, HF, Ti, Fe, Mg, and Ca. Comparison with the MARCS photospheric models reveals that the star appears larger than predicted by the hydrostatic models not only in the CO lines but also even in the weak molecular and atomic lines. We found that this is primarily due to the H2O lines (but also possibly due to the HF and Ti lines) originating in the extended outer atmosphere. Although the H2O lines manifest themselves very little in the spatially unresolved spectrum, the individual rovibrational H2O lines from the outer atmosphere can be identified in the spectro-interferometric data. Our modeling suggests an H2O column density of 10^{19}--10^{20} cm^{-2} in the outer atmosphere extending out to ~2 Rstar. Our study has revealed that the effects of the nonphotospheric outer atmosphere are present in the spectro-interferometric data not only in the strong CO first overtone lines but also in the weak molecular and atomic lines. Therefore, analyses of spatially unresolved spectra, such as for example analyses of the chemical composition, should be carried out with care even if the lines appear to be weak.

arXiv:1811.05991v1 [pdf, other]
Discovery of a disrupting open cluster far into the Milky Way halo: a recent star formation event in the leading arm of the Magellanic stream?
Comments: 16 pages, 9 figures, 5 tables; submitted to ApJ

We report the discovery of a young (${\rm age} \sim 130~{\rm Myr}$), low-mass ($M \sim 1200~{\rm M}_\odot$), metal-poor ($[{\rm Fe}/{\rm H}] \sim -1.1$) stellar association at a heliocentric distance $D \approx 29~{\rm kpc}$, placing it far into the Milky Way halo. At its present Galactocentric position $(R, z) \sim (23, 15)~{\rm kpc}$, the association is (on the sky) near the leading arm of the gas stream emanating from the Magellanic cloud system, but is located $\approx 60^\circ$ from the Large Magellanic Cloud (LMC) center on the other side of the Milky Way disk. If we assume that the cluster is co-located with HI gas in the stream, we directly measure the distance to the leading arm of the Magellanic stream. The measured distance is inconsistent with stream predictions from models of the LMC/SMC interaction and infall into the Milky Way that do not account for ram pressure and gas interaction with Milky Way disk. The estimated age of the cluster is consistent with the time of last passage of the leading arm gas through the Galactic midplane, and we therefore speculate that this star-formation event was triggered by its the last disk midplane passage. Most details of this idea remain a puzzle: the Magellanic stream has low column density, the Milky Way disk at this large radius has low gas density, and the relative velocity of the leading arm gas and Milky Way gas is large. However it formed, the discovery of a young stellar cluster in the Milky Way halo presents an interesting opportunity for study. This cluster was discovered with Gaia astrometry and photometry alone, but folow-up DECam photometry was crucial for measuring its properties.

arXiv:1811.05992v1 [pdf, other]
The Multiple Merger Assembly of a Hyper-luminous Obscured Quasar at redshift 4.6
Comments: To be published in Science on the 15th of November 2018

Galaxy mergers and gas accretion from the cosmic web drove the growth of galaxies and their central black holes at early epochs. We report spectroscopic imaging of a multiple merger event in the most luminous known galaxy, WISE J224607.56-052634.9 (W2246-0526), a dust-obscured quasar at redshift 4.6, 1.3 Gyr after the Big Bang. Far-infrared dust continuum observations show three galaxy companions around W2246-0526 with disturbed morphologies, connected by streams of dust likely produced by the dynamical interaction. The detection of tidal dusty bridges shows that W2246-0526 is accreting its neighbors, suggesting merger activity may be a dominant mechanism through which the most luminous galaxies simultaneously obscure and feed their central supermassive black holes.

arXiv:1811.05994v1 [pdf, other]
Probabilistic Random Forest: A machine learning algorithm for noisy datasets
Comments: Accepted by AJ, comments are welcome! Code is available at https://github.com/ireis/PRF

Machine learning (ML) algorithms become increasingly important in the analysis of astronomical data. However, since most ML algorithms are not designed to take data uncertainties into account, ML based studies are mostly restricted to data with high signal-to-noise ratio. Astronomical datasets of such high-quality are uncommon. In this work we modify the long-established Random Forest (RF) algorithm to take into account uncertainties in the measurements (i.e., features) as well as in the assigned classes (i.e., labels). To do so, the Probabilistic Random Forest (PRF) algorithm treats the features and labels as probability distribution functions, rather than deterministic quantities. We perform a variety of experiments where we inject different types of noise to a dataset, and compare the accuracy of the PRF to that of RF. The PRF outperforms RF in all cases, with a moderate increase in running time. We find an improvement in classification accuracy of up to 10% in the case of noisy features, and up to 30% in the case of noisy labels. The PRF accuracy decreased by less then 5% for a dataset with as many as 45% misclassified objects, compared to a clean dataset. Apart from improving the prediction accuracy in noisy datasets, the PRF naturally copes with missing values in the data, and outperforms RF when applied to a dataset with different noise characteristics in the training and test sets, suggesting that it can be used for Transfer Learning.

arXiv:1811.05996v1 [pdf, other]
Noodle Models for Scintillation Arcs

I show that multiple, narrow, parallel strips of phase-changing material, or "noodles," generically produce parabolic structures in the delay-rate domain. Such structures are observed as "scintillation arcs" for many less-strongly-scattered pulsars. The noodle model assumes that the strips are extremely long, with widths comparable to a pair of Fresnel zone at their separation from the origin. Their lengths are many times a Fresnel scale, or hundreds or thousands times their widths. Physically, the strips may correspond to filaments or sheets of over- or under-dense plasma, with a normal perpendicular to the line of sight. They may lie in reconnection sheets, along magnetic field lines. If so, observations of scintillation arcs would allow visualization of magnetic fields in reconnection regions. Along the strips, the Kirchhoff integral leads to a stationary-phase point where the strip is closest to the line of sight. Across the strip, the integral leads to a 1D Fourier transform to the observer plane. Most observations can measure for each strip only an amplitude, that is related to the width of the strip and its phase contrast with surrounding material, and a phase, that varies with the geometric phase where the strip is closest to the line of sight. Observations suggest a minimum strip width of about 800 km, comparable to the ion cyclotron radius.

arXiv:1811.05998v1 [pdf, other]
Thermal Emission in the Southwest Clump of VY CMa
Comments: Submitted to AJ. 14 pages, 5 figures, 2 tables

We present high spatial resolution LBTI/NOMIC $9-12$ $\mu m$ images of VY CMa and its massive outflow feature, the Southwest (SW) Clump. Combined with high-resolution imaging from HST ($0.4-1$ $\mu m$) and LBT/LMIRCam ($1-5$ $\mu m$), we isolate the spectral energy distribution (SED) of the clump from the star itself. Using radiative-transfer code DUSTY, we model both the scattered light from VY CMa and the thermal emission from the dust in the clump to estimate the optical depth, mass, and temperature of the SW Clump. The SW Clump is optically thick at 8.9 $\mu m$ with a brightness temperature of $\sim$200 K. With a dust chemistry of equal parts silicates and metallic iron, as well as assumptions on grain size distribution, we estimate a dust mass of $5.4\times10^{-5}\,M_\odot$. For a gas--to--dust ratio of 100, this implies a total mass of $5.4\times10^{-3}\,M_\odot$. Compared to the typical mass-loss rate of VY CMa, the SW Clump represents an extreme, localized mass-loss event from $\lesssim300$ years ago.

arXiv:1811.06001v1 [pdf, other]
Bounce inflation driven by Higgs field

In this work, we investigate a model of bounce inflation driven by the Higgs field. The Higgs field is non-minimally coupled with gravity through the Gauss-Bonnet term. We show that the Higgs field could drive a power-law contraction followed by a bounce and thereafter an inflationary phase with exit. The phases of contraction and inflation are obtained analytically. The smooth transition to the inflationary phase from contraction is obtained numerically. Further, the power-spectrum of the model is found to be consistent with the cosmological data.

arXiv:1811.06015v1 [pdf, other]
The "Fundamental Metallicity Relation" in CALIFA, SDSS-IV MaNGA and high-z galaxies

Metallicity of local galaxies is tightly related not only to stellar mass, i.e. the Mass-Metallicity (MZ) Relation, but also to star formation rate (SFR) through the so-called Fundamental Metallicity Relation (FMR), with more active galaxies showing lower metallicities Z at fixed mass. Interestingly, the relation does not evolve with redshift, with high-z galaxies up to z~2.5 following the same FMR defined by SDSS locally. However, FMR with different shapes have been proposed for local galaxies, and the existence of a FMR and the role of the SFR has been recently questioned by some authors, who do not confirm the dependence of the residuals of the MZ relation on SFR in their datasets, both locally and at high-z. In this paper we first discuss the different parameterisations of this M*-Z-SFR relation that appeared in the literature, to understand the origin of their different shapes. We then re-analysed data from CALIFA and SDSS-IV MaNGA surveys, which were used to suggest no dependency of metallicity on SFR in local galaxies. Contrary to those claims, we find that those datasets are instead fully consistent with the FMR predictions, with the expected dependency on SFR at fixed mass. Finally, we analysed those high-z data whose consistency with the FMR was questioned. While an internal dependency on SFR among the sub-samples is difficult to detect at high-z due to the limited dynamic range sampled in the three parameters and to the intrinsic scatter and uncertainties of such small samples, all these datasets are compatible with the FMR defined locally by SDSS galaxies, confirming the no evolution of the FMR in these data up to z~2.3

arXiv:1811.06020v1 [pdf, other]
TESS full orbital phase curve of the WASP-18b system
Comments: Submitted to AAS journals. Posted on the arXiv for comments from the community

We present the full visible-light orbital phase curve of the transiting planet WASP-18b measured by the TESS Mission. The phase curve includes the transit, secondary eclipse, and sinusoidal modulations across the orbital phase shaped by the planet's atmospheric characteristics and the star-planet gravitational interaction. We measure the beaming (Doppler boosting) and tidal ellipsoidal distortion phase modulations and show that the amplitudes of both agree with theoretical expectations. We find that the light from the planet's day side occulted during secondary eclipse, with a relative brightness of 355 $\pm$ 21 ppm, is dominated by thermal emission, leading to an upper limit on the geometric albedo in the TESS band of 0.057 (2 $\sigma$). We also detect the phase modulation due to the planet's atmosphere longitudinal brightness distribution. We find that its maximum is well-aligned with the sub-stellar point, and we place an upper limit on the phase shift of 3.5 deg (2 $\sigma$). Finally, we do not detect light from the planet's night-side hemisphere, with an upper limit of 53 ppm (2 $\sigma$), which is 15 % of the day-side brightness. The low albedo, lack of atmospheric phase shift, and inefficient heat distribution from the day to night hemispheres that we deduce from our analysis are consistent with theoretical expectations and similar findings for other strongly irradiated gas giant planets. This work demonstrates the potential of TESS data for studying full orbital phase curves of transiting systems.

arXiv:1811.06025v1 [pdf, other]
Large-Scale Diffuse Intergalactic Magnetic Fields Constraints with the Cherenkov Telescope Array
Comments: 4 pages, Proceedings of Talk presented at the IAU Focus Meeting FM8: "New Insights in Extragalactic Magnetic Fields", held at the IAU General Assembly - Vienna, 2018 August 29-31

Magnetic fields of the order of $\mu$-Gauss are observationally detected in galaxies and galaxy clusters, which can be (at least) in part originated by the amplification of much weaker primordial seed fields. These fields should be carried out by strong galactic outflows, magnetically enriching the InterGalactic Medium (IGM). However direct observation of magnetic fields in the IGM is scarce. This talk will give a review of how Intergalactic Magnetic Field (IGMF) can be constrained using gamma-ray observations. High-energy TeV photons emitted by distant blazars can interact with the cosmic extragalactic optical/infrared/microwave background light, producing electron-positron pairs, and initiating electromagnetic cascades in the IGM. The charged component of these cascades is deflected by IGMFs, thereby reducing the observed point-like TeV flux, and creating an extended image in the GeV energy range, which can potentially be detected with $\gamma$-ray telescopes (Fermi-LAT, HESS, CTA). Studies (e.g., Neronov & Vovk 2010, Dolag et al. 2011) have put lower limits on the IGMF strength of the order of $10^{-16} - 10^{-15} G$, and filling factors of $60\%$. This talk will describe the constraints which the Cherenkov Telescope Array sensitivity is expected to give (CTA Consortium 2018).

arXiv:1811.06027v1 [pdf, other]
Compton-thick AGN in the NuSTAR era II: A deep NuSTAR and XMM-Newton view of the candidate Compton thick AGN in NGC 1358

We present the combined NuSTATR and XMM-Newton 0.6-79 keV spectral analysis of a Seyfert 2 galaxy, NGC 1358, which we selected as a candidate Compton thick (CT-) active galactic nucleus (AGN) on the basis of previous Swift/BAT and Chandra studies. According to our analysis, NGC 1358 is confirmed to be a CT-AGN using physical motivated models, at >3 $\sigma$ confidence level. Our best-fit shows that the column density along the 'line-of-sight' of the obscuring material surrounding the accreting super-massive black hole is N$\rm _H$ = [1.96--2.80] $\times$ 10$^{24}$ cm$^{-2}$. The high-quality data from NuSTAR gives the best constraints on the spectral shape above $\sim$10 keV to date on NGC 1358. Moreover, by combining NuSTAR and XMM-Newton data, we find that the obscuring torus has a low covering factor ($f_c$ <0.17), and the obscuring material is distributed in clumps, rather than uniformly. We also derive an estimate of NGC 1358's Eddington ratio, finding it to be $\lambda_{\rm Edd}$ $\sim$$4.7_{-0.3}^{+0.3}$ $\times$ 10$^{-2}$, which is in acceptable agreement with previous measurements. Finally, we find no evidence of short-term variability, over a $\sim$100 ks time-span, in terms of both 'line-of-sight' column density and flux.

arXiv:1811.06028v1 [pdf, other]
The Relation Between Galaxy ISM and Circumgalactic OVI Gas Kinematics Derived from Observations and $Λ$CDM Simulations
Comments: 24 pages, 21 figures, 4 tables. Accepted to ApJ on November 14, 2018

We present the first galaxy-OVI absorption kinematic study for 20 absorption systems (EW>0.1~{\AA}) associated with isolated galaxies (0.15$<z<$0.55) that have accurate redshifts and rotation curves obtained using Keck/ESI. Our sample is split into two azimuthal angle bins: major axis ($\Phi<25^{\circ}$) and minor axis ($\Phi>33^{\circ}$). OVI absorption along the galaxy major axis is not correlated with galaxy rotation kinematics, with only 1/10 systems that could be explained with rotation/accretion models. This is in contrast to co-rotation commonly observed for MgII absorption. OVI along the minor axis could be modeled by accelerating outflows but only for small opening angles, while the majority of the OVI is decelerating. Along both axes, stacked OVI profiles reside at the galaxy systemic velocity with the absorption kinematics spanning the entire dynamical range of their galaxies. The OVI found in AMR cosmological simulations exists within filaments and in halos of ~50 kpc surrounding galaxies. Simulations show that major axis OVI gas inflows along filaments and decelerates as it approaches the galaxy while increasing in its level of co-rotation. Minor axis outflows in the simulations are effective within 50-75 kpc beyond that they decelerate and fall back onto the galaxy. Although the simulations show clear OVI kinematic signatures they are not directly comparable to observations. When we compare kinematic signatures integrated through the entire simulated galaxy halo we find that these signatures are washed out due to full velocity distribution of OVI throughout the halo. We conclude that OVI alone does not serve as a useful kinematic indicator of gas accretion, outflows or star-formation and likely best probes the halo virial temperature.

arXiv:1811.06053v1 [pdf, other]
The case for gravitational millilensing in the multiply--imaged quasar B1152+199
Comments: 9 pages, 4 figures, submitted to MNRAS

Previous Very Long Baseline Interferometry (VLBI) observations of the quasar B1152+199 at 5GHz has revealed two images of a strongly lensed jet with seemingly discordant morphologies. Whereas the jet appears straight in one of the images, the other exhibits slight curvature on milliarcsecond scales. This is unexpected from the lensing solution and has been interpreted as possible evidence for secondary, small-scale lensing (millilensing) by a compact object with a mass of $~10^5$-$10^7\ M_\odot$ located close to the curved image. The probability for such a superposition is extremely low unless the millilens population has very high surface number density. Here, we revisit the case for millilensing in B1152+199 by combining new global-VLBI data at 8.4GHz with two datasets from the European VLBI Network (EVN) at 5GHz (archival) and at 22GHz (new dataset), and the previously published 5GHz Very Long Baseline Array (VLBA) data. We find that the new data with a more circular synthesized beam, exhibits no apparent milliarcsecond-scale curvature in image B. Various observations of the object spanning $\sim$15 years apart enable us to improve the constraints on lens system (thanks also to the improved astrometry resulting from 22GHz observations) to the point that the only plausible explanation left for the apparent curvature is the artifact due to the shape of the synthesized beam.

arXiv:1811.06056v1 [pdf, other]
The Efficiency of Noble Gas Trapping in Astrophysical Environments

Amorphous ice has long been invoked as a means for trapping extreme volatiles into solids, explaining the abundances of these species in comets and planetary atmospheres. Experiments have shown that such trapping is possible and have been used to estimate the abundances of each species in primitive ices after they formed. However, these experiments have been carried out at deposition rates which exceed those expected in a molecular cloud or solar nebula by many orders of magnitude. Here we develop a numerical model which reproduces the experimental results and apply it to those conditions expected in molecular clouds and protoplanetary disks. We find that two regimes of ice trapping exist: 'burial trapping' where the ratio of trapped species to water in the ice reflects that same ratio in the gas and 'equilibrium trapping' where the ratio in the ice depends only on the partial pressure of the trapped species in the gas. The boundary between these two regimes is set by both the temperature and rate of ice deposition. Such effects must be accounted for when determining the source of trapped volatiles during planet formation.

arXiv:1811.06061v1 [pdf, other]
G337.342-0.119 (the "Pebble"): A Cold, Dense, High-Mass Molecular Cloud with Unusually Large Linewidths and a Candidate High-Mass Star Cluster Progenitor

Exactly how high-mass star clusters form, especially the young massive clusters (YMCs: age $<100$ Myr; mass $>10^4$ solar masses), remains an open problem, largely because they are so rare that examples of their cold, dense, molecuar progenitors remain elusive. The molecular cloud G337.342$-$0.119, the 'Pebble,' is a candidate for such a cold progenitor. Although G337.342$-$0.119, was originally identified as four separate ATLASGAL clumps, the similarity in their molecular line velocities and linewidths in the MALT90 dataset demonstrate that these four clumps are in fact one single, coherent cloud. This cloud is unique in the MALT90 survey for its combination of both cold temperatures ($T_{dust} \sim 14$ K) and large linewidths $(\Delta V \sim 10$ km s$^{-1}$). The near/far kinematic distance ambiguity is difficult to resolve for \Pebble. At the near kinematic distance (4.7 kpc), the mass is 5,000 \Msun\, and the size is $7\times2$ pc. At the far kinematic distance (11 kpc), the mass is 27,000 \Msun\, and the size is $15 \times 4$ pc. The unusually large linewidths of G337.342$-$0.119,are difficult to reconcile with a gravitationally bound system in equilibrium. If our current understanding of the Galaxy's Long Bar is approximately correct, G337.342$-$0.119, cannot be located at its end. Rather, it is associated with a large star-forming complex that contains multiple clumps with large linewidths. If G337.342$-$0.119, is a prototypical cold progenitor for a high-mass cluster, its properties may indicate that the onset of high-mass star cluster formation is dominated by extreme turbulence. , is a prototypical cold progenitor for a high-mass cluster, its properties may indicate that the onset of high-mass star cluster formation is dominated by extreme turbulence.

arXiv:1811.06081v1 [pdf, other]
Measurement of the Splashback Feature around SZ-selected Galaxy Clusters with DES, SPT and ACT
Comments: 17 pages, 12 figures, to be submitted to MNRAS

We present a detection of the splashback feature around galaxy clusters selected using their Sunyaev-Zel'dovich (SZ) signal. Recent measurements of the splashback feature around optically selected galaxy clusters have found that the splashback radius, $r_{\rm sp}$, is smaller than predicted by N-body simulations. A possible explanation for this discrepancy is that $r_{\rm sp}$ inferred from the observed radial distribution of galaxies is affected by selection effects related to the optical cluster-finding algorithms. We test this possibility by measuring the splashback feature in clusters selected via the SZ effect in data from the South Pole Telescope SZ survey and the Atacama Cosmology Telescope Polarimeter survey. The measurement is accomplished by correlating these clusters with galaxies detected in the Dark Energy Survey Year 3 data. The SZ observable used to select clusters in this analysis is expected to have a tighter correlation with halo mass and to be more immune to projection effects and aperture-induced biases than optically selected clusters. We find that the measured $r_{\rm sp}$ for SZ-selected clusters is consistent with the expectations from simulations, although the small number of SZ-selected clusters makes a precise comparison difficult. In agreement with previous work, when using optically selected redMaPPer clusters, $r_{\rm sp}$ is $\sim$ $2\sigma$ smaller than in the simulations. These results motivate detailed investigations of selection biases in optically selected cluster catalogs and exploration of the splashback feature around larger samples of SZ-selected clusters. Additionally, we investigate trends in the galaxy profile and splashback feature as a function of galaxy color, finding that blue galaxies have profiles close to a power law with no discernible splashback feature, which is consistent with them being on their first infall into the cluster.

arXiv:1811.06089v1 [pdf, other]
A Tale of Two Scales: Screening in Large Scale Structure
Comments: 4 pages, 1 figure, submitted to the Proceedings of the 43rd "Rencontres de Moriond"

The perturbative treatment of dark matter in structure formation relies on the existence of a well-defined expansion parameter, $k/k_{\rm NL}$, with $k_{\rm NL}$ signalling the onset and ultimately the leading role of non-linearities in the system. Cosmologies beyond the {\Lambda}CDM model often come with additional degree(s) of freedom. The scale $k_{\rm V}$ at which non-linearities become important in the additional sector(s) can be rather different from $k_{\rm NL}$. For theories endowed with a Vainshtein-type screening mechanism, $k_{\rm V}$ sets the scale where screening becomes efficient and restores continuity with the predictions of general relativity. This is precisely the dynamics that allows such theories to pass existing observational tests at scales where general relativity has been tested with exquisite precision (e.g. solar system scales). We consider here the mildly-non-linear scales of a dark matter component coupled to a galileon-type field and focus in particular on the case of a $k_{\rm V}$ < $k_{\rm NL}$ hierarchy. We put forward a phenomenological framework that describes the effects of screening dynamics on large scale structure observables.

arXiv:1811.06124v1 [pdf, other]
The C-Band All-Sky Survey (C-BASS): Digital backend for the northern survey

The C-Band All-Sky Survey (C-BASS) is an all-sky full-polarization survey at a frequency of 5 GHz, designed to provide data complementary to the all-sky surveys of WMAP and Planck and future CMB B-mode polarization imaging surveys. We describe the design and performance of the digital backend used for the northern part of the survey. In particular we describe the features that efficiently implement the demodulation and filtering required to suppress contaminating signals in the time-ordered data, and the capability for real-time correction of detector non-linearity and receiver balance.

arXiv:1811.06148v1 [pdf, other]
A numerical twist on the observational spin parameter, $λ_R$
Comments: Accepted for publication in MNRAS. 15 pages, 14 figures

A primary goal of integral field spectroscopic (IFS) surveys is to provide a statistical census of galaxies classified by their internal kinematics. As a result, the observational spin parameter, $\lambda_R$, has become one of the most popular methods of quantifying the relative importance of velocity dispersion and rotation in supporting a galaxy's inner structure. The goal of this paper is to examine the relationship between the observationally deduced $\lambda_R$ and one of the most commonly used theoretical spin parameters in the literature, the Bullock et al. (2001) $\lambda'$. Using a set of $N$-body realisations of galaxies from which we construct mock IFS observations, we measure $\lambda_R$ as an observer would, incorporating the effects of beam smearing and seeing conditions. Assuming parameters typical of current IFS surveys, we confirm that there are strong positive correlations between $\lambda_R$ and measurement radius, and strong negative correlations between $\lambda_R$ and size of the PSF, for late-type galaxies; these biases can be reduced using a recently proposed empirical correction. Once observational biases are corrected for, we find that $\lambda_R$ provides a good approximation to $\sim \sqrt{3}/2 \; \lambda'(\rm R_{\rm eff})$, where $\lambda'$ is evaluated for the galactic stellar component within 1 R$_{\rm eff}$.

arXiv:1811.06214v1 [pdf, other]
Topological model of the anemone microflares in the solar chromosphere
Comments: LaTeX, aa documentclass, 4 pages, 4 EPS figures, submitted to Astronomy & Astrophysics

The chromospheric anemone microflares, which were discovered by Hinode satellite about a decade ago, are the specific transient phenomena starting from a few luminous ribbons on the chromospheric surface and followed by the eruption upwards. While the eruptive stage was studied in sufficient detail, a quantitative theory of formation of the initial multi-ribbon structure remains undeveloped till now. Here, we construct a sufficiently simple but general model of the magnetic field sources that is able to reproduce all the observed types of the luminous ribbons by varying only a single parameter. As a working tool, we employ the Gorbachev-Kel'ner-Somov-Shvarts (GKSS) model of the magnetic field, which was originally suggested about three decades ago to explain fast ignition of the magnetic reconnection over considerable spatial scales by tiny displacements of the magnetic sources. Quite unexpectedly, this model turns out to be efficient also for the description of generic multi-ribbon structure in the anemone flares. As follows from our numerical simulation, displacement of a single magnetic source (sunspot) with respect to three other sources results in a complex transformation from three to four ribbons and, then, again to three ribbons but with an absolutely different arrangement. Such structures closely remind the observed patterns of emission in the anemone microflares.

arXiv:1811.06240v1 [pdf, other]
Probing accretion of ambient cloud material into the Taurus B211/B213 filament
Comments: 16 pages, 17 figures, accepted in A&A

Herschel observations have emphasized the role of molecular filaments in star formation. However, the origin and evolution of these filaments are not yet well understood, partly because of the lack of kinematic information. To examine whether the B211/B213 filament is accreting background gas due to its gravitational potential, we produced a toy accretion model and compared its predictions to the 12CO(1--0) and 13CO(1--0) velocity patterns. We also examined the spatial distributions of Halpha, 857 GHz continuum, and HI emission to search for evidence of large-scale external effects. We estimated the depth of the cloud around the B211/B213 filament to be 0.3--0.7 pc under the assumption that the density of the gas is the same as the 13CO critical density. Compared to a linear extent of >10 pc in the plane of the sky, this suggests that the 3D morphology of the cloud is sheet-like. 12CO and 13CO PV diagrams perpendicular to the filament axis show that the emission from the gas surrounding B211/B213 is redshifted to the northeast of the filament and blueshifted to the southwest, respectively, and that the velocities of both components approach the filament velocity as the line of sight approaches the filament crest. The PV diagrams predicted by our accretion model are in good agreement with the observed 12CO and 13CO PV diagrams, supporting the scenario of mass accretion into the filament proposed by Palmeirim et al. Moreover, inspection of the distribution of the Halpha and 857 GHz emission in the Taurus-California-Perseus region suggests that the B211/B213 filament may have formed as a result of an expanding supershell generated by the Per OB2 association. Based on these results, we propose a scenario in which the B211/B213 filament was initially formed by large-scale compression of HI gas and then is now growing in mass due to the gravitational accretion of ambient cloud molecular gas.

arXiv:1811.06243v1 [pdf, other]
Study of variable stars associated with maser sources: G025.65+1.05
Comments: Accepted for publication in RAA

We report variation of K-band infrared (IR) emission in the vicinity of the G025.65+1.05 water and methanol maser source. New observational data were obtained with 2.5m telescope of the Caucasian Mountain Observatory (CMO) of Moscow State University on 2017-09-21 during the strong water maser flare. We found that the IR source situated close to the maser position had decreased brightness in comparison to archive data. This source is associated with a massive young stellar object (MYSO) corresponding to the compact infrared source IRAS 18316-0602 (RAFGL 7009S). Similar decrease in K-brightness of the IR source close to the maser position was observed in March~2011 when the water maser activity was increased. The dips in MYSO brightness can be related to the maser flare phases. Maser flares that are concurrent with dips of the IR emission can be explained if the lower IR radiation field enables more efficient sink of the pumping cycle by allowing IR photons to escape the maser region.

arXiv:1811.06251v1 [pdf, other]
Investigating ULX accretion flows and cyclotron resonance in NGC 300 ULX1
Comments: 16 pages, 10 figures, accepted for publication in Astronomy & Astrophysics

Methods. We analyzed broadband XMM-Newton and NuSTAR observations of NGC 300 ULX1, performing phase-averaged and phase-resolved spectroscopy. We compared two physically motivated models for the source spectrum: Non-thermal accretion column emission modeled by a power law with high-energy exponential roll-off (AC model) vs multicolor thermal emission from an optically thick accretion envelope plus a hard power-law tail (MCAE model). We combine the findings of our Bayesian analysis with qualitative physical considerations to evaluate the suitability of each model. Results. The low-energy part (<2 keV) of the source spectrum is dominated by non-pulsating, multicolor thermal emission. The (pulsating) high energy continuum is more ambiguous. If modelled with the AC model a residual structure is detected, that can be modeled using a broad Gaussian absorption line centered at ~12 keV. However, the same residuals can be successfully modeled using the MCAE model, without the need for the absorption-like feature. Model comparison, using the Bayesian approach strongly indicates that the MCAE model -- without the absorption line -- is the preferred model. Conclusions. All models considered strongly indicate the presence of an accretion disk truncated at a large distance from the central object, as has been recently suggested for a large fraction of both pulsating and non-pulsating ULXs. The hard, pulsed emission is not described by a smooth spectral continuum. If modelled by a broad Gaussian absorption line, the fit residuals can be interpreted as a cyclotron scattering feature (CRSF) compatible with a ~10^12 G magnetic field. However, the MCAE model describes the spectral and temporal characteristics of the source emission, without the need for an absorption feature and yields physically meaningful parameter values. Therefore strong doubts are cast on the presence of a CRSF in NGC 300 ULX1.

arXiv:1811.06266v1 [pdf, other]
Faraday rotation study of NGC 612 (PKS 0131-36): a hybrid radio source and its magnetised circumgalactic environment
Comments: 9 pages, 7 figures. Accepted for publication in MNRAS

We present a polarization and Faraday rotation study of the hybrid morphology radio galaxy NGC 612 (PKS 0131-36), using Australian Telescope Compact Array observations from 1 to 3 GHz. In general, the results are consistent with an external Faraday screen close to the radio source. In the eastern FRII lobe, the RM of the hotspot increases in magnitude towards the leading edge, as well as changing sign (compared to the rest of the lobe). The Faraday depolarization is also ~3 times larger at the hotspot than elsewhere. A plausible explanation for this is significant compression of ambient magnetised gas by the bow shock produced by the advancing hotspot. The western FRI lobe also exhibits some evidence of interaction with local magnetised gas, as a transverse band of high RM coincides with a distinct bend in the lobe. Previous observations of NGC 612 revealed an HI bridge of tidal debris along the direction of the eastern lobe towards the gas-rich companion NGC 619. We find no clear evidence that ionised gas associated with this bridge is either mixing with or lies in the foreground of the radio source. This is consistent with the absence of HI absorption against the hotspot, and indicates that the tidal debris must lie mostly behind the eastern lobe.

arXiv:1811.06291v1 [pdf, other]
The High Mass X-ray Binaries in star-forming galaxies
Comments: 4 pages, 2 figures. To appear in Proc. IAUS 346: High-mass X-ray binaries: illuminating the passage from massive binaries to merging compact objects

The high mass X-ray binaries (HMXBs) provide an exciting framework to investigate the evolution of massive stars and the processes behind binary evolution. HMXBs have shown to be good tracers of recent star formation in galaxies and might be important feedback sources at early stages of the Universe. Furthermore, HMXBs are likely the progenitors of gravitational wave sources (BH--BH or BH--NS binaries that may merge producing gravitational waves). In this work, we investigate the nature and properties of HMXB population in star-forming galaxies. We combine the results from the population synthesis model MOBSE (Giacobbo et al. 2018) together with galaxy catalogs from EAGLE simulation (Schaye et al. 2015). Therefore, this method describes the HMXBs within their host galaxies in a self-consistent way. We compute the X-ray luminosity function (XLF) of HMXBs in star-forming galaxies, showing that this methodology matches the main features of the observed XLF.

arXiv:1811.06302v1 [pdf, other]
Supermassive Black Holes with High Accretion Rates in Active Galactic Nuclei. VIII. Structure of the Broad-Line Region and Mass of the Central Black Hole in Mrk 142
Comments: 21 pages, 12 figures, 5 tables; ApJ accepted; The software BRAINS available at https://github.com/LiyrAstroph/BRAINS

This is the eighth in a series of papers reporting on a large reverberation mapping campaign to measure black hole (BH) mass in high accretion rate active galactic nuclei (AGNs). We employ the recently developed dynamical modeling approach for broad-line regions (BLRs) based on the method of Pancoast et al. to analyze the reverberation mapping dataset of Mrk 142 observed in the first monitoring season. In this approach, continuum variations are reconstructed using a damped random walk process, and BLR structure is delineated using a flexible disk-like geometry, in which BLR clouds move around the central BH with Keplerian orbits or inflow/outflow motion. The approach also includes the possibilities of anisotropic emission of BLR clouds, non-linear response of the line emission to the continuum, and different long-term trends in the continuum and emission-line variations. We implement the approach in a Bayesian framework that is apt for parallel computation and use a Markov Chain Monte Carlo technique to recover the parameters and uncertainties for the modeling, including mass of the central BH. We apply three BLR models with different prescriptions of BLR clouds distributions and find that the best model for fitting the data of Mrk 142 is a two-zone BLR model, consistent with the theoretical BLR model surrounding slim accretion disks. The best model yields a BH mass of $\log (M_\bullet/M_\odot)=6.23_{-0.45}^{+0.26}$, resulting in a virial factor of $\log f=-0.36_{-0.54}^{+0.33}$ for the full width at half maximum of the H$\beta$ line measured from the mean spectrum. The virial factors for the other measures of the H$\beta$ line width are also presented.

arXiv:1811.06307v1 [pdf, other]
PoWR grids of non-LTE model atmospheres for OB-type stars of various metallicities
Comments: 12 pages, 14 figures, accepted for publication in Astronomy & Astrophysics

The study of massive stars in different metallicity environments is a central topic of current stellar research. The spectral analysis of massive stars requires adequate model atmospheres. The computation of such models is difficult and time-consuming. Therefore, spectral analyses are greatly facilitated if they can refer to existing grids of models. Here we provide grids of model atmospheres for OB-type stars at metallicities corresponding to the Small and Large Magellanic Clouds, as well as to solar metallicity. In total, the grids comprise 785 individual models. The models were calculated using the state-of-the-art Potsdam Wolf-Rayet (PoWR) model atmosphere code. The parameter domain of the grids was set up using stellar evolution tracks. For all these models, we provide normalized and flux-calibrated spectra, spectral energy distributions, feedback parameters such as ionizing photons, Zanstra temperatures, and photometric magnitudes. The atmospheric structures (the density and temperature stratification) are available as well. All these data are publicly accessible through the PoWR website.

arXiv:1811.06313v1 [pdf, other]
Life Before Fermi - Back to the Solar System
Comments: Accepted for publication in the Journal of the British Interplanetary Society

The existence of intelligent, interstellar traveling and colonising life is a key assumption behind the Fermi Paradox. Until recently, detecting signs of life elsewhere has been so technically challenging as to seem almost impossible. However, new observational insights and other developments mean that signs of life elsewhere might realistically be uncovered in the next decade or two. We here review what are believed to be the basic requirements for life, the history of life on Earth, and then apply this knowledge to potential sites for life in our own Solar System. We conclude that the necessities of life - liquid water and sources of energy - are in fact quite common in the Solar System, but most potential sites are beneath the icy surfaces of gas giant moons. If this is the case elsewhere in the Galaxy, life may be quite common but, even if intelligence develops, is essentially sealed in a finite environment, unable to communicate with the outside world.

arXiv:1811.06317v1 [pdf, other]
The physics of asymmetric supernovae and supernovae remnants
Comments: 48 pages and 31 low quality figures

We model the circumstellar medium with four density profiles: hyperbolic type, power law type, exponential type and Gaussian type. We solve analytically or numerically the four first-order differential equations which arise in the framework of the classical thin layer approximation. The non-cubic dependence of the swept mass with the advancing radius is also considered. We derive the equation of motion for the thin layer approximation in special relativity in two cases. The initial conditions are chosen in order to model the temporal evolution of SN 1987A over 23 years and of SN 1006 over 1000 years. We review the building blocks of the symmetrical and asymmetrical formations of the image.

arXiv:1811.06333v1 [pdf, other]
The Dynamics of OB Associations
Comments: 7 pages; in Proceedings of The 20th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, ed. S. Wolk

The formation and evolution of young star clusters and OB associations is fundamental to our understanding of the star formation process, the conditions faced by young binary and planetary systems, and the formation of long-lived open and globular clusters. Despite this our understanding of the physical processes that drive this evolution has been limited by the static nature of most observations. This is all changing thanks to a revolution in kinematic data quality from large-scale radial velocity surveys and new astrometric facilities such as Gaia. Here I summarise recent studies of multiple OB associations from both {\it Gaia} and ground-based astrometric surveys. These observations show that OB associations have considerable kinematic substructure and no evidence for the radial expansion pattern predicted by theories such as residual gas expulsion. This means that, contrary to the standard view of OB associations as expanded star clusters, these systems could never have been dense star clusters in the past and were most likely born as extended and highly substructured groups of stars. This places strong constraints on the primordial clustering of young stars and the conditions faced by young planetary systems.

arXiv:1811.06335v1 [pdf, other]
Do sub-galactic regions follow the galaxy-wide X-ray scaling relations? The example of NGC 3310 and NGC 2276
Comments: 25 pages, 15 figures, 12 tables. Accepted for publication in MNRAS

We present results from Chandra observations of the X-ray starburst galaxies NGC 3310 and NGC 2276. We detect 27 discrete sources in NGC 3310, and 19 discrete sources in NGC 2276 with luminosities above $\mathrm{1.0\times 10^{38}\ erg\ s^{-1}}$. The majority of the sources have photon indices of 1.7-2.0, typical for X-ray binaries. Both galaxies have large numbers of ultra-luminous X-ray sources (ULXs; sources with $\mathrm{L(0.3-10.0\ keV)>10^{39}\ erg\ s^{-1}}$), 14 for NGC 3310 concentrated on the circumnuclear star-forming ring and north spiral arm and 11 for NGC 2276 with the brighter ones on the west side of the galaxy which is compressed due to harassment by the intra-group medium it is moving into. We find for both galaxies that the ULX-hosting areas are located above the general Lx-SFR scaling relations while other areas either follow or fall below the scaling relations. This indicates that sub-galactic regions follow the galaxy-wide scaling relations but with much larger scatter resulting from the age (and possibly metallicity) of their local stellar populations in agreement with recent theoretical and observational results. Such differences in age could be the origin of the scatter we observe in the low SFR regime in the Lx-SFR scaling relations.

arXiv:1811.06354v1 [pdf, other]
Evolution of star-planet systems under magnetic braking and tidal interaction
Comments: Accepted for publication in Astronomy & Astrophysics

With the discovery over the last two decades of a large diversity of exoplanetary systems, it is now of prime importance to characterize star-planet interactions and how such systems evolve. We address this question by studying systems formed by a solar-like star and a close-in planet. We focus on the stellar wind spinning down the star along its main sequence phase and tidal interaction causing orbital evolution of the systems. Despite recent significant advances in these fields, all current models use parametric descriptions to study at least one of these effects. Our objective is to introduce simultaneously ab-initio prescriptions of the tidal and braking torques, so as to improve our understanding of the underlying physics. We develop a 1D numerical model of coplanar circular star-planet systems taking into account stellar structural changes, wind braking and tidal interaction and implement it in a code called ESPEM. We follow the secular evolution of the stellar rotation assuming a bi-layer internal structure, and of the semi-major axis of the orbit. After comparing our predictions to recent observations and models, we perform tests to emphasize the contribution of ab-initio prescriptions. Our secular model of stellar wind braking reproduces well the recent observations of stellar rotation in open clusters. Our results show that a planet can affect the rotation of its host star and that the resulting spin-up or spin-down depends on the orbital semi-major axis and on the joint influence of magnetic and tidal effects. The ab-initio prescription for tidal dissipation that we used predicts fast outward migration of massive planet orbiting fast-rotating young stars. Finally, we provide the reader with a criterion based on the system's characteristics that allows us to assess whether or not the planet will undergo orbital decay due to tidal interaction.

arXiv:1811.06356v1 [pdf, other]
Self-consistent model of extragalactic neutrino flux from evolving blazar population

We study constraints on the population of neutrino emitting blazars imposed by the absence of doublets in astrophysical muon neutrino signal and z>0.3 redshift of nearest identified neutrino-emitting blazar (an order of magnitude further away than the nearest gamma-ray emitting blazar). We show that in spite of the absence of correlation of neutrino arrival directions with positions of gamma-ray emitting blazars, cumulative blazar flux could explain most of astrophysical neutrino flux measured in muon neutrino channel. This is possible if the population of neutrino emitting blazars has experienced rapid positive evolution at least as (1+z)^5 at z< 1. Such a model avoids previously derived constraint on the low level of blazar contribution to extragalactic neutrino flux because gamma-ray and neutrino fluxes are dominated by different sets of blazars. Rapid evolution of neutrino emitting blazars could be explained by the fact that only high luminosity blazars hosting radiatively efficient accretion flows are efficient neutrino sources.

arXiv:1811.06373v1 [pdf, other]
Fast error-controlling MOID computation for confocal elliptic orbits
Comments: 16 pages, 3 figures, 1 table; revised version submitted to Astronomy & Computing; the computing code is available for download at http://sourceforge.net/projects/distlink/

We present an algorithm to compute the minimum orbital intersection distance (MOID), or global minimum of the distance between the points lying on two Keplerian ellipses. This is achieved by finding all stationary points of the distance function, based on solving an algebraic polynomial equation of $16$th degree. The algorithm tracks numerical errors appearing on the way, and treats carefully nearly degenerate cases, including practical cases with almost circular and almost coplanar orbits. Benchmarks confirm its high numeric reliability and accuracy, and that regardless of its error--controlling overheads, this algorithm pretends to be one of the fastest MOID computation methods available to date, so it may be useful in processing large catalogs.

arXiv:1811.06374v1 [pdf, other]
Morpho-Photometric Redshifts

Machine learning (ML) is a standard approach for estimating the redshifts of galaxies when only photometric information is available. ML photo-z solutions have traditionally ignored the morphological information available in galaxy images or partly included it in the form of hand-crafted features, with mixed results. We train a morphology-aware photometric redshift machine using modern deep learning tools. It uses a custom architecture that jointly trains on galaxy fluxes, colors and images. Galaxy-integrated quantities are fed to a Multi-Layer Perceptron (MLP) branch while images are fed to a convolutional (convnet) branch that can learn relevant morphological features. This split MLP-convnet architecture, which aims to disentangle strong photometric features from comparatively weak morphological ones, proves important for strong performance: a regular convnet-only architecture, while exposed to all available photometric information in images, delivers comparatively poor performance. We present a cross-validated MLP-convnet model trained on 130,000 SDSS-DR12 galaxies that outperforms a hyperoptimized Gradient Boosting solution (hyperopt+XGBoost), as well as the equivalent MLP-only architecture, on the redshift bias metric. The 4-fold cross-validated MLP-convnet model achieves a bias $\delta z / (1+z) =-0.70 \pm 1 \times 10^{-3}$, approaching the performance of a reference ANNZ2 ensemble of 100 distinct models trained on a comparable dataset. The relative performance of the morphology-aware and morphology-blind models indicates that galaxy morphology does improve photometric redshift estimation.

arXiv:1811.06391v1 [pdf, other]
On the high-energy emissions of compact objects observed with INTEGRAL SPI: Event selection impact on source spectra and scientific results for the bright sources Crab Nebula, GS2023+338 and MAXI J1820+070

The INTEGRAL SPI instrument observes the hard X-ray sky from 20 keV up to a few MeV since more than 15 years. In this energy domain, the main emitters are compact objects for which SPI provides spectral information of prime interest. Recently, two transient sources reached very unusual flux levels and have been detected up to a few hundreds of keV with a high significance level. A drastic reduction of the systematic errors is thus required to obtain reliable spectra. This objective is achieved through an analysis including a detailed understanding of the instrument behavior. This paper presents both aspects of the data analysis: we first give a basic description of the instrumental issues, then we present the solution to be implemented in the SPI data analysis (at the event selection stage) and illustrate with a few examples the reliability of the SPI results in the high-energy domain when the data analysis is performed properly. We take benefit from this refined analysis procedure to propose an updated model of the hard X-ray spectral shape of the Crab Nebula. We revisit the high-energy emission observed in GS2023+338 spectra during its 2015 outburst and present the first results from the SPI observations dedicated to the recently discovered transient MAXI J1820+070.

arXiv:1811.06404v1 [pdf, other]
A high space density of L* Active Galactic Nuclei at z~4 in the COSMOS field
Comments: 10 pages, 3 figures, accepted for publication by ApJ

Identifying the source population of ionizing radiation, responsible for the reionization of the universe, is currently a hotly debated subject with conflicting results. Studies of faint, high-redshift star-forming galaxies, in most cases, fail to detect enough escaping ionizing radiation to sustain the process. Recently, the capacity of bright quasi-stellar objects to ionize their surrounding medium has been confirmed also for faint active galactic nuclei (AGNs), which were found to display an escaping fraction of ~74% at z~4. Such levels of escaping radiation could sustain the required UV background, given the number density of faint AGNs is adequate. Thus, it is mandatory to accurately measure the luminosity function of faint AGNs (L~L*) in the same redshift range. For this reason we have conducted a spectroscopic survey, using the wide field spectrograph IMACS at the 6.5m Baade Telescope, to determine the nature of our sample of faint AGN candidates in the COSMOS field. This sample was assembled using photometric redshifts, color, and X-ray information. We ended up with 16 spectroscopically confirmed AGNs at 3.6<z<4.2 down to a magnitude of i$_{AB}$=23.0 for an area of 1.73 deg$^{2}$. This leads to an AGN space density of ~1.6$\times10^{-6} Mpc^{-3}$ (corrected) at z~4 for an absolute magnitude of M$_{1450}$=-23.5. This is higher than previous measurements and seems to indicate that AGNs could make a substantial contribution to the ionizing background at z~4. Assuming that AGN physical parameters remain unchanged at higher redshifts and fainter luminosities, these sources could be regarded as the main drivers of cosmic reionization.

arXiv:1811.06408v1 [pdf, other]
SDSS-IV MaNGA: Signatures of halo assembly in kinematically misaligned galaxies
Comments: 19 pages, 12 figures. Accepted in MNRAS

We investigate the relationship of kinematically misaligned galaxies with their large-scale environment, in the context of halo assembly bias. According to numerical simulations, halo age at fixed halo mass is intrinsically linked to the large-scale tidal environment created by the cosmic web. We investigate the relationship between distances to various cosmic web features and present-time gas accretion rate. We select a sub-sample of ~900 central galaxies from the MaNGA survey with defined global position angles (PA; angle at which velocity change is greatest) for their stellar and H$\alpha$ gas components up to a minimum of 1.5 effective radii ($R_e$). We split the sample by misalignment between the gas and stars as defined by the difference in their PA. For each central galaxy we find its distance to nodes and filaments within the cosmic web, and estimate the host halo's age using the central stellar mass to total halo mass ratio $M_{*}/M_{h}$. We also construct halo occupation distributions using a background subtraction technique for galaxy groups split using the central galaxy's kinematic misalignment. We find, at fixed halo mass, no statistical difference in these properties between our kinematically aligned and misaligned galaxies. We suggest that the lack of correlation could be indicative of cooling flows from the hot halo playing a far larger role than 'cold mode' accretion from the cosmic web or a demonstration that the spatial extent of current large-scale integral field unit (IFU) surveys hold little information about large-scale environment extractable through this method.

arXiv:1811.06422v1 [pdf, other]
A Two Population Electron Synchrotron Model For Knots of Extended Jets
Comments: 14 pages, 6 figures, to appear in Astroparticle Physics

Radio observations by ALMA and upper limits on gamma ray flux by Fermi LAT have ruled out inverse Compton scattering of Cosmic Microwave Background radiation by relativistic electrons (IC/CMB) as the origin of X-ray emission from extended jets of six quasars 3C 273, PKS 0637-752, PKS 1136-135, PKS 1229-021, PKS 1354+195, and PKS 2209+080. Here we consider two populations of accelerated electrons in each knot of the extended jets to explain the radio to optical and the X-ray emission by synchrotron cooling of relativistic electrons. In all cases the jet power required is lower than the Eddington's luminosity and the observed knot emissions are well explained in this scenario.

arXiv:1811.06427v1 [pdf, other]
GD-1: the relic of an old metal-poor globular cluster
Comments: 21 pages, 16 figures, 8 tables

Combining data from Gaia DR2, SDSS DR14 and LAMOST DR6, we update the fit to model of the properties of the stellar stream GD-1 and find that it has an age of $\sim 13$ Gyr, [Fe/H] of $-2.2\pm 0.12$, and a distance from the sun of $\sim 8$ kpc. We tabulate 6D phase-space fiducial points along the GD-1 stream orbit over a 90$^\circ$ arc. The fitted orbit shows that the stream has an eccentricity $e \sim 0.3$, perigalacticon of 14.2 kpc, apogalacticon of 27.0 kpc and inclination $i \sim 40^{\circ}$. There is evidence along the arc for 4 candidate stellar overdensities, one candidate gap, two candidate stellar underdensities and is cut off at $\phi_1 \sim 2^{\circ}$ (in the stream-aligned $(\phi_1,\phi_2)$ coordinate system of \citet{kop10}). The spur originating at $\phi_1 \sim -40^{\circ}$ implies stars were pulled away from the stream trace by an encounter (potentially a dark matter subhalo). The narrowest place ( FWHM $\sim 44.6$ pc) of the GD-1 trace is at $(\phi_1, \phi_2^c) \sim (-14^{\circ}, 0.15^{\circ})$, which is $\sim (178.18^{\circ}, 52.19^{\circ})$ in (R. A., Decl.), where the progenitor is possibly located. We also find six BHB and 10 BS spectroscopic stars in the GD-1 stream.

arXiv:1811.06429v1 [pdf, other]
Discovery of Tidal RR LYRAE stars in the Bulge Globular Cluster M 62
Comments: 8 pages, 5 figures, accepted for publication in ApJ Letters

The RR Lyrae (RRL) rich globular cluster M 62 (NGC 6266) is one of the most massive globular clusters in the Milky Way, located in the dense region of the Galactic bulge, where dynamical processes that affect the survival of globular clusters are maximised. Using Gaia DR2 data we have found clear evidence for an excess of RRLs beyond the cluster tidal radius of M 62, associated partly with stars stripped into the Galaxy field. This is confirmed with new VVVX survey observations, that discard any differential reddening effect as the possible cause of the observed RRL density excess. We also determined the orbit of M 62 using accurate new measurements of its distance, radial velocity and proper motions (PMs), finding that its orbit is prograde respect to the direction of the Galactic rotation. Orbits are integrated in the non-axisymmetric galactic model \texttt{GravPot16}, which includes the perturbations due to the central Galactic bar. M 62 shows a particular orbital behaviour, having a dynamical signature of the bar-bulge region. The small extra-tidal RRLs extensions observed are roughly aligned towards the galactic center and the direction almost perpendicular to the galactic plane and not with its motion along its orbit, which may be a clear sign of bulge-crossing shocks, during the last passage close of the cluster towards its perigalacticon. M 62 would be the first clear observed case of bulge shocking in the inner Galaxy acting on a globular cluster.

arXiv:1811.06436v1 [pdf, other]
Deep Chandra Observations of ESO 428-G014: IV. The Morphology of the Nuclear Region in the Hard Continuum and Fe Kα Line

We report the results of high-resolution subpixel imaging of the hard continuum and Fe K{\alpha} line of the Compton Thick (CT) Active Galactic Nucleus (AGN) ESO 428-G014, observed with Chandra ACIS. While the 3-4 keV emission is dominated by an extended component, a single nuclear point source is prominent in the 4-6 keV range. Instead, two peaks of similar intensity, separated by ~36 pc in projection on the plane of the sky are detected in the Fe K{\alpha} emission. The SE knot could be marginally associated with the heavily obscured hard continuum source. We discuss four possible interpretations of the nuclear morphology. (1) Given the bolometric luminosity and likely black hole (BH) mass of ESO 428-G014, we may be imaging two clumps of the CT obscuring torus in the Fe K{\alpha} line. (2) The Fe K{\alpha} knots may be connected with the fluorescent emission from the dusty bicone, or (3) with the light echo of a nuclear outburst. (4) We also explore the less likely possibility that we may be detecting the rare signature of merging nuclei. Considering the large-scale kpc-size extent of the hard continuum and Fe K{\alpha} emission (Papers I and II), we conclude that the AGN in ESO 428-G014 has been active for at least 104 yrs. Comparison with the models of Czerny et al (2009) suggests high accretion rates during this activity.

arXiv:1811.06440v1 [pdf, other]
Comprehensive analysis of HD 105, a young Solar System analog
Comments: 12 pages, 6 figures, 4 tables, accepted for publication in ApJ

HD~105 is a nearby, pre-main sequence G0 star hosting a moderately bright debris disc ($L_{\rm dust}/L_{\star} \sim 2.6\times10^{-4}$). HD~105 and its surroundings might therefore be considered an analogue of the young Solar System. We refine the stellar parameters based on an improved Gaia parallax distance, identify it as a pre-main sequence star {with an age of 50~$\pm$~16~Myr}. The circumstellar disc was marginally resolved by \textit{Herschel}/PACS imaging at far-infrared wavelengths. Here we present an archival ALMA observation at 1.3~mm, revealing the extent and orientation of the disc. We also present \textit{HST}/NICMOS and VLT/SPHERE near-infrared images, where we recover the disc in scattered light at the $\geq$~5-$\sigma$ level. This was achieved by employing a novel annular averaging technique, and is the first time this has been achieved for a disc in scattered light. Simultaneous modelling of the available photometry, disc architecture, and detection in scattered light allow better determination of the disc's architecture, and dust grain minimum size, composition, and albedo. We measure the dust albedo to lie between 0.19 and 0.06, the lower value being consistent with Edgeworth-Kuiper belt objects.

arXiv:1811.06454v1 [pdf, other]
Solar Wind Charge Exchange: An Astrophysical Nuisance
Comments: Invited review for The Astronomy and Astrophysics Review, 71 pages, 27 figures

Solar Wind Charge-Exchange (SWCX) emission is present in every X-ray observation of an astrophysical object. The emission is problematic when one cannot remove the foreground by the simultaneous measurement of a nearby field. SWCX emission is a serious impediment to the study of the diffuse hot ISM, including the Galactic halo, as its contribution to diagnostic emission lines is temporally variable. Modeling the SWCX emission, in order to remove it from our observations, has proven to be more difficult than originally anticipated. This work reviews our current understanding of SWCX emission, with special attention to all of the components required for future modeling tools. Since, in the absence of such a tool, observing programs can still be constructed to minimize the effect of SWCX, mitigation strategies are discussed. Although some aspects of SWCX will be very difficult to characterize, progress continues on many fronts.

arXiv:1811.06456v1 [pdf, other]
Probing the inflationary evolution using analytical solutions

We transform the Klein-Gordon equation as a first order differential equation for $\epsilon(\phi)$ (or $\epsilon(N)$) which becomes separable for an exponential potential and then derive the general analytical solution in terms of the inverse function $\phi(\epsilon)$ ($N(\epsilon)$). Next, we demonstrate how this solution can provide information about initial conditions independence and attracting behaviour of any single field inflationary model in an expanding FLRW background. We generalize the previous method for multiple fields and present a similar solution for a two-fields product-exponential potential. Throughout the paper we emphasize the importance of scaling solutions during inflation.

arXiv:1811.06464v1 [pdf, other]
Impact of using the ultra-high-energy cosmic ray arrival energies to constrain source associations

We present a Bayesian hierarchical model which enables a joint fit of the ultra-high-energy cosmic ray (UHECR) energy spectrum and arrival directions within the context of a physical model for the UHECR phenomenology. In this way, possible associations with astrophysical source populations can be assessed in a physically and statistically principled manner. The importance of including the UHECR energy data and detection effects is demonstrated through simulation studies, showing that the effective GZK horizon is significantly extended for typical reconstruction uncertainties. We also verify the ability of the model to fit and recover physical parameters from CRPropa 3 simulations. Finally, the model is used to assess the fraction of the the publicly available dataset of 231 UHECRs detected by the Pierre Auger Observatory (PAO) which are associated with the Fermi-LAT 2FHL catalogue, a set of starburst galaxies and Swift-BAT hard X-ray sources. We find association fractions of 9.5 (+2.4,-5.9), 22.7 (+6.6, -12.4) and 22.8 (+6.6, -8.0) per cent for the 2FHL, starburst galaxies and Swift-BAT catalogues respectively.

arXiv:1811.06473v1 [pdf, other]
Finding Black Holes with Black Boxes -- Using Machine Learning to Identify Globular Clusters with Black Hole Subsystems
Comments: 20 pages, 9 figures, 7 tables. Submitted to MNRAS. Source code available at https://github.com/ammaraskar/black-holes-black-boxes

Machine learning is a powerful technique, becoming increasingly popular in astrophysics. In this paper, we apply machine learning to more than a thousand globular cluster (GC) models simulated as part of the 'MOCCA-Survey Database I' project in order to correlate present-day observable properties with the presence of a subsystem of stellar mass black holes (BHs). The machine learning model is then applied to available observed parameters for Galactic GCs to identify which of them that are most likely to be hosting a sizeable number of BHs and reveal insights into what properties lead to the formation of BH subsystems. With our machine learning model, we were able to shortlist 21 Galactic GCs that are most likely to contain a BH subsystem. We show that the clusters shortlisted by the machine learning classifier include those in which BH candidates have been observed (M22, M10 and NGC 3201) and that our results line up well with independent simulations and previous studies that manually compared simulated GC models with observed properties of Galactic GCs. These results can be useful for observers searching for elusive stellar mass BH candidates in GCs and further our understanding of the role BHs play in GC evolution. In addition, we have released an online tool that allows one to get predictions from our model after they input observable properties.

arXiv:1811.06476v1 [pdf, other]
Re-analysing the dynamical stability of the HD 47366 planetary system
Comments: 12 pages, 12 figures, 5 tables, accepted for publication in AJ

Multi-planet systems around evolved stars are of interest to trace the evolution of planetary systems into the post-main sequence phase. HD 47366, an evolved intermediate mass star, hosts two giant planets on moderately eccentric orbits. Previous analysis of the planetary system has revealed that it is dynamically unstable on timescales much shorter than the stellar age unless the planets are trapped in mutual 2:1 mean motion resonance, inconsistent with the orbital solution presented in \cite{2016Sato} (hereafter: S16), or are moving on mutually retrograde orbits. Here we examine the orbital stability of the system presented in S16 using the $n$-body code {\sc Mercury} over a broad range of $a$--$e$ parameter space consistent with the observed radial velocities, assuming they are on co-planar orbits. Our analysis confirms that the system as proposed in S16 is not dynamically stable. We therefore undertake a thorough re-analysis of the available observational data for the HD 47366 system, through the Levenberg-Marquardt technique and confirmed by MCMC Bayesian methodology. Our re-analysis reveals an alternative, lower eccentricity fit that is vastly preferred over the highly eccentric orbital solution obtained from the nominal best-fit presented in S16. The new, improved dynamical simulation solution reveals the reduced eccentricity of the planetary orbits, shifting the HD 47366 system into the edge of a broad stability region, increasing our confidence that the planets are all that they seem to be. Our rigorous examination of the dynamical stability of HD 47366 stands as a cautionary tale in finding the global best-fit model.

arXiv:1811.06486v1 [pdf, other]
Searching for the most powerful thermonuclear X-ray bursts with the Neil Gehrels Swift Observatory
Comments: Accepted for publication in Astronomy & Astrophysics, 29 pages, 12 figures

We searched for thermonuclear X-ray bursts from Galactic neutron stars in all event mode data of the Neil Gehrels Swift Observatory collected until March 31, 2018. In particular, we are interested in the intermediate-duration bursts (shell flashes fueled by thick helium piles) with the ill-understood phenomenon of strong flux fluctuations. Nine such bursts have been discussed in the literature to date. Swift is particularly suitable for finding additional examples. We find and list a total of 134 X-ray bursts; 44 are detected with BAT only, 41 with XRT only, and 49 with both. Twenty-eight bursts involve automatic slews. We find 12 intermediate-duration bursts, all detected in observations involving automatic slews. Five show remarkably long Eddington-limited phases in excess of 200 s. Five show fluctuations during the decay phase; four of which are first discussed in the present study. We discuss the general properties of the fluctuations, considering all 12 cases. In general two types of fluctuations are observed: fast ones, with a typical timescale of 1 s and up and downward fluctuations of up to 70%, and slow ones, with a typical timescale of 1 min and only downward fluctuations of up to 90%. The latter look like partial eclipses because the burst decay remains visible in the residual emission. We revisit the interpretation of this phenomenon in the context of the new data set and find that it has not changed fundamentally despite the expanded data set. It is thought to be due to a disturbance of the accretion disk by outflowing matter and photons, causing obscuration and reflection due to Thompson scattering in an orbiting highly ionized cloud or structure above or below the disk. We discuss in detail the most pronounced burster SAX J1712.6-3739. One of the bursts from this source is unusual in that it lasts longer than 5600 s, but does not appear to be a superburst.

arXiv:1811.06487v1 [pdf, other]
On the giant supercluster binary-like system formed by the Corona Borealis and Abell 2142

The recent hypothesis of a giant supercluster binary-like structure formed by the Corona Borealis and its close companion Abell 2142 (supercluster) belongs to a little known area of investigation as the dynamics of gravitationally interacting galaxy supercluster pairs. From the observational point of view this structure approximates the configuration of a binary-like system in linear orbit interconnected by a huge filamentary structure which, if confirmed, it would be the first case to date observed at z > 0.07. Given the importance to disentangle this issue, a follow-up analysis has been performed on the region constrained by the common envelop of the two superclusters in order to search for new hints to confirm their mutual gravitational interaction. Observational signatures of that interaction have been found mapping the inner peculiar motions where the observed negative peculiar velocities measured within the A2142 (supercluster) region suggest a general matter flow toward the Corona Borealis supercluster. Besides, analyzing the effects on both superclusters due to the mutual impact of the external tidal forces, turns out that their inner dynamics remain unperturbed up to the turnaround radii. Outside, where the binding forces are overlapped by the tidal ones, the outskirts of both superclusters should be unstable and subject to fragmentation. Such a scenario indicates that both superclusters interact with comparable and reciprocal tidal perturbations leaving the whole system in a substantial dynamical equilibrium. The origin of such a dynamical dichotomy would be explained either by a much more massive Corona Borealis supercluster than that estimated in the present work or by a selection effect biasing the small sample of peculiar velocities due to the remoteness of the system worsened by the large uncertainty on their measurements.

arXiv:1811.06499v1 [pdf, other]
Cosmological constraints from galaxy-lensing cross correlations using BOSS galaxies with SDSS and CMB lensing

We present cosmological parameter constraints based on a joint modeling of galaxy-lensing cross correlations and galaxy clustering measurements in the SDSS, marginalizing over small-scale modeling uncertainties using mock galaxy catalogs, without explicit modeling of galaxy bias. We show that our modeling method is robust to the impact of different choices for how galaxies occupy dark matter halos and to the impact of baryonic physics (at the $\sim2\%$ level in cosmological parameters) and test for the impact of covariance on the likelihood analysis and of the survey window function on the theory computations. Applying our results to the measurements using galaxy samples from BOSS and lensing measurements using shear from SDSS galaxies and CMB lensing from Planck, with conservative scale cuts, we obtain $S_8\equiv\left(\frac{\sigma_8}{0.8228}\right)^{0.8}\left(\frac{\Omega_m}{0.307}\right)^{0.6}=0.85\pm0.05$ (stat.) using LOWZ $\times$ SDSS galaxy lensing, and $S_8=0.91\pm0.1$ (stat.) using combination of LOWZ and CMASS $\times$ Planck CMB lensing. We estimate the systematic uncertainty in the galaxy-galaxy lensing measurements to be $\sim6\%$ (dominated by photometric redshift uncertainties) and in the galaxy-CMB lensing measurements to be $\sim3\%$, from small scale modeling uncertainties including baryonic physics.

arXiv:1811.06505v1 [pdf, other]
The diversity of supernovae and impostors shortly after explosion
Comments: submitted to A&A. 14 pages, 7 figures

Observational surveys are now able to detect an increasing number of transients, such as core-collapse supernovae (SN) and powerful non-terminal outbursts (SN impostors). Dedicated spectroscopic facilities can follow up these events shortly after detection. Here we investigate the properties of these explosions at early times. We use the radiative transfer code CMFGEN to build an extensive library of spectra simulating the interaction of supernovae and their progenitor's winds/circumstellar medium (CSM). We consider a range of progenitor mass-loss rates ($Mdot = 5 \times 10^{-4}$ to $10^{-2} Msun/yr$), abundances (solar, CNO-processed, and He-rich), and SN luminosities ($L = 1.9 \times 10^8$ to $2.5 \times 10^{10} Lsun$). The models simulate events ~1 day after explosion, and we assume a fixed location of the shock front as $R_{in}=8.6 \times 10^{13}$ cm. We show that the large range of massive star properties at the pre-SN stage causes a diversity of early-time interacting SN and impostors. We identify three main classes of early-time spectra consisting of relatively high-ionisation (e.g. Ovi}), medium-ionisation (e.g. Ciii), and low-ionisation lines (e.g. Feii/iii). They are regulated by $L$ and the CSM density. Given a progenitor wind velocity Vinf, our models also place a lower limit of $Mdot \gtrsim 5 \times 10^{-4}\, (Vinf/150 km/s)\, Msun/yr$ for detection of CSM interaction signatures in observed spectra. Early-time SN spectra should provide clear constraints on progenitors by measuring H, He, and CNO abundances if the progenitors come from single stars. The connections are less clear considering the effects of binary evolution. Yet, our models provide a clear path for linking the final stages of massive stars to their post-explosion spectra at early times, and guiding future observational follow-up of transients with facilities such as the Zwicky Transient Facility.

arXiv:1811.06506v1 [pdf, other]
Two-Fluid Dusty Gas in Smoothed Particle Hydrodynamics: Fast and Implicit Algorithm for Stiff Linear Drag

Simulation of the dynamics of dust-gas circumstellar discs is crucial in understanding the mechanisms of planet formation. The dynamics of small grains in the disc is stiffly coupled to the gas, while the dynamics of grown solids is decoupled. Moreover, in some parts of the disc the concentration of the dust is low (dust to gas mass ratio is about 0.01), while in other parts it can be much higher. These factors place high requirements on the numerical methods for disc simulations. In particular, when gas and dust are simulated with two different fluids, explicit methods require very small timestep (must be less than dust stopping time $t_{\rm stop}$ during which the velocity of a solid particle is equalized with respect to the gas velocity) to obtain solution, while some implicit methods requires high temporal resolution to obtain acceptable accuracy. Moreover, recent studies underlined that for Smoothed particle hydrodynamics (SPH) when the gas and the dust are simulated with different sets of particles only high spatial resolution $h<c_{\rm s} t_{\rm stop}$ guaranties suppression of numerical overdissipation due to gas and dust interaction. To address these problems, we developed a fast algorithm based on the ideas of (1) implicit integration of linear (Epstein) drag and (2) exact conservation of local linear momentum. We derived formulas for monodisperse dust-gas in two-fluid SPH and tested the new method on problems with known analytical solutions. We found that our method is a promising alternative for the previously developed two-fluid SPH scheme in case of stiff linear drag thanks to the fact that spatial resolution condition $h<c_{\rm s} t_{\rm stop}$ is not required anymore for accurate results.

arXiv:1811.06511v1 [pdf, other]
The Splashback Radius of Planck-SZ clusters
Comments: 17 pages, 16 figures, submitted and defended as a Masters thesis by Dominik Zuercher at the DPHYS in ETH Zurich in June 2018

We present evidence for the existence of the splashback radius in galaxy clusters selected using the Sunyaev-Zel'dovich effect. We show that the deprojected cross-correlation of galaxy clusters found in the Planck survey with galaxies detected photometrically in the Pan-STARRS survey, shows a sharp steepening feature (a logarithmic slope steeper than $-3$), which we associate with the splashback radius. We infer the three-dimensional splashback radius for the SZ cluster sample to be $r_{\rm sp}=1.85_{-0.30}^{+0.26}$ $h^{-1}$Mpc, where the cluster sample has an average halo mass $M_{500c}=3.0\times10^{14}h^{-1}M_\odot$ at an average redshift of $z=0.18$. The inferred value of the splashback radius appears consistent with the expected location for dark matter halos in the standard cold dark matter paradigm. However, given the limited precision of our measurements, we cannot conclusively rule out the smaller splashback radius measured so far in the literature for optically selected galaxy clusters. We show that the splashback radius does not depend upon the galaxy magnitude for galaxies fainter than $M_i-5\log h=-19.44$, and is present at a consistent location in galaxy populations divided by color. The presence of the splashback radius in the star-forming galaxy population could potentially be used to put lower limits on the quenching timescales for galaxies. We can marginally rule out the contamination of the star-forming galaxy sample by quenched galaxies, but the results would need further verification with deeper datasets.

arXiv:1811.06522v1 [pdf, other]
Development and application of fast methods for computing momentum transfer between gas and dust in supercomputer simulation of planet formation

Circumstellar discs, from which planetary systems are formed, consist of gas, dust and solids. Simulations of self-consistent dynamics of gas, dust and solids in circumstellar discs is a challenging problem. In the paper we present fast algorithms for computing the drag force (momentum transfer) between solid phase and gas. These algorithms (a) are universal and applicable to dust and solids with any sizes smaller than the mean free path of gas molecules, (b) can be used to calculate the momentum transfer between dust and gas instead of one-way effect, as it is done in many models, (c) can perform simulations, without a loss in accuracy, with the time step determined by gas-dynamic parameters rather than by drag force, and (d) are compatible with the widely used parallel algorithms for solving 3D equations of gas dynamics, hydrodynamic equations for dust, and the collisionless Boltzmann equation for large bodies. Preliminary results of supercomputer simulation of the gas-dust disc dynamics within the developed approach are reported.

arXiv:1811.06527v1 [pdf, other]
The polarization of the planet-hosting WASP-18 system
Comments: 23 pages, 10 Figures, 6 Tables, Accepted to AJ

We report observations of the linear polarization of the WASP-18 system, which harbors a very massive ( approx 10 M_J) planet orbiting very close to its star with an orbital period of 0.94 days. We find the WASP-18 system is polarized at about 200 parts-per-million (ppm), likely from the interstellar medium predominantly, with no strong evidence for phase dependent modulation from reflected light from the planet. We set an upper limit of 40 ppm (99% confidence level) on the amplitude of a reflected polarized light planetary signal. We compare the results with models for a number of processes that may produce polarized light in a planetary system to determine if we can rule out any phenomena with this limit. Models of reflected light from thick clouds can approach or exceed this limit, but such clouds are unlikely at the high temperature of the WASP-18b atmosphere. Additionally, we model the expected polarization resulting from the transit of the planet across the star and find this has an amplitude of about 1.6 ppm, which is well below our detection limits. We also model the polarization due to the tidal distortion of the star by the massive planet and find this is also too small to be measured currently.

arXiv:1811.06530v1 [pdf, other]
The trajectories of galaxies in groups: mass loss and preprocessing
Comments: Accepted for publication in MNRAS, 16 pages, 15 figures

We present a study of environmental effects and preprocessing in a large galaxy group using a high-resolution, zoom-in simulation run with the GASOLINE2 hydrodynamics code. We categorize galaxies that were always in distinct haloes as unaccreted, galaxies that were distinct before accretion onto the main group as single, and galaxies that were in external sub-groups before accretion onto the main group as grouped. The unaccreted galaxy population experiences steady growth in dark matter, gas and stellar mass. Both single- and group-accreted galaxies begin to lose dark matter and gas after first accretion onto any host but continue to grow in stellar mass. Individual trajectories show that galaxies cease mass growth within roughly three virial radii of the main group. Single galaxies continue to form stars until the group virial radius is crossed, when they begin to lose both dark matter and gas. Grouped galaxies peak in mass when joining their external sub-group, indicating that they experience preprocessing. Most accreted galaxies retain their accumulated stellar mass. The total mass loss is dominated by tidal stripping, with evidence for additional gas stripping via ram pressure. Most accreted galaxies are quenched $\sim$(0.5-2.5) Gyr after accretion onto any group. These differing histories place unaccreted, single and grouped galaxies in distinct regions of the stellar mass-to-halo mass (SMHM) relation. This suggests that preprocessed galaxies are a key source of scatter in the SMHM relation for mixed galaxy populations.

arXiv:1811.06532v1 [pdf, other]
Primordial Black Holes With Multi-Modal Mass Spectra

A mechanism for generating primordial black hole mass spectra with many spikes is proposed and investigated. This mechanism relies on the choice of non-Bunch-Davies vacua, these leading to oscillatory features in the inflationary power spectrum. This in turn generates oscillations in the primordial black hole mass function with exponentially enhanced spikes. This "multi-modal" effect is demonstrated for most of the well-studied models of primordial black hole formation.

arXiv:1811.06533v1 [pdf, other]
Learning to Predict the Cosmological Structure Formation
Comments: 7 pages, 5 figures, 1 table

Matter evolved under influence of gravity from minuscule density fluctuations. Non-perturbative structure formed hierarchically over all scales, and developed non-Gaussian features in the Universe, known as the Cosmic Web. To fully understand the structure formation of the Universe is one of the holy grails of modern astrophysics. Astrophysicists survey large volumes of the Universe and employ a large ensemble of computer simulations to compare with the observed data in order to extract the full information of our own Universe. However, to evolve trillions of galaxies over billions of years even with the simplest physics is a daunting task. We build a deep neural network, the Deep Density Displacement Model (hereafter D$^3$M), to predict the non-linear structure formation of the Universe from simple linear perturbation theory. Our extensive analysis, demonstrates that D$^3$M outperforms the second order perturbation theory (hereafter 2LPT), the commonly used fast approximate simulation method, in point-wise comparison, 2-point correlation, and 3-point correlation. We also show that D$^3$M is able to accurately extrapolate far beyond its training data, and predict structure formation for significantly different cosmological parameters. Our study proves, for the first time, that deep learning is a practical and accurate alternative to approximate simulations of the gravitational structure formation of the Universe.

arXiv:1811.06536v1 [pdf, other]
Seismicity on Tidally Active Solid-Surface Worlds
Comments: 31 pages, 5 pages, submitted to Icarus

Tidal interactions between planets or stars and the bodies that orbit them dissipate energy in their interiors. The energy dissipated drives internal heating and a fraction of that energy will be released as seismic energy. Here we formalize a model to describe the tidally-driven seismic activity on planetary bodies based on tidal dissipation.