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[1]  arXiv:1610.06926 [pdf, ps, other]
Title: Explaining the variability of WD 1145+017 with simulations of asteroid tidal disruption
Comments: Accepted in MNRAS. Movies here!: this http URL
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)

Post-main-sequence planetary science has been galvanised by the striking variability, depth and shape of the photometric transit curves due to objects orbiting white dwarf WD 1145+017, a star which also hosts a dusty debris disc and circumstellar gas, and displays strong metal atmospheric pollution. However, the physical properties of the likely asteroid which is discharging disintegrating fragments remain largely unconstrained from the observations. This process has not yet been modelled numerically. Here, we use the N-body code PKDGRAV to compute dissipation properties for asteroids of different spins, densities, masses, and eccentricities. We simulate both homogeneous and differentiated asteroids, for up to two years, and find that the disruption timescale is strongly dependent on density and eccentricity, but weakly dependent on mass and spin. We find that primarily rocky differentiated bodies with moderate (~3-4 g/cm^3) bulk densities on near-circular (e <~ 0.1) orbits can remain intact while occasionally shedding mass from their mantles. These results suggest that the asteroid orbiting WD 1145+017 is differentiated, resides just outside of the Roche radius for bulk density but just inside the Roche radius for mantle density, and is more akin physically to an asteroid like Vesta instead of one like Itokawa.

[2]  arXiv:1610.06927 [pdf, ps, other]
Title: The overlooked role of stellar variability in the extended main sequence of LMC intermediate-age clusters
Authors: Ricardo Salinas (Gemini), Michael A. Pajkos (Butler), Jay Strader (Michigan St.), A. Katherina Vivas (CTIO), Rodrigo Contreras Ramos (PUC/MAS)
Comments: Resubmitted to ApJ Letters after referee's comments
Subjects: Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)

Intermediate-age star clusters in the Large Magellanic Cloud show extended main sequence turn offs (MSTOs), which are not consistent with a canonical single stellar population. These broad turn offs have been interpreted as evidence for extended star formation and/or stellar rotation. Since most of these studies use single frames per filter to do the photometry, the presence of variable stars near the MSTO in these clusters has remained unnoticed and their impact totally ignored. We model the influence of Delta Scuti using synthetic CMDs, adding variable stars following different levels of incidence and amplitude distributions. We show that Delta Scuti observed at a single phase will produce a broadening of the MSTO without affecting other areas of a CMD like the upper MS or the red clump; furthermore, the amount of spread introduced correlates with cluster age as observed. This broadening is constrained to ages ~ 1-3 Gyr when the MSTO area crosses the instability strip, which is also consistent with observations. Variable stars cannot explain bifurcated MSTOs or the extended MSTOs seen in some young clusters, but they can make an important contribution to the extended MSTOs in intermediate-age clusters.

[3]  arXiv:1610.06928 [pdf, ps, other]
Title: The second closest gamma-ray burst: sub-luminous GRB 111005A with no supernova in a super-solar metallicity environment
Comments: Submitted to A&A. 16 pages, 15 figures, 5 tables. Comments welcome!
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Astrophysics of Galaxies (astro-ph.GA)

We report the detection of the radio afterglow of a long gamma-ray burst (GRB) 111005A at 5-345 GHz, including the very long baseline interferometry observations with the positional error of 0.2 mas. The afterglow position is coincident with the disk of a galaxy ESO 580-49 at z= 0.01326 (~1" from its center), which makes GRB 111005A the second closest GRB known to date, after GRB 980425. The radio afterglow of GRB 111005A was an order of magnitude less luminous than those of local low-luminosity GRBs, and obviously than those of cosmological GRBs. The radio flux was approximately constant and then experienced an unusually rapid decay a month after the GRB explosion. Similarly to only two other GRBs, we did not find the associated supernovae (SN), despite deep near- and mid-infrared observations 1-9 days after the GRB explosion, reaching ~20 times fainter than other SNe associated with GRBs. Moreover, we measured twice solar metallicity for the GRB location. The low gamma-ray and radio luminosities, rapid decay, lack of a SN, and super-solar metallicity suggest that GRB 111005A represents a different rare class of GRBs than typical core-collapse events. We modelled the spectral energy distribution of the GRB 111005A host finding that it is a dwarf, moderately star-forming galaxy, similar to the host of GRB 980425. The existence of two local GRBs in such galaxies is still consistent with the hypothesis that the GRB rate is proportional to the cosmic star formation rate (SFR) density, but suggests that the GRB rate is biased towards low SFRs. Using the far-infrared detection of ESO 580-49, we conclude that the hosts of both GRBs 111005A and 980425 exhibit lower dust content than what would be expected from their stellar masses and optical colours.

[4]  arXiv:1610.06932 [pdf, ps, other]
Title: The RESOLVE Survey Atomic Gas Census and Environmental Influences on Galaxy Gas Reservoirs
Comments: 24 pages, 13 figures, accepted for publication in ApJ, data tables available at this http URL
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present the HI mass inventory for the RESOLVE survey, a volume-limited, multi-wavelength census of >1500 z=0 galaxies spanning diverse environments and complete in baryonic mass down to dwarfs of 10^9 Msun. This first 21cm data release provides robust detections or strong upper limits (1.4M_HI < 5 to 10% of stellar mass M_stars) for 94% of RESOLVE. We examine global atomic gas-to-stellar mass ratios (G/S) in relation to galaxy environment using several metrics: group dark matter halo mass M_h , central/satellite designation, relative mass density of the cosmic web, and distance to nearest massive group. We find that at fixed M_stars, satellites have decreasing G/S with increasing M_h starting clearly at M_h = 10^12 Msun, suggesting the presence of starvation and/or stripping mechanisms associated with halo gas heating in intermediate-mass groups. The analogous relationship for centrals is uncertain because halo abundance matching builds in relationships between central G/S, stellar mass, and halo mass, which depend on the integrated group property used as a proxy for halo mass (stellar or baryonic mass). On larger scales G/S trends are less sensitive to the abundance matching method. At fixed M_h < 10^12 Msun, the fraction of gas-poor centrals increases with large-scale structure density. In overdense regions, we identify a rare population of gas-poor centrals in low-mass (M_h < 10^11.4 Msun) halos primarily located within 1.5 times the virial radius of more massive (M_h > 10^12 Msun) halos, suggesting that gas stripping and/or starvation may be induced by interactions with larger halos or the surrounding cosmic web. We find that the detailed relationship between G/S and environment varies when we examine different subvolumes of RESOLVE independently, which we suggest may be a signature of assembly bias.

[5]  arXiv:1610.06933 [pdf, other]
Title: General Constraints on Dark Matter Decay from the Cosmic Microwave Background
Comments: 15 pages, 12 figures, 2 tables. Comments welcome
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph)

Precise measurements of the temperature and polarization anisotropies of the cosmic microwave background can be used to constrain the annihilation and decay of dark matter. In this work, we demonstrate via principal component analysis that the imprint of dark matter decay on the cosmic microwave background can be approximately parameterized by a single number for any given dark matter model. We develop a simple prescription for computing this model-dependent detectability factor, and demonstrate how this approach can be used to set model-independent bounds on a large class of decaying dark matter scenarios. We repeat our analysis for decay lifetimes shorter than the age of the universe, allowing us to set constraints on metastable species other than the dark matter decaying at early times, and decays that only liberate a tiny fraction of the dark matter mass energy. We set precise bounds and validate our principal component analysis using a Markov Chain Monte Carlo approach and Planck 2015 data.

[6]  arXiv:1610.06939 [pdf, other]
Title: New fully empirical calibrations of strong-line metallicity indicators in star forming galaxies
Comments: 18 pages, 11 figures, MNRAS accepted
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We derive new empirical calibrations for strong-line diagnostics of gas phase metallicity in local star forming galaxies by uniformly applying the Te method over the full metallicity range probed by the Sloan Digital Sky Survey (SDSS). To measure electron temperatures at high metallicity, where the auroral lines needed are not detected in single galaxies, we stacked spectra of more than 110,000 galaxies from the SDSS in bins of log[O II]/H$\beta$ and log[O III]/H$\beta$. This stacking scheme does not assume any dependence of metallicity on mass or star formation rate, but only that galaxies with the same line ratios have the same oxygen abundance. We provide calibrations which span more than 1 dex in metallicity and are entirely defined on a consistent absolute Te metallicity scale for galaxies. We apply our calibrations to the SDSS sample and find that they provide consistent metallicity estimates to within 0.05 dex.

[7]  arXiv:1610.06951 [pdf, other]
Title: Physical parameters of late M-type members of Chamaleon I and TW Hydrae Association: Dust settling, age dispersion and activity
Comments: 26 pages, 22 figures, 10 tables. Accepted in MNRAS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Although mid-to-late type M dwarfs are the most common stars in our stellar neighborhood, our knowledge of these objects is still limited. Open questions include the evolution of their angular momentum, internal structures, dust settling in their atmospheres, age dispersion within populations. In addition, at young ages, late-type Ms have masses below the hydrogen burning limit and therefore are key objects in the debate on the brown dwarf mechanism of formation. In this work we determine and study in detail the physical parameters of two samples of young, late M-type sources belonging to either the Chamaeleon I Dark Cloud or the TW Hydrae Association and compare them with the results obtained in the literature for other young clusters and also for older, field, dwarfs. We used multi-wavelength photometry to construct and analyze SEDs to determine general properties of the photosphere and disk presence. We also used low resolution optical and near-infrared spectroscopy to study activity, accretion, gravity and effective temperature sensitive indicators. We propose a VO-based spectral index that is both temperature and age sensitive. We derived physical parameters using independent techniques confirming the already common feature/problem of the age/luminosity spread. In particular, we highlight two brown dwarfs showing very similar temperatures but clearly different surface gravity (explained invoking extreme early accretion). We also show how, despite large improvement in the dust treatment in theoretical models, there is still room for further progress in the simultaneous reproduction of the optical and near-infrared features of these cold young objects.

[8]  arXiv:1610.06970 [pdf, ps, other]
Title: Singular diffusionless limits of double-diffusive instabilities in magnetohydrodynamics
Authors: Oleg N. Kirillov
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Fluid Dynamics (physics.flu-dyn); Plasma Physics (physics.plasm-ph)

We study local instabilities of a differentially rotating viscous flow of electrically conducting incompressible fluid subject to an external azimuthal magnetic field. In the presence of the magnetic field the hydrodynamically stable flow can demonstrate the azimuthal magnetorotational instability (AMRI) both in the diffusionless case and in the double--diffusive case with viscous and ohmic dissipation. Performing stability analysis of the amplitude transport equations of the short--wavelength approximation, we find that the threshold of the diffusionless AMRI via the Hamilton-Hopf bifurcation is a singular limit of the thresholds of the viscous and resistive AMRI corresponding to the dissipative Hopf bifurcation and manifests itself as the Whitney umbrella singular point. A smooth transition between the two types of instabilities is possible only if the magnetic Prandtl number is equal to unity, $\rm Pm=1$. At a fixed ${\rm Pm}\ne 1$ the threshold of the double-diffusive AMRI is displaced by an order one distance in the parameter space with respect to the diffusionless case even in the zero dissipation limit. The complete neutral stability surface contains three Whitney umbrella singular points and two mutually orthogonal intervals of self-intersection. At these singularities the double-diffusive system reduces to a marginally stable system which is either Hamiltonian or parity-time (PT) symmetric.

[9]  arXiv:1610.07002 [pdf, ps, other]
Title: Lick Indices and Spectral Energy Distribution Analysis based on an M31 Star Cluster Sample: Comparisons of Methods and Models
Comments: 7 tables, 11 figures, accepted for publication in AJ
Subjects: Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)

Application of fitting techniques to obtain physical parameters---such as ages, metallicities, and $\alpha$-element to iron ratios---of stellar populations is an important approach to understand the nature of both galaxies and globular clusters (GCs). In fact, fitting methods based on different underlying models may yield different results, and with varying precision. In this paper, we have selected 22 confirmed M31 GCs for which we do not have access to previously known spectroscopic metallicities. Most are located at approximately one degree (in projection) from the galactic center. We performed spectroscopic observations with the 6.5 m MMT telescope, equipped with its Red Channel Spectrograph. Lick/IDS absorption-line indices, radial velocities, ages, and metallicities were derived based on the $\rm EZ\_Ages$ stellar population parameter calculator. We also applied full spectral fitting with the ULySS code to constrain the parameters of our sample star clusters. In addition, we performed $\chi^2_{\rm min}$ fitting of the clusters' Lick/IDS indices with different models, including the Bruzual & Charlot models (adopting Chabrier or Salpeter stellar initial mass functions and 1994 or 2000 Padova stellar evolutionary tracks), the GALEV, and the Thomas et al. models. For comparison, we collected their $UVBRIJK$ photometry from the Revised Bologna Catalogue (v.5) to obtain and fit the GCs' spectral energy distributions (SEDs). Finally, we performed fits using a combination of Lick/IDS indices and SEDs. The latter results are more reliable and the associated error bars become significantly smaller than those resulting from either our Lick/IDS indices-only or our SED-only fits.

[10]  arXiv:1610.07003 [pdf, other]
Title: Delay Spectrum with Phase-Tracking Arrays: Extracting the HI power spectrum from the Epoch of Reionization
Comments: 17 pages, 10 figures, accepted for publication in The Astrophysical Journal
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

The Detection of redshifted 21 cm emission from the epoch of reionization (EoR) is a challenging task owing to strong foregrounds that dominate the signal. In this paper, we propose a general method, based on the delay spectrum approach, to extract HI power spectra that is applicable to tracking observations using an imaging radio interferometer (Delay Spectrum with Imaging Arrays (DSIA)). Our method is based on modelling the HI signal taking into account the impact of wide field effects such as the $w$-term which are then used as appropriate weights in cross-correlating the measured visibilities. Our method is applicable to any radio interferometer that tracks a phase center and could be utilized for arrays such as MWA, LOFAR, GMRT, PAPER and HERA. In the literature the delay spectrum approach has been implemented for near-redundant baselines using drift scan observations. In this paper we explore the scheme for non-redundant tracking arrays, and this is the first application of delay spectrum methodology to such data to extract the HI signal. We analyze 3 hours of MWA tracking data on the EoR1 field. We present both 2-dimensional ($k_\parallel,k_\perp$) and 1-dimensional (k) power spectra from the analysis. Our results are in agreement with the findings of other pipelines developed to analyse the MWA EoR data.

[11]  arXiv:1610.07014 [pdf, ps, other]
Title: The Local Bubble in the interstellar medium and the origin of the low energy cosmic rays
Comments: 5 pages, accepted for publication in 'Advances in Space Research'
Subjects: Astrophysics of Galaxies (astro-ph.GA)

An analysis of the energy spectra of cosmic rays and particularly the precise data from the AMS-02 experiment support the view about the important role of the Local Bubble in the nearby interstellar medium. It is suggested that the bulk of cosmic rays below about 200 GV of rigidity (momentum/charge ratio) comes from the modest number of supernova remnants in the Local Bubble which appear to have occurred some $10^6$ years ago and contributed to its formation. At higher rigidities the contribution from a 'Local Source', a single supernova remnant generated some $10^5$ years ago seems to dominate up to, at least 1000 GV.

[12]  arXiv:1610.07015 [pdf, other]
Title: On the IceCube spectral anomaly
Comments: 10 pages, 4 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Recently it was noted that different IceCube datasets are not consistent with the same power law spectrum of the cosmic neutrinos: this is the IceCube spectral anomaly, that suggests that they observe a multicomponent spectrum. In this work, the main possibilities to enhance the description in terms of a single extragalactic neutrino component are examined. The hypothesis of a sizable contribution of Galactic high-energy neutrino events distributed as $E^{-2.7}$ [ApJ 826, 185 (2016)] is critically analyzed and its natural generalization is considered. The stability of the expectations is studied by introducing free parameters, motivated by theoretical considerations and observational facts. The upgraded model here examined has 1)~a Galactic component with different normalization and shape $E^{- 2.4}$; 2)~an extragalactic neutrino spectrum based on new data; 3)~a non-zero prompt component of atmospheric neutrinos. The two key predictions of the model concern the `high-energy starting events' collected from the Southern sky. The Galactic component produces a softer spectrum and a testable angular anisotropy. A second, radically different class of models, where the second component is instead isotropic, plausibly extragalactic and with a relatively soft spectrum, is disfavored instead by existing observations of muon neutrinos from the Northern sky and below few 100 TeV.

[13]  arXiv:1610.07056 [pdf]
Title: UY Puppis A New Anomalous Z Cam Type Dwarf Nova
Comments: 10 pages, 5 figures, accepted for publication in the Journal of the AAVSO
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

The defining characteristic of Z Cam stars are standstills in their light curves. Some Z Cams exhibit atypical behaviour by going into outburst from a standstill. It has previously been suggested that UY Pup had been a Z Cam star, but it was ruled out due to its long-term light curve. However, in December 2015 UY Pup went into outburst and unexpectedly entered into a short standstill instead of returning to quiescence. Furthermore, UY Pup exhibited additional unusual behaviour with two outbursts detected during its standstill. After this standstill UY Pup made a brief excursion to a quiescence state and slowly rose to a longer and well-defined standstill, where it again went into another outburst. Through comparative analysis, researching and observational data of UY Pup it is evident and thus concluded that it is indeed a Z Cam star, in which renders it to be one of only four known anomalous Z Cam stars.

[14]  arXiv:1610.07060 [pdf, other]
Title: On the nature and correction of the spurious S-wise spiral galaxy winding bias in Galaxy Zoo 1
Comments: 17 pages, 2 tables, 6 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA)

The Galaxy Zoo 1 catalog displays a bias towards the S-wise winding direction in spiral galaxies which has yet to be explained. The lack of an explanation confounds our attempts to verify the Cosmological Principle, and has spurred some debate as to whether a bias exists in the real universe. The bias manifests not only in the obvious case of trying to decide if the universe as a whole has a winding bias, but also in the more insidious case of selecting which galaxies to include in a winding direction survey. While the former bias has been accounted for in a previous image-mirroring study, the latter has not. Furthermore, the bias has never been {\em corrected} in the GZ1 catalog, as only a small sample of the GZ1 catalog was re-examined during the mirror study. We show that the existing bias is a human {\em selection} effect rather than a human chirality bias. In effect, the excess S-wise votes are spuriously "stolen" from the elliptical and edge-on-disk categories, not the Z-wise category. Thus, when selecting a set of spiral galaxies by imposing a threshold $T$ so that $\max(P_S,P_Z) > T$ or $P_S+P_Z>T$, we spuriously select more S-wise than Z-wise galaxies. We show that when a provably unbiased machine selects which galaxies are spirals independent of their chirality, the S-wise surplus vanishes, even if humans are still used to determine the chirality. Thus, when viewed across the entire GZ1 sample (and by implication, the Sloan catalog), the winding direction of arms in spiral galaxies as viewed from Earth is consistent with the flip of a fair coin.

[15]  arXiv:1610.07062 [pdf, ps, other]
Title: Recovering lost 21 cm radial modes via cosmic tidal reconstruction
Comments: 5 pages, 3 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

21 cm intensity mapping has emerged as a promising technique to map the large-scale structure of the Universe, at redshifts $z$ from 1 to 10. Unfortunately, many of the key cross correlations with photo-$z$ galaxies and the CMB have been thought to be impossible due to foreground contamination for radial modes with small wavenumbers. These modes are usually subtracted in the foreground subtraction process. We recover the lost 21 cm radial modes via cosmic tidal reconstruction and find more than 60\% cross-correlation signal at $\ell\lesssim100$ and even more on larger scales can be recovered from null. The tidal reconstruction method opens up a new set of possibilities to probe our Universe and is extremely valuable not only for 21 cm surveys but also for CMB and photometric redshift observations.

[16]  arXiv:1610.07071 [pdf, ps, other]
Title: Fabrication and Analysis of Three-Layer All-Silicon Interference Optical Filter with Sub-Wavelength Structure toward High Performance Terahertz Optics
Comments: Accepted for publication in J Infrared Milli Terahz Waves. The final publication will be available at Springer via this http URL
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

We propose an all-silicon multi-layer interference filter composed solely of silicon with sub-wavelength structure (SWS) in order to realize high performance optical filters operating in the THz frequency region with robustness against cryogenic thermal cycling and mechanical damage. We demonstrate fabrication of a three-layer prototype using well-established common micro-electro-mechanical systems (MEMS) technologies as a first step toward developing practical filters. The measured transmittance of the three-layer filter agrees well with the theoretical transmittances calculated by a simple thin-film calculation with effective refractive indices as well as a rigorous coupled-wave analysis simulation. We experimentally show that SWS layers can work as homogeneous thin-film interference layers with effective refractive indices even if there are multiple SWS layers in a filter.

[17]  arXiv:1610.07112 [pdf, other]
Title: Lagrangian Space Nonlinear $E$-mode clustering
Comments: 5 pages, 4 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We study the nonlinear $E$-mode clustering in Lagrangian space by using large scale structure (LSS) $N$-body simulations and use the displacement field information in Lagrangian space to recover the primordial linear density field. We find that, compared to Eulerian nonlinear density fields, the $E$-mode displacement fields in Lagrangian space improves the cross-correlation scale $k$ with initial density field by factor of 6 $\sim$ 7, containing 2 orders of magnitude more primordial information. This illustrates ability of potential density reconstruction algorithms, to improve the baryonic acoustic oscillation (BAO) measurements from current and future large scale structure surveys.

[18]  arXiv:1610.07139 [pdf, other]
Title: A Monte Carlo Study of Flux Ratios of Raman Scattered O~VI Features at 6825 Å and 7082 Å in Symbiotic Stars
Comments: 15 pages, 9 figures, accepted for publication in ApJ
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Symbiotic stars are regarded as wide binary systems consisting of a hot white dwarf and a mass losing giant. They exhibit unique spectral features at 6825 \AA\ and 7082 \AA, which are formed via Raman scattering of \ion{O}{6}$\lambda\lambda$ 1032 and 1038 with atomic hydrogen. We adopt a Monte Carlo technique to generate the same number of \ion{O}{6}$\lambda$1032 and $\lambda$1038 line photons and compute the flux ratio $F(6825)/F(7082)$ of these Raman scattered \ion{O}{6} features formed in neutral regions with a simple geometric shape as a function of \ion{H}{1} column density $N_{HI}$. In cylindrical and spherical neutral regions with the \ion{O}{6} source embedded inside, the flux ratio $F(6825)/F(7082)$ shows an overall decrease from 3 to 1 as $N_{HI}$ increases in the range $10^{22-24}{\rm\ cm^{-2}}$. In the cases of a slab geometry and other geometries with the \ion{O}{6} source outside the \ion{H}{1} region, Rayleigh escape operates to lower the flux ratio considerably. For moderate values of $N_{HI}\sim 10^{23}{\rm\ cm^{-2}}$ the flux ratio behaves in a complicated way to exhibit a broad bump with a peak value of 3.5 in the case of a sphere geometry. We find that the ratio of Raman conversion efficiencies of \ion{O}{6}$\lambda\lambda$1032, 1038 ranges from 0.8 to 3.5. Our high resolution spectra of 'D' type HM~Sge and 'S' type AG~Dra obtained with the {\it Canada-France-Hawaii-Telescope} show that the flux ratio $F(6825)/F(7082)$ of AG~Dra is significantly smaller than that of HM~Sge, implying that 'S' type symbiotics are characterized by higher $N_{HI}$ than 'D' type symbiotics.

[19]  arXiv:1610.07154 [pdf, other]
Title: Geographic and seasonal influences on optical followup of gravitational wave events
Authors: Varun Srivastava (1), Varun Bhalerao (2), Aravind P. Ravi (3 and 4), Archisman Ghosh (4 and 5), Sukanta Bose (2 and 6), ((1) IISER Pune, (2) IUCAA, (3) IISER Kolkata, (4) ICTS Bangalore, (5) Nikhef - National Institute for Subatomic Physics, (6) Department of Physics & Astronomy, Washington State University)
Comments: 14 pages, 10 figures, Submitted to ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Instrumentation and Methods for Astrophysics (astro-ph.IM)

We investigate the effects of observatory locations on the probability of discovering optical/infrared counterparts of gravitational wave sources. We show that for the LIGO--Virgo network, the odds of discovering optical/infrared (OIR) counterparts show some latitude dependence, but weak or no longitudinal dependence. A stronger effect is seen to arise from the timing of LIGO/Virgo observing runs, with northern OIR observatories having better chances of finding the counterparts in northern winters. Assuming identical technical capabilities, the tentative mid-2017 three-detector network observing favors southern OIR observatories for discovery of EM counterparts.

[20]  arXiv:1610.07157 [pdf, ps, other]
Title: A Profile Analysis of Raman-scattered O VI Bands at 6825 Å and 7082 Å in Sanduleak's Star
Comments: 11 pages, 5 figures, accepted for publication in ApJ
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We present a detailed modeling of the two broad bands observed at 6825 \AA\ and 7082 \AA\ in Sanduleak's star, a controversial object in the Large Magellanic Cloud. These bands are known to originate from Raman-scattering of O VI $\lambda\lambda$ 1032 and 1038 photons with atomic hydrogen and are only observed in bona fide symbiotic stars. Our high-resolution spectrum obtained with the Magellan Inamori Kyocera Echelle (MIKE) spectrograph at the Magellan-Clay Telescope reveals, quite surprisingly, that the profiles of the two bands look very different: while the Raman 6825 \AA\ band shows a single broad profile with a redward extended bump, the Raman 7082 \AA\ band exhibits a distinct triple-peak profile. Our model suggests that the O VI emission nebula can be decomposed into a red, blue and central emission regions from an accretion disk, a bipolar outflow and a further compact, optically thick region. We also perform Monte Carlo simulations with the aim of fitting the observed flux ratio $F(6825)/F(7082) \sim 4.5$, which indicate that the neutral region in Sanduleak's star is characterized by the column density $N_{HI} \sim 1 \times 10^{23} {\rm\ cm^{-2}}$.

[21]  arXiv:1610.07188 [pdf, other]
Title: Be Stars Seen by Space Photometry
Comments: 8 pages, 4 figures, invited talk to 2nd BRITE-Constellation Science Conference held in Innsbruck, to be published in the Proceedings of the Polish Astronomical Society, eds: G. Stachowski, E. Poretti, and J. Matthews
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Classical Be stars are introduced as object class and their particular potential for space based photometry is highlighted. A brief summary of the various types of variability observed in Be stars makes clear that an interpretation of every single frequency as a pulsation mode falls short, instead there are as well purely circumstellar variations and those that originate in the immediate stellar to circumstellar interaction region. In particular the latter offer great potential, as they are linked to one of the few remaining great riddles of Be stars, namely how they feed their disks.

[22]  arXiv:1610.07191 [pdf, ps, other]
Title: A New Measurement of the Spectral Lag of Gamma-Ray Bursts and its Implications for Spectral Evolution Behaviors
Comments: 41 pages, 6 figures, submitted to ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We carry out a systematical study of the spectral lag properties of 50 single-pulsed Gamma-Ray Bursts (GRBs) detected by Fermi/GBM. By dividing the light curves into multiple consecutive energy channels we provide a new measurement of the spectral lag which is independent on energy channel selections. We perform a detailed statistical study of our new measurements. We find two similar universal correlations by investigating the correlations between the photon arrival time versus energy and pulse width versus energy, respectively. We also study the spectral evolution behaviors of the GRB pulses and most of them follow neither "hard-to-soft" (HTS) nor "hardness-intensity tracking" (HIT) trends. We find that a GRB pulse with negligible spectral lag would appear to have an HIT behavior and a GRB pulse with significant spectral lag would appear to have an HTS behavior. The HTS might not be a genuinely true behavior.

[23]  arXiv:1610.07202 [pdf, other]
Title: Challenges in Planet Formation
Comments: Invited review in JGR-planets. In press
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Over the past two decades, large strides have been made in the field of planet formation. Yet fundamental questions remain. Here we review our state of understanding of five fundamental bottlenecks in planet formation. These are: 1) the structure and evolution of protoplanetary disks; 2) the growth of the first planetesimals; 3) orbital migration driven by interactions between proto-planets and gaseous disk; 4) the origin of the Solar System's orbital architecture; and 5) the relationship between observed super-Earths and our own terrestrial planets. Given our lack of understanding of these issues, even the most successful formation models remain on shaky ground.

[24]  arXiv:1610.07215 [pdf, ps, other]
Title: Enhancement of small-scale turbulent dynamo by large-scale shear
Authors: Nishant K. Singh (1), Igor Rogachevskii (2,1), Axel Brandenburg (1,3) ((1) Nordita, (2) Ben-Gurion University, (3) University of Colorado)
Comments: 5 pages, 3 figures, submitted to Physical Review Letters
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Fluid Dynamics (physics.flu-dyn); Plasma Physics (physics.plasm-ph)

Using direct numerical simulations we show that large-scale shear in non-helically forced turbulence supports small-scale dynamo action with zero mean magnetic field, i.e., the dynamo growth rate increases with shear and shear enhances or even produces turbulence, which, in turn, further increases the dynamo growth rate. When the production rates of turbulent kinetic energy due to shear and forcing are of the same order, we find scalings for the growth rate $\gamma$ of the small-scale dynamo and the turbulent velocity $u_{\rm rms}$ with shear rate $S$ that are independent of the magnetic Prandtl number: $\gamma \propto |S|$ and $u_{\rm rms} \propto |S|^{2/3}$. Having compensated for shear-induced effects on turbulent velocity, we find that the normalized growth rate of the small-scale dynamo exhibits a universal scaling, $\widetilde{\gamma}\propto |S|^{2/3}$, arising solely from the induction equation for a given velocity field.

[25]  arXiv:1610.07230 [pdf, ps, other]
Title: Merging white dwarfs and SN Ia
Comments: 28 pages, 20 figures, 14 tables, accepted for publication in MNRAS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Using population synthesis, we study a double-degenerate (DD) scenario for SNe Ia, aiming to estimate the maximum possible contribution to the rate of SNe from this scenario and the dependence of the delay-time distribution (DTD) on it. We make an extreme assumption that all mergers of super-Chandrasekhar pairs of CO white dwarfs (WDs) and mergers of CO WDs more massive than 0.47 $M_\odot$ with hybrid or helium WDs more massive than 0.37$M_\odot$ produce SNe Ia. The models are parametrized by the product of the common envelope efficiency and the parameter of binding energy of stellar envelopes $\alpha_{ce}\lambda$, which we vary between 0.25 and 2. The best agreement with observations is obtained for $\alpha_{ce}\lambda$=2. A substantial contribution to the rate of SNe Ia is provided by the pairs with a hybrid WD. The estimated Galactic rate of SNe Ia is $6.5 10^{-3}$ per yr (for the mass of the bulge and thin disk equal to $7.2 10^{10} M_\odot$), which is comparable to the observational estimate $(5.4\pm0.12) 10^{-3}$ per yr. The model DTD for 1 to 8 Gyr range satisfactorily fits DTD for SNe Ia in the field galaxies (Maoz et al. 2012). For this epoch, model DTD is a power low with an index -1.64. At earlier and later epochs our DTD has a deficit of events, as in other studies. Marginal agreement with observational DTD is achieved even if only CO+CO WD with $M_1\geq0.8\,M_\odot$ and $M_2\geq0.6\,M_\odot$ produce SNe Ia. A better agreement of observed and model DTD may be obtained if tidal effects are weaker than assumed and/or metallicity of population is much lower than solar.

[26]  arXiv:1610.07235 [pdf, ps, other]
Title: Spectral Analysis Code: PARAS SPEC
Comments: 20 pages, To be submitted in MNRAS, Comments are welcome
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Instrumentation and Methods for Astrophysics (astro-ph.IM)

The light emitted from the stellar photosphere serves as a unique signature for the nature of stars. The behaviour of these stellar lines depend upon the surface temperature, mass, evolutionary status and chemical composition of the star. With the advent of high-resolution spectrographs coupled with medium to large aperture telescopes around the globe, there is plenty of high-resolution and high signal-to-noise ratio data available to the astronomy community. Apart from radial velocity (RV) studies, such data offer us the unique opportunity to study chemical composition and atmospheric properties of the star. The procedure used to derive these parameters must be automated and well adaptable to data available from any high-resolution spectrograph. We hereby present an IDL code, PARAS SPEC, which was primary designed to handle high-resolution spectroscopy data from PARAS spectrograph coupled with the 1.2~m telescope at Mt. Abu, India. This code is designed to adapt with data from other spectrographs as well. The code PARAS SPEC estimates the stellar atmospheric parameters from the analysis of stellar spectra based on two primary methods, synthetic spectral fitting and equivalent width method. Synthetic spectral fitting method involves fitting of the observed spectrum with different synthetic spectra for a set of stellar parameters. The second method is based on equivalent widths (EWs) that are used to derive abundances for a set of Fe~I and Fe~II lines from the observed spectra. The detailed methodology used to design this code and comparison of the results from literature values are presented in this paper.

[27]  arXiv:1610.07247 [pdf, other]
Title: Radiative transfer modelling of parsec-scale dusty warped discs
Comments: accepted by MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Warped discs have been found on (sub-)parsec scale in some nearby Seyfert nuclei, identified by their maser emission. Using dust radiative transfer simulations we explore their observational signatures in the infrared in order to find out whether they can partly replace the molecular torus. Strong variations of the brightness distributions are found, depending on the orientation of the warp with respect to the line of sight. Whereas images at short wavelengths typically show a disc-like and a point source component, the warp itself only becomes visible at far-infrared wavelengths. A similar variety is visible in the shapes of the spectral energy distributions. Especially for close to edge-on views, the models show silicate feature strengths ranging from deep absorption to strong emission for variations of the lines of sight towards the warp. To test the applicability of our model, we use the case of the Circinus galaxy, where infrared interferometry has revealed a highly elongated emission component matching a warped maser disc in orientation and size. Our model is for the first time able to present a physical explanation for the observed dust morphology as coming from the AGN heated dust. As opposed to available torus models, a warped disc morphology produces a variety of silicate feature shapes for grazing lines of sight, close to an edge-on view. This could be an attractive alternative to a claimed change of the dust composition for the case of the nearby Seyfert 2 galaxy NGC 1068, which harbours a warped maser disc as well.

[28]  arXiv:1610.07249 [pdf, other]
Title: Spitzer Observations Confirm and Rescue the Habitable-Zone Super-Earth K2-18b for Future Characterization
Comments: Accepted for publication in ApJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

The recent detections of two transit events attributed to the super-Earth candidate K2-18b have provided the unprecedented prospect of spectroscopically studying a habitable-zone planet outside the Solar System. Orbiting a nearby M2.5 dwarf and receiving virtually the same stellar insolation as Earth, K2-18b would be a prime candidate for the first detailed atmospheric characterization of a habitable-zone exoplanet using HST and JWST. Here, we report the detection of a third transit of K2-18b near the predicted transit time using the Spitzer Space Telescope. The Spitzer detection demonstrates the periodic nature of the two transit events discovered by K2, confirming that K2-18 is indeed orbited by a super-Earth in a 33-day orbit and ruling out the alternative scenario of two similarly-sized, long-period planets transiting only once within the 75-day K2 observation. We also find, however, that the transit event detected by Spitzer occurred 1.85 hours (7-sigma) before the predicted transit time. Our joint analysis of the Spitzer and K2 photometry reveals that this early occurrence of the transit is not caused by transit timing variations (TTVs), but the result of an inaccurate K2 ephemeris due to a previously undetected data anomaly in the K2 photometry likely caused by a cosmic ray hit. We refit the ephemeris and find that K2-18b would have been lost for future atmospheric characterizations with HST and JWST if we had not secured its ephemeris shortly after the discovery. We caution that immediate follow-up observations as presented here will also be critical in confirming and securing future planets discovered by TESS, in particular if only two transit events are covered by the relatively short 27-day TESS campaigns.

[29]  arXiv:1610.07263 [pdf, other]
Title: Viscous Hydrodynamics Simulations of Circumbinary Accretion Discs: Variability, Quasi-Steady State, and Angular Momentum Transfer
Comments: 24 pages, 20 figures, submitted to MNRAS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)

Circumbinary discs are found in a variety of astrophysical contexts, including around young stellar binaries and supermassive black hole binaries. We carry out a suite of numerical simulations of circumbinary discs, solving the viscous hydrodynamics equations on a polar grid covering an extended disc outside the binary co-orbital region. We use carefully controlled outer boundary conditions and long-term integrations to ensure that the disc reaches a quasi-steady state, in which the time-averaged mass accretion rate onto the binary, $\langle\dot{M}\rangle$, matches the mass supply rate at the outer disc. We focus on binaries with comparable masses, but with a wide range of eccentricities ($e_\mathrm{B}$). For $e_\mathrm{B} \lesssim 0.05$, the mass accretion rate of the binary is modulated with a period of about $5$ times the binary period; otherwise it is modulated at the binary period. The inner part of the circumbinary disc generally becomes coherently eccentric. For low and high $e_\mathrm{B}$, the disc line of apsides precesses around the binary, but for intermediate $e_\mathrm{B}$ ($0.2 - 0.4$), it instead becomes locked with that of the binary. By considering the detailed balance of angular momentum transport through the disc by advection, viscous stress, and gravitational torque, we determine the time-averaged net angular momentum transfer rate to the binary, $\langle\dot{J}\rangle$. The specific angular momentum, $l_0 = \langle\dot{J}\rangle/\langle\dot{M}\rangle$, depends on $e_\mathrm{B}$ in a non-monotonic manner. Contrary to previous claims, we find $l_0$ is positive for most $e_\mathrm{B}$, implying that the binary receives net angular momentum, which may lead to the growth of the binary separation in time. The minimum $l_0$ occurs at intermediate $e_\mathrm{B}$ ($0.2 - 0.4$) and corresponds to the regime where the inner eccentric disc is apsidally aligned with the binary.

[30]  arXiv:1610.07265 [pdf, ps, other]
Title: A Submillimeter Continuum Survey of Local Dust-Obscured Galaxies
Authors: Jong Chul Lee (1), Ho Seong Hwang (2), Gwang-Ho Lee (3) ((1) Korea Astronomy and Space Science Institute, (2) Korea Institute for Advanced Study (3) Seoul National University)
Comments: 10 pages, 2 tables, 4 figures, to appear in ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We conduct a 350 micron dust continuum emission survey of 17 dust-obscured galaxies (DOGs) at z = 0.05-0.08 with the Caltech Submillimeter Observatory (CSO). We detect 14 DOGs with S_350 = 114-650 mJy and S/N > 3. By including two additional DOGs with submillimeter data in the literature, we are able to study dust contents for a sample of 16 local DOGs that consists of 12 bump and 4 power-law types. We determine their physical parameters with a two-component modified blackbody function model. The derived dust temperatures are in the range 57-122 K and 22-35 K for the warm and cold dust components, respectively. The total dust mass and the mass fraction of warm dust component are 3-34$\times10^{7} M_\odot$ and 0.03-2.52%, respectively. We compare these results with those of other submillimeter-detected infrared luminous galaxies. The bump DOGs, the majority of the DOG sample, show similar distributions of dust temperatures and total dust mass to the comparison sample. The power-law DOGs show a hint of smaller dust masses than other samples, but need to be tested with a larger sample. These findings support that the reason why DOGs show heavy dust obscuration is not an overall amount of dust content, but probably the spatial distribution of dust therein.

[31]  arXiv:1610.07268 [pdf, ps, other]
Title: The Effect of Modified Gravity on the Odds of the Bound Violations of the Turn-Around Radii
Authors: Jounghun Lee (Seoul Nat'l Univ.), Baojiu Li (Durham Univ.)
Comments: submitted for publication in ApJ, 8 figures, 1 table
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

The turn-around radii of the galaxy groups shows the imprint of a long battle between their self-gravitational forces and the accelerating space. The standard LambdaCDM cosmology based on the general relativity (GR) predicts the existence of an upper bound on the expectation value of the turn-around radius which is rarely violated by individual galaxy groups. We speculate that a deviation of the gravitational law from GR on the cosmological scale could cause an appreciable shift of the mean turn-around radius to higher values and make the occurrence of the bound violation more probable. Analyzing the data from high-resolution N-body simulations for two specific models with modified gravity (MG) and the standard GR+LambdaCDM cosmology, we determine the turn-around radii of the massive Rockstar groups from the peculiar motions of the galactic halos located in the bound zone where the fifth force generated by MG is expected to be at most partially shielded. We detect a 4 sigma signal of difference in the odds of the bound violations between a fiducial MG and the GR models, proving that the odds of the bound violations increase with the strength of the fifth force produced by the presence of MG. The advantage of using the odds of the bound violations as a complementary diagnostics to probe the nature of gravity is discussed.

[32]  arXiv:1610.07279 [pdf, other]
Title: GOTHIC: Gravitational oct-tree code accelerated by hierarchical time step controlling
Comments: 22 pages, 10 figures, 4 tables, accepted for publication in New Astronomy
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA); Computational Physics (physics.comp-ph)

The tree method is a widely implemented algorithm for collisionless $N$-body simulations in astrophysics well suited for GPU(s). Adopting hierarchical time stepping can accelerate $N$-body simulations; however, it is infrequently implemented and its potential remains untested in GPU implementations. We have developed a Gravitational Oct-Tree code accelerated by HIerarchical time step Controlling named \texttt{GOTHIC}, which adopts both the tree method and the hierarchical time step. The code adopts some adaptive optimizations by monitoring the execution time of each function on-the-fly and minimizes the time-to-solution by balancing the measured time of multiple functions. Results of performance measurements with realistic particle distribution performed on NVIDIA Tesla M2090, K20X, and GeForce GTX TITAN X, which are representative GPUs of the Fermi, Kepler, and Maxwell generation of GPUs, show that the hierarchical time step achieves a speedup by a factor of around 3--5 times compared to the shared time step. The measured elapsed time per step of \texttt{GOTHIC} is 0.30~s or 0.44~s on GTX TITAN X when the particle distribution represents the Andromeda galaxy or the NFW sphere, respectively, with $2^{24} =$~16,777,216 particles. The averaged performance of the code corresponds to 10--30\% of the theoretical single precision peak performance of the GPU.

[33]  arXiv:1610.07286 [pdf, ps, other]
Title: Water delivery from cores to disks: deuteration as a probe of the prestellar inheritance of H2O
Comments: 20 pages, 15 figures, accepted by A&A
Subjects: Astrophysics of Galaxies (astro-ph.GA); Earth and Planetary Astrophysics (astro-ph.EP)

We investigate the delivery of regular and deuterated forms of water from prestellar cores to circumstellar disks. We adopt a semi-analytical axisymmetric two-dimensional collapsing core model with post-processing gas-ice astrochemical simulations, in which a layered ice structure is considered. The physical and chemical evolutions are followed until the end of the main accretion phase. When mass averaged over the whole disk, a forming disk has a similar H2O abundance and HDO/H2O abundance ratio as their precollapse values (within a factor of 2), regardless of time in our models. Consistent with previous studies, our models suggest that interstellar water ice is delivered to forming disks without significant alteration. On the other hand, the local vertically averaged H2O ice abundance and HDO/H2O ice ratio can differ more, by up to a factor of several, depending on time and distance from a central star. Key parameters for the local variations are the fluence of stellar UV photons en route into the disk and the ice layered structure, the latter of which is mostly established in the prestellar stages. We also find that even if interstellar water ice is destroyed by stellar UV and (partly) reformed prior to disk entry, the HDO/H2O ratio in reformed water ice is similar to the original value. This finding indicates that some caution is needed in discussions on the prestellar inheritance of H2O based on comparisons between the observationally derived HDO/H2O ratio in clouds/cores and that in disks/comets. Alternatively, we propose that the ratio of D2O/HDO to HDO/H2O better probes the prestellar inheritance of H2O. It is also found that icy organics are more enriched in deuterium than water ice in forming disks. The differential deuterium fractionation in water and organics is inherited from the prestellar stages.

[34]  arXiv:1610.07323 [pdf, other]
Title: Improving 1D Stellar Models with 3D Atmospheres
Comments: 4 pages, 5 figures; submitted to the conference proceedings: Seismology of the Sun and the Distant Stars 2016
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Stellar evolution codes play a major role in present-day astrophysics, yet they share common issues. In this work we seek to remedy some of those by the use of results from realistic and highly detailed 3D hydrodynamical simulations of stellar atmospheres. We have implemented a new temperature stratification extracted directly from the 3D simulations into the Garching Stellar Evolution Code to replace the simplified atmosphere normally used. Secondly, we have implemented the use of a variable mixing-length parameter, which changes as a function of the stellar surface gravity and temperature -- also derived from the 3D simulations. Furthermore, to make our models consistent, we have calculated new opacity tables to match the atmospheric simulations. Here, we present the modified code and initial results on stellar evolution using it.

[35]  arXiv:1610.07332 [pdf, other]
Title: The advanced stages of stellar evolution: impact of mass loss, rotation, and link with B[e] stars
Comments: 10 pages, 6 figures, to appear in the proceedings of the conference 'The B[e] Phenomenom: Forty Years of Studies'
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

In this paper, we discuss some consequences of rotation and mass loss on the evolved stages of massive star evolution. The physical reasons of the time evolution of the surface velocity are explained, and then we show how the late-time evolution of massive stars are impacted in combination with the effects of mass loss. The most interesting result is that in some cases, a massive star can have a blue-red-blue evolution, opening the possibility that Blue Supergiants are composed by two distinct populations of stars: one just leaving the main sequence and crossing the HRD for the first time, and the other one evolving back to the blue side of the HRD after a Red Supergiant phase. We discuss a few possible observational tests that can allow to distinguish these two populations, and how supergiant B[e] stars fit in this context.

[36]  arXiv:1610.07348 [pdf, other]
Title: Revised Conditions for MRI due to Corotation Theorem
Comments: 5 pages, 2 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We re-analyze the physical conditions for Magneto-rotational Instability (MRI) within a steady axisymmetric stratified disk of plasma, in order to account for the so-called corotation theory (the differential angular velocity depends on the magnetic flux surface). We develop the study of linear stability around an astrophysical background configuration, following the original derivation in \cite{Ba:1995}, but implementing the corotation condition as the orthogonality between the background magnetic field and the angular velocity gradient. We demonstrate that a dependence on the background magnetic field direction is restored in the dispersion relation and, hence, the emergence of MRI is affected too.

[37]  arXiv:1610.07357 [pdf, ps, other]
Title: Infrared Opacities in Dense Atmospheres of Cool White Dwarf Stars
Authors: Piotr M. Kowalski (1), Simon Blouin (2,1), Patrick Dufour (2) ((1) IEK-6 Institute of Energy and Climate Research, Forschungszentrum Juelich, 52425 Juelich, Germany (2) Universite de Montreal, Montreal, Quebec, Canada)
Comments: 6 pages, 5 figures, Proceedings of the EUROWD2016 workshop. To be published in ASPCS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Materials Science (cond-mat.mtrl-sci); Atomic Physics (physics.atom-ph); Computational Physics (physics.comp-ph); Space Physics (

Dense, He-rich atmospheres of cool white dwarfs represent a challenge to the modeling. This is because these atmospheres are constituted of a dense fluid in which strong multi-atomic interactions determine their physics and chemistry. Therefore, the ideal-gas-based description of absorption is no longer adequate, which makes the opacities of these atmospheres difficult to model. This is illustrated with severe problems in fitting the spectra of cool, He-rich stars. Good description of the infrared (IR) opacity is essential for proper assignment of the atmospheric parameters of these stars. Using methods of computational quantum chemistry we simulate the IR absorption of dense He/H media. We found a significant IR absorption from He atoms (He-He-He CIA opacity) and a strong pressure distortion of the H$_2$-He collision-induced absorption (CIA). We discuss the implication of these results for interpretation of the spectra of cool stars.

[38]  arXiv:1610.07360 [pdf, ps, other]
Title: Galactic winds and the origin of large-scale magnetic fields
Comments: 7 pages, 6 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Observations of dwarf galaxies suggest the presence of large-scale magnetic fields. However the size and slow rotation of these galaxies appear insufficient to support a mean-field dynamo action to excite such fields. Here we suggest a new mechanism to explain large-scale magnetic fields in galaxies that are too small to support mean-field dynamo action. The key idea is that we do not identify large-scale and mean magnetic fields. In our scenario the the magnetic structures originate from a small-scale dynamo which produces small-scale magnetic field in the galactic disc and a galactic wind that transports this field into the galactic halo where the large turbulent diffusion increases the scale and order of the field. As a result, the magnetic field becomes large-scale; however its mean value remains vanishing in a strict sense. We verify the idea by numerical modelling of two distinct simplified configurations, a thin disc model using the no-$z$ approximation, and an axisymmetric model using cylindrical $r,z$ coordinates. Each of these allows reduction of the problem to two spatial dimensions. Taken together, the models support the proposition that the general trends will persist in a fully 3D model. We demonstrate that a pronounced large-scale pattern can develop in the galactic halo for a wide choice of the dynamo governing parameters. We believe that our mechanism can be relevant to explaining the presence of the fields observed in the halos of dwarf galaxies. We emphasize that detailed modelling of the proposed scenario needs 3D simulations, and adjustment to the specific dynamo governing parameters of dwarf galaxies.

[39]  arXiv:1610.07385 [pdf, other]
Title: Awakening the BALROG (BAyesian Location Reconstruction Of GRBs): A new paradigm in spectral and location analysis of gamma ray bursts
Comments: 22 pages, 23 figures, submitted to MNRAS
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

The accurate spatial location of gamma-ray bursts (GRBs) is crucial for both producing a detector response matrix (DRM) and follow-up observations by other instruments. The Fermi Gamma-ray Burst Monitor (GBM) has the largest field of view (FOV) for detecting GRBs as it views the entire unocculted sky, but as a non-imaging instrument it relies on the relative count rates observed in each of its 14 detectors to localize transients. Improving its ability to accurately locate GRBs and other transients is vital to the paradigm of multi-messenger astronomy, including the electromagnetic follow-up of gravitational wave signals. Here we present the BAyesian Location Reconstruction Of GRBs ({\tt BALROG}) method for localizing and characterising GBM transients. Our approach eliminates the systematics of previous approaches by simultaneously fitting for the location and spectrum of a source. It also correctly incorporates the uncertainties in the location of a transient into the spectral parameters and produces reliable positional uncertainties for both well-localized sources and those for which the GBM data cannot effectively constrain the position. While computationally expensive, {\tt BALROG} can be implemented to enable quick follow-up of all GBM transient signals. Also, we identify possible response problems that require attention as well as caution when using standard, public GBM DRMs. Finally, we examine the effects of including the variance in location on the spectral parameters of GRB 080916C. We find that spectral parameters change and no extra components are required when these effects are included in contrast to when we use a fixed location. This finding has the potential to alter both the GRB spectral catalogs as well as the reported spectral composition of some well-known GRBs.

[40]  arXiv:1610.07402 [pdf, other]
Title: Consistency of the Planck CMB data and $Λ$CDM cosmology
Comments: 17 pages, 9 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We test the consistency between Planck temperature and polarization power spectra and the concordance model of $\Lambda$ Cold Dark Matter cosmology ($\Lambda$CDM) within the framework of Crossing statistics. We find that Planck TT best fit $\Lambda$CDM power spectrum is completely consistent with EE power spectrum data while EE best fit $\Lambda$CDM power spectrum is not consistent with TT data. However, this does not point to any systematic or model-data discrepancy since in the Planck EE data, uncertainties are much larger compared to the TT data. We also investigate the possibility of any deviation from $\Lambda$CDM model analyzing the Planck 2015 data. Results from both TT and EE data analysis indicate that no deviation is required beyond the flexibility of the concordance $\Lambda$CDM model. Our analysis thus rules out any strong evidence for beyond the concordance model in the Planck spectra data. We also report a mild amplitude difference comparing temperature and polarization data, where temperature data seems to have slightly lower amplitude than expected (consistently at all multiples), as we assume both temperature and polarization data are realizations of the same underlying cosmology.

[41]  arXiv:1610.07427 [pdf, ps, other]
Title: EAS data at the mountain level and a shape of the CR spectrum beyond the break
Authors: S.B.Shaulov
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

In the most works which deal with EAS the CR energy spectrum is deduced by means of the model defined dependence $E_0=a\cdot{N_e}^{\alpha}$. An electron total number $N_e$ is evaluated by integration of the NKG-function f(r). This algorithm breaks down for young EAS with age parameter $s\sim0$. This work shows, that part of the young EAS becomes large in the range $N_e\geq10^7$, it cause to divergency of the $N_e$ integral for them and distorts the shape of EAS (CR) spectrum. A final analysis of the experimental data permits to conclude that EAS spectrum has local maximum at $N_e\sim10^9$, which results in a decrease of the EAS spectrum slope for $N_e\geq10^7$ (inverse break or "knee"). A local maximum can arise because of the additional CR component in the range $E_0\geq10$ PeV.

[42]  arXiv:1610.07449 [pdf, other]
Title: Transverse oscillations in slender Ca II H fibrils observed with Sunrise/SuFI
Comments: Accepted for publication in The Astrophysical Journal Supplement Series
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We present observations of transverse oscillations in slender Ca II H fibrils (SCFs) in the lower solar chromosphere. We use a 1-hour long time series of high (spatial and temporal) resolution, seeing-free observations in a 0.11 nm wide passband covering the line core of Ca II H 396.9 nm from the second flight of the Sunrise balloon-borne solar observatory. The entire field of view, spanning the polarity inversion line of an active region close to the solar disk center, is covered with bright, thin, and very dynamic fine structures. Our analysis reveals the prevalence of transverse waves in SCFs with median amplitudes and periods on the order of 2.4+-0.8 km/s and 83+-29 s, respectively (with standard deviations given as uncertainties). We find that the transverse waves often propagate along (parts of) the SCFs with median phase speeds of 9+-14 km/s. While the propagation is only in one direction along the axis in some of the SCFs, propagating waves in both directions, as well as standing waves are also observed. The transverse oscillations are likely Alfvenic and are thought to be representative of magnetohydrodynamic kink waves. The wave propagation suggests that the rapid, high-frequency transverse waves, often produced in the lower photosphere, can penetrate into the chromosphere, with an estimated energy flux of ~ 15 kW/m^2. Characteristics of these waves differ from those reported for other fibrillar structures, which, however, were observed mainly in the upper solar chromosphere.

[43]  arXiv:1610.07454 [pdf, other]
Title: A large-scale search for evidence of quasi-periodic pulsations in solar flares
Comments: 16 pages, 8 figures, 4 tables. Accepted for publication in The Astrophysical Journal
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

The nature of quasi-periodic pulsations in solar flares is poorly constrained, and critically the general prevalence of such signals in solar flares is unknown. Therefore, we perform a large-scale search for evidence of signals consistent with quasi-periodic pulsations in solar flares, focusing on the 1 - 300s timescale. We analyse 675 M- and X-class flares observed by GOES in 1-8\AA\ soft X-rays between 2011 February 1 and 2015 December 31. Additionally, over the same era we analyse Fermi/GBM 15-25 keV X-ray data for each of these flares that was associated with a Fermi/GBM solar flare trigger, a total of 261 events. Using a model comparison method, we determine whether there is evidence for a substantial enhancement in the Fourier power spectrum that may be consistent with a QPP signature, based on three tested models; a power-law plus a constant, a broken power-law plus constant, and a power-law-plus-constant with an additional QPP signature component. From this, we determine that ~30% of GOES events and ~8% of Fermi/GBM events show strong signatures consistent with classical interpretations of QPP. For the remaining events either two or more tested models cannot be strongly distinguished from each other, or the events are well-described by single power-law or broken power-law Fourier power spectra. For both instruments, a preferred characteristic timescale of ~5-30 s was found in the QPP-like events, with no dependence on flare magnitude in either GOES or GBM data. We also show that individual events in the sample show similar characteristic timescales in both GBM and GOES datasets. We discuss the implications of these results for our understanding of solar flares and possible QPP mechanisms.

[44]  arXiv:1610.07455 [pdf, ps, other]
Title: On the symmetry properties of the PT kernels and recurrence relations
Authors: Paulo Reimberg
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Perturbation Theory to Large Scale Structure Cosmology proposes corrections to the linearly evolved density contrast and velocity in terms of a series development in which all terms are integrals of powers of the linear density contrast multiplied by kernels. We discuss the symmetry properties of these kernels and show that their full symmetrized versions can be decomposed in different classes of subkernels. We will construct classes of subkernels with improved symmetry properties, and provide recurrence relations to generate them.

[45]  arXiv:1610.07470 [pdf, ps, other]
Title: White Dwarf Period Tables - I. Pulsators with hydrogen-dominated atmospheres
Comments: Fun with pulsating white dwarfs. Appeared in IBVS No. 6184. More user-friendly .txt versions of Tables 1-4 are also available both on the IBVS webpage and amongst the source files of this submission. If you find any mistakes (e.g. missing objects or observations), please, let us know. (, Information Bulletin on Variable Stars, 2016, No. 6184
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We aimed at collecting all known white dwarf pulsators with hydrogen-dominated atmospheres and list their main photometric and atmospheric parameters together with their pulsation periods and amplitudes observed at different epochs. For this purpose, we explored the pulsating white dwarf related literature with the systematic use of the SIMBAD and the NASA's Astrophysics Data System (ADS) databases. We summarized our results in four tables listing seven ZZ Ceti stars in detached white dwarf plus main-sequence binaries, seven extremely low-mass DA pulsators, three hot DAVs and 180 ZZ Ceti stars.

[46]  arXiv:1610.07483 [pdf, ps, other]
Title: Cameras a Million Miles Apart: Stereoscopic Imaging Potential with the Hubble and James Webb Space Telescopes
Comments: 9 pages, 3 figures
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Solar and Stellar Astrophysics (astro-ph.SR)

The two most powerful optical/IR telescopes in history -- NASA's Hubble and James Webb Space Telescopes -- will be in space at the same time. We have a unique opportunity to leverage the 1.5 million kilometer separation between the two telescopic nodal points to obtain simultaneously captured stereoscopic images of asteroids, comets, moons and planets in our Solar System. Given the recent resurgence in stereo-3D movies and the recent emergence of VR-enabled mobile devices, these stereoscopic images provide a unique opportunity to engage the public with unprecedented views of various Solar System objects. Here, we present the technical requirements for acquiring stereoscopic images of Solar System objects, given the constraints of the telescopic equipment and the orbits of the target objects, and we present a handful of examples.

[47]  arXiv:1610.07484 [pdf, other]
Title: Solar coronal loops associated with small-scale mixed polarity surface magnetic fields
Comments: Accepted for publication in the Astrophysical Journal Supplement Series; &lt;a href="http://arxiv.orgthis http URL"&gt;online movie&lt;/a&gt;
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

How and where are coronal loops rooted in the solar lower atmosphere? The details of the magnetic environment and its evolution at the footpoints of coronal loops are crucial to understanding the processes of mass and energy supply to the solar corona. To address the above question, we use high resolution line-of-sight magnetic field data from the Imaging Magnetograph eXperiment (IMaX) instrument on the Sunrise balloon-borne observatory and coronal observations from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) of an emerging active region. We find that the coronal loops are often rooted at the locations with minor small-scale but persistent opposite polarity magnetic elements very close to the larger dominant polarity. These opposite polarity small-scale elements continually interact with the dominant polarity underlying the coronal loop through flux cancellation. At these locations we detect small inverse Y-shaped jets in chromospheric Ca II H images obtained from the Sunrise Filter Imager (SuFI) during the flux cancellation. Our results indicate that magnetic flux cancellation and reconnection at the base of coronal loops due to mixed-polarity fields might be a crucial feature for the supply of mass and energy into the corona.

[48]  arXiv:1610.07516 [pdf, ps, other]
Title: Stripped red giants - Helium core white dwarf progenitors and their sdB siblings
Authors: Ulrich Heber
Comments: 6 pages, 3 figures, to appear in 20th European Workshop on White Dwarfs (EuroWD16), eds. Pier-Emmanuel Tremblay, Boris Gaensicke, and Tom Marsh, PASPC 1000
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Some gaps in the mosaic of binary star evolution have recently been filled by the discoveries of helium-core white dwarf progenitors (often called extremely low mass (ELM) white dwarfs) as stripped cores of first-giant branch objects. Two varieties can be distinguished. One class is made up by SB1 binaries, companions being white dwarfs as well, another class, the so-called EL CVn stars, are composite spectrum binaries, with A-Type companions. Pulsating stars are found among both classes. A riddle is posed by the apparently single objects. There is a one-to-one correspondence of the phenomena found for these new classes of star to those observed for sdB stars. In fact, standard evolutionary scenarios explain the origin of sdB stars as red giants that have been stripped close to the tip of first red giant branch. A subgroup of subluminous B stars can also be identified as stripped helium-cores of red giants. They form an extension of the ELM sequence to higher temperatures. Hence low mass white dwarfs of helium cores and sdB stars in binaries are close relatives in terms of stellar evolution.

[49]  arXiv:1610.07518 [pdf, other]
Title: New observational constraints on $f(R)$ gravity from cosmic chronometers
Comments: 11 pages, 4 figures, 6 Tables
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)

We use the recently released cosmic chronometer data and the latest measured value of the local Hubble parameter, combined with the latest joint light curves of Supernovae Type Ia, and Baryon Acoustic Oscillation distance measurements, in order to impose constraints on the viable and most used $f(R)$ gravity models. We consider four $f(R)$ models, namely the Hu-Sawicki, the Starobinsky, the Tsujikawa, and the exponential one, and we parametrize them introducing a distortion parameter $b$ that quantifies the deviation from $\Lambda$CDM cosmology. Our analysis reveals that a small but non-zero deviation from $\Lambda$CDM cosmology is slightly favored, with the corresponding fittings exhibiting very efficient $AIC$ and $BIC$ Information Criteria values. Clearly, $f(R)$ gravity is consistent with observations, and it can serve as a candidate for modified gravity.

[50]  arXiv:1610.07523 [pdf, other]
Title: Seyfert 1 Composite Spectrum using SDSS Legacy Survey Data
Comments: 11 pages, 15 figures, 4 tables, accepted for publication in MNRAS. The median, geometric mean and ratio spectra are available online through MNRAS. The median spectra binned in redshift are also made available on the same page
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present a rest-frame composite spectrum for Seyfert 1 galaxies using spectra obtained from the DR12 release of the Sloan Digital Sky Survey (SDSS). The spectrum is constructed by combining data from a total of 10,112 galaxies, spanning a redshift range of 0 to 0.793. We produce an electronic table of the median and geometric mean composite Seyfert 1 spectrum. We measure the spectral index of the composite spec- trum, and compare it with that of the composite quasar spectrum. We also measure the flux and width of the strong emission lines present in the composite spectrum. We compare the entire spectrum with the quasar spectrum in the context of the AGN unification model. The two composite spectra match extremely well in the blue part of the spectrum, while there is an offset in flux in the red portion of the spectrum.

[51]  arXiv:1610.07529 [pdf, other]
Title: Radial acceleration relation from screening of fifth forces
Comments: 5 pages, 3 figures, revtex format
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)

We show that the radial acceleration relation for rotationally-supported galaxies may be explained, in the absence of cold dark matter, by a non-minimally coupled scalar field, whose fifth forces are partially screened on galactic scales by the symmetron mechanism. If realised in nature, this effect could have a significant impact on the inferred density of dark matter halos.

[52]  arXiv:1610.07533 [pdf, ps, other]
Title: EBL effect on the observation of multi-TeV flaring of 2009 from Markarian 501
Comments: 13 pages, 2 figures, latex. arXiv admin note: text overlap with arXiv:1501.00973
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Markarian 501 is a high-peaked BL Lacertae object and has undergone many major outburst since its discovery in 1996. As a part of the multiwavelength campaign, in the year 2009 this blazar was observed for 4.5 months from March 9 to August 1 and during the period April 17 to May 5 it was observed by both space and ground based observatories covering the entire electromagnetic spectrum. A very strong high energy $\gamma$-ray flare was observed on May 1 by Whipple telescope in the energy range 317 GeV to 5 TeV and the flux was about 10 times higher than the baseline flux. We use the photohadronic model complimented by the extragalactic background radiation (EBL) correction to this very high state flare and have shown that the EBL plays an important role in attenuating the very high energy flux even though Markarian 501 is in the local Universe.

[53]  arXiv:1610.07536 [pdf, other]
Title: Plasma dynamics in solar macrospicules from high-cadence EUV observations
Comments: Accepted for publication in A&A
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Macrospicules are relatively large spicule-like formations found mainly over the polar coronal holes when observing in the transition region spectral lines. In this study, we took advantage of the two short series of observations in the He II 304 \r{A} line obtained by the TESIS solar observatory with a cadence of up to 3.5 s to study the dynamics of macrospicules in unprecedented detail. We used a one-dimensional hydrodynamic method based on the assumption of their axial symmetry and on a simple radiative transfer model to reconstruct the evolution of the internal velocity field of 18 macrospicules from this dataset. Besides the internal dynamics, we studied the motion of the apparent end points of the same 18 macrospicules and found 15 of them to follow parabolic trajectories with high precision which correspond closely to the obtained velocity fields. We found that in a clear, unperturbed case these macrospicules move with a constant deceleration inconsistent with a purely ballistic motion and have roughly the same velocity along their entire axis, with the obtained decelerations typically ranging from 160 to 230 m/s^2, and initial velocities from 80 to 130 km/s. We also found a propagating acoustic wave for one of the macrospicules and a clear linear correlation between the initial velocities of the macrospicules and their decelerations, which indicates that they may be driven by magneto-acoustic shocks. Finally, we inverted our previous method by taking velocities from the parabolic fits to give rough estimates of the percentage of mass lost by 12 of the macrospicules. We found that typically from 10 to 30% of their observed mass fades out of the line (presumably being heated to higher coronal temperatures) with three exceptions of 50% and one of 80%.

[54]  arXiv:1610.07538 [pdf, ps, other]
Title: The $Λ$CDM simulations of Keller and Wadsley do not account for the MOND mass-discrepancy-acceleration relation
Authors: Mordehai Milgrom
Comments: 4 pages
Subjects: Astrophysics of Galaxies (astro-ph.GA); General Relativity and Quantum Cosmology (gr-qc)

Keller and Wadsley (2016) have smugly suggested, recently, that the end of MOND may be in view. This is based on their claim that their highly-restricted sample of $\Lambda$CDM-simulated galaxies are "consistent" with the observed MOND mass-discrepancy-acceleration relation (MDAR), in particular, with its recent update by McGaugh et al. (2016), based on the SPARC sample. From this they extrapolate to "$\Lambda$CDM is fully consistent" with the MDAR. I explain why these simulated galaxies do not show that $\Lambda$CDM accounts for the MDAR. a. Their sample of simulated galaxies contains only 18 high-mass galaxies, within a narrow range of one order of magnitude in baryonic mass, at the very high end of the observed, SPARC sample, which spans 4.5 orders of magnitude in mass. More importantly, the simulated sample has none of the low-mass, low-acceleration galaxies -- abundant in SPARC -- which encapsulate the crux and the nontrivial aspects of the predicted and observed MDAR. The low-acceleration part of the simulated MDAR is achieved, rather trivially, from the flattish-velocity-curve regions of the simulated high-mass galaxies. b. Half of the simulated galaxies have "wrong" rotation curves that differ greatly from any observed ones. This, does not prevent these wrong galaxies from lying on the observed MDAR (for trivial reasons, again). They, in fact, define the high-acceleration branch of the simulated MDAR. c. To boot, even if $\Lambda$CDM were made "consistent" with the MDAR through the elaborate adjustments that the simulations allow, this would not obviate MOND, which predicts much more than the MDAR.

[55]  arXiv:1610.07544 [pdf, ps, other]
Title: Magnetic flux density from the relative circular motion of stars and partially ionized gas in the Galaxy mid-plane vicinity
Comments: 10 pages, 10 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Observations suggest a slower stellar rotation relative to gas rotation in the outer part of the Milky Way Galaxy. This difference could be attributed to an interaction with the interstellar magnetic field. In a simple model, fields of order 10 micro Gauss are then required, consistently with the observed values. This coincidence suggests a tool for estimating magnetic fields in spiral galaxies. A North-South asymmetry in the rotation of gas in the Galaxy could be of magnetic origin too.

[56]  arXiv:1610.07552 [pdf, ps, other]
Title: The Solar Neighborhood XXXVIII. Results from the CTIO/SMARTS 0.9m: Trigonometric Parallaxes for 151 Nearby M Dwarf Systems
Comments: Accepted for publication to The Astronomical Journal; pre-print format
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We present 160 new trigonometric parallaxes for 151 M dwarf systems from the REsearch Consortium On Nearby Stars (RECONS) group's long-term astrometry/photometry program at the CTIO/SMARTS 0.9m telescope. Most systems (124 or 82%) are found to lie within 25 pc. The stars have 119 mas/yr < mu < 828 mas/yr and 3.85 < (V-K) < 8.47. Among these are 58 systems from the SuperCOSMOS-RECONS (SCR) search, discovered via our proper motion trawls of the SuperCOSMOS digitized archival photographic plates, while the remaining stars were suspected via photometric distance estimates to lie nearby. Sixteen are systems that are newly discovered via astrometric perturbations to be binaries, many of which are ideal for accurate mass determinations due to their proximity and orbital periods on the order of a decade. A variability analysis of the stars presented, two-thirds of which are new results, shows six of the stars to vary by more than 20 mmag. This effort brings the total number of parallaxes for M dwarf systems measured by RECONS to nearly 500 and increases by 26% the number of southern M dwarf systems with accurate trigonometric parallaxes placing them within 25 pc.

[57]  arXiv:1610.07558 [pdf, other]
Title: The Grism Lens-Amplified Survey from Space (GLASS) X. Sub-kpc resolution gas-phase metallicity maps at cosmic noon behind the Hubble Frontier Fields cluster MACS1149.6+2223
Comments: 26 pages, 14 figures, and 5 tables
Subjects: Astrophysics of Galaxies (astro-ph.GA)

(Abridged) We combine deep HST grism spectroscopy with a new Bayesian method to derive maps of gas-phase metallicity, nebular dust extinction, and star-formation rate for 10 star-forming galaxies at high redshift ($1.2<z<2.3$). Exploiting lensing magnification by the foreground cluster MACS1149.6+2223, we reach sub-kpc spatial resolution and push the stellar mass limit associated with such high-z spatially resolved measurements below $10^8M_\odot$ for the first time. Our maps exhibit diverse morphologies, indicative of various effects such as efficient radial mixing from tidal torques, rapid accretion of low-metallicity gas, etc., which can affect the gas and metallicity distributions in individual galaxies. Based upon an exhaustive sample of all existing sub-kpc metallicity gradients at high-z, we find that predictions given by analytical chemical evolution models assuming a relatively extended star-formation profile in the early disk formation phase can explain the majority of observed gradients, without involving galactic feedback or radial outflows. We observe a tentative correlation between stellar mass and metallicity gradient, consistent with the downsizing galaxy formation picture that more massive galaxies are more evolved into a later phase of disk growth, where they experience more coherent mass assembly at all radii and thus show shallower metallicity gradients. In addition, we compile a sample of homogeneously cross-calibrated integrated metallicity measurements spanning three orders of magnitude in stellar mass at $z\sim1.8$. We use this sample to study the mass-metallicity relation (MZR) and test the fundamental metallicity relation (FMR). The slope of the observed MZR can rule out the momentum-driven wind model at 3-$\sigma$ confidence level. We find no significant offset with respect to the FMR, taking into account the intrinsic scatter and measurement uncertainties.

[58]  arXiv:1610.07587 [pdf, other]
Title: Gamma Rays From Dark Matter Subhalos Revisited: Refining the Predictions and Constraints
Comments: 20 pages, 13 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA); High Energy Physics - Phenomenology (hep-ph)

Utilizing data from the ELVIS and Via Lactea-II simulations, we characterize the local dark matter subhalo population, and use this information to refine the predictions for the gamma-ray fluxes arising from annihilating dark matter in this class of objects. We find that the shapes of nearby subhalos are significantly altered by tidal effects, and are generally not well described by NFW density profiles, instead prefering power-law profiles with an exponential cutoff. From the subhalo candidates detected by the Fermi Gamma-Ray Space Telescope, we place limits on the dark matter annihilation cross section that are only modestly weaker than those based on observations of dwarf galaxies. We also calculate the fraction of observable subhalos that are predicted to be spatially extended at a level potentially discernible to Fermi.

[59]  arXiv:1610.07592 [pdf, other]
Title: The segregation of baryons and dark matter during halo assembly
Comments: 9 pages, 11 figures, submitted to MNRAS, for a movie of the halo discussed in Appendix B, see this http URL
Subjects: Astrophysics of Galaxies (astro-ph.GA)

The standard galaxy formation theory assumes that baryons and dark matter are initially well-mixed before becoming segregated due to radiative cooling. We use non-radiative hydrodynamical simulations to explicitly examine this assumption and find that baryons and dark matter can also be segregated during the build-up of the halo. As a result, baryons in many haloes do not originate from the same Lagrangian region as the dark matter. When using the fraction of corresponding dark matter and gas particles in the initial conditions (the "paired fraction") as a proxy of the dark matter and gas segregation strength of a halo, on average about $25$ percent of the baryonic and dark matter of the final halo are segregated in the initial conditions. A consequence of this effect is that the baryons and dark matter of the same halo initially experience different tidal torques and thus their angular momentum vectors are often misaligned. This is at odds with the assumption of the standard galaxy formation model, and challenges the precision of some semi-analytical approaches which utilize dark matter halo merger trees to infer properties of gas associated to dark matter haloes.