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Buchner J.,Millenium Institute of Astrophysics | Buchner J.,University of Santiago de Chile | Schulze S.,Millenium Institute of Astrophysics | Schulze S.,University of Santiago de Chile | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2017

An important constraint for galaxy evolution models is how much gas resides in galaxies, in particular, at the peak of star formation z = 1-3.We attempt a novel approach by letting longduration gamma ray bursts (LGRBs) x-ray their host galaxies and deliver column densities to us. This requires a good understanding of the obscurer and biases introduced by incomplete follow-up observations.We analyse the X-ray afterglowof all 844 Swift LGRBs to date for their column density NH. To derive the population properties, we propagate all uncertainties in a consistent Bayesian methodology. The NH distribution covers the 1020-23 cm-2 range and shows no evolutionary effect. Higher obscurations, e.g. Compton-thick columns, could have been detected but are not observed. The NH distribution is consistent with sources randomly populating a ellipsoidal gas cloud of major axis N major H = 1023cm-2 with 0.22 dex intrinsic scatter between objects. The unbiased SHOALS survey of afterglows and hosts allows us to constrain the relation between Spitzer-derived stellarmasses and X-ray derived column densities NH.We find a well-constrained power-law relation of NH = 1021.7 cm-2 × (M*/109.5M⊙)1/3, with 0.5 dex intrinsic scatter between objects. The Milky Way and the Magellanic clouds also follow this relation. From the geometry of the obscurer, its stellar mass dependence and comparison with local galaxies, we conclude that LGRBs are primarily obscured by galaxy-scale gas. Ray tracing of simulated Illustris galaxies reveals a relation of the same normalization, but a steeper stellar-mass dependence and mild redshift evolution. Our new approach provides valuable insight into the gas residing in high-redshift galaxies. © 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Buchner J.,Millenium Institute of Astrophysics | Buchner J.,University of Santiago de Chile | Bauer F.E.,Millenium Institute of Astrophysics | Bauer F.E.,University of Santiago de Chile | Bauer F.E.,Space Science Institute
Monthly Notices of the Royal Astronomical Society | Year: 2017

The 'torus' obscurer of active galactic nuclei (AGN) is poorly understood in terms of its density, sub-structure and physical mechanisms. Large X-ray surveys provide model boundary constraints, for both Compton-thin and Compton-thick levels of obscuration, as obscured fractions aremean covering factors fcov. However, a major remaining uncertainty is host-galaxy obscuration. In Paper I, we discovered a relation of NH ∝ M* 1/3 for the obscuration of galaxyscale gas. Here, we apply this observational relation to the AGN population, and find that galaxy-scale gas is responsible for a luminosity-independent fraction of Compton-thin AGN, but does not produce Compton-thick columns. With the host-galaxy obscuration understood, we present a model of the remaining nuclear obscurer, which is consistent with a range of observations. Our radiation-lifted torus model consists of a Compton-thick component (fcov ~ 35 per cent) and a Compton-thin component (fcov ~ 40 per cent), which depends on both black hole mass and luminosity. This provides a useful summary of observational constraints for torus modellers who attempt to reproduce this behaviour. It can also be employed as a sub-grid recipe in cosmological simulations that do not resolve the torus. We also investigate host-galaxy X-ray obscuration inside cosmological, hydrodynamic simulations (Evolution and Assembly of Galaxies and their Environment; Illustris). The obscuration from ray-traced galaxy gas can agree with observations, but is highly sensitive to the chosen feedback assumptions. © 2016 The Authors.

Jimenez N.,University of St. Andrews | Jimenez N.,CONICET | Jimenez N.,University of Trieste | Jimenez N.,Institute D Estudis Espacials Of Catalonia Ieec | And 6 more authors.
Astrophysical Journal | Year: 2015

The nature of the Type Ia supernova (SN Ia) progenitors remains uncertain. This is a major issue for galaxy evolution models since both chemical and energetic feedback plays a major role in the gas dynamics, star formation, and therefore the overall stellar evolution. The progenitor models for the SNe Ia available in the literature propose different distributions for regulating the explosion times of these events. These functions are known as the delay time distributions (DTDs). This work is the first one in a series of papers aiming at studying five different DTDs for SNe Ia. Here we implement and analyze the single-degenerate (SD) scenario in galaxies dominated by a rapid quenching of the star formation, displaying the majority of the stars concentrated in the bulge component. We find a good fit to both the present observed SN Ia rates in spheroidal-dominated galaxies and the [O/Fe] ratios shown by the bulge of the Milky Way. Additionally, the SD scenario is found to reproduce a correlation between the specific SN Ia rate and the specific star formation rate (sSFR), which closely resembles the observational trend, at variance with previous works. Our results suggest that SN Ia observations in galaxies with very low and very high sSFRs can help to impose more stringent constraints on the DTDs and therefore on SN Ia progenitors. © 2015. The American Astronomical Society. All rights reserved.

Kodric M.,Ludwig Maximilians University of Munich | Kodric M.,Max Planck Institute for Extraterrestrial Physics | Riffeser A.,Ludwig Maximilians University of Munich | Riffeser A.,Max Planck Institute for Extraterrestrial Physics | And 16 more authors.
Astrophysical Journal | Year: 2015

We present the largest M31 near-infrared (F110W (close to J band), F160W (H band)) Cepheid sample so far. The sample consists of 371 Cepheids with photometry obtained from the Hubble Space Telescope PHAT program. The sample of 319 fundamental mode Cepheids, 16 first overtone Cepheids, and 36 type II Cepheids was identified using the median absolute deviation outlier rejection method we develop here. This method does not rely on priors and allows us to obtain this clean Cepheid sample without rejecting a large fraction of Cepheids. The obtained period-luminosity relations (PLRs) have a very small dispersion, i.e., 0.155 mag in F160W, despite using random phased observations. This remarkably small dispersion allows us to determine that the PLRs are significantly better described by a broken slope at 10 days than a linear slope. The use of our sample as an anchor to determine the Hubble constant gives a 3.2% larger Hubble constant compared to the Riess et al. sample. © 2015. The American Astronomical Society. All rights reserved.

Barbuy B.,University of Sao Paulo | Chiappini C.,Leibniz Institute for Astrophysics Potsdam | Cantelli E.,University of Sao Paulo | Depagne E.,Leibniz Institute for Astrophysics Potsdam | And 13 more authors.
Astronomy and Astrophysics | Year: 2014

Context. The [Sr/Ba] and [Y/Ba] scatter observed in some galactic halo stars that are very metal-poor and in a few individual stars of the oldest known Milky Way globular cluster NGC 6522 have been interpreted as evidence of early enrichment by massive fast-rotating stars (spinstars). Because NGC 6522 is a bulge globular cluster, the suggestion was that not only the very-metal poor halo stars, but also bulge stars at [Fe/H] ~-1 could be used as probes of the stellar nucleosynthesis signatures from the earlier generations of massive stars, but at much higher metallicity. For the bulge the suggestions were based on early spectra available for stars in NGC 6522, with a medium resolution of R ~ 22 000 and a moderate signal-to-noise ratio. Aims. The main purpose of this study is to re-analyse the NGC 6522 stars reported previously by using new high-resolution (R ~ 45 000) and high signal-to-noise spectra (S/N > 100). We aim at re-deriving their stellar parameters and elemental ratios, in particular the abundances of the neutron-capture s-process-dominated elements such as Sr, Y, Zr, La, and Ba, and of the r-element Eu. Methods. High-resolution spectra of four giants belonging to the bulge globular cluster NGC 6522 were obtained at the 8m VLT UT2-Kueyen telescope with the UVES spectrograph in FLAMES-UVES configuration. The spectroscopic parameters were derived based on the excitation and ionization equilibrium of Fea i and Fe ii. Results. Our analysis confirms a metallicity [Fe/H] =-0.95 ± 0.15 for NGC 6522 and the overabundance of the studied stars in Eu (with +0.2 < [Eu/Fe] < + 0.4) and alpha-elements O and Mg. The neutron-capture s-element-dominated Sr, Y, Zr, Ba, and La now show less pronounced variations from star to star. Enhancements are in the range 0.0 < [Sr/Fe] < +0.4, +0.23 < [Y/Fe] < +0.43, 0.0 < [Zr/Fe] < +0.4, 0.0 < [La/Fe] < +0.35, and 0.05 < [Ba/Fe] < +0.55. Conclusions. The very high overabundances of [Y/Fe] previously reported for the four studied stars is not confirmed with the new high-quality spectra. The moderate enhancement in [Sr/Fe] previously reported for one of the re-studied stars is confirmed, but the strong enhancements of this ratio for the other two stars are not confirmed. Despite the moderate enhancements found for the neutron-capture s-element-dominated species, none of the four stars studied here show positive values for all [Sr/Ba], [Y/Ba] and [Zr/Ba] ratios. The re-studied stars are now compatible not only with the interpretation that the s-process enhancements in these very old stars are due to spinstars, but also with alternative models such as mass transfer from s-process-rich AGB stars. Note, however, that when our results are interpreted in the context of more extended datasets from the literature, the spinstar scenario still seems to be favoured. © 2014 ESO.

Herve A.,Czech Republic Astronomical Institute | Herve A.,Montpellier University | Martins F.,Montpellier University | Chene A.-N.,Gemini Observatory | And 3 more authors.
New Astronomy | Year: 2016

The evolution of massive stars is only partly understood. Observational constraints can be obtained from the study of massive stars located in young massive clusters. The ESO Public Survey "VISTA Variables in the Vía Lácteá (VVV)" discovered several new clusters hosting massive stars. We present an analysis of massive stars in four of these new clusters. Our aim is to provide constraints on stellar evolution and to better understand the relation between different types of massive stars. We use the radiative transfer code CMFGEN to analyse K-band spectra of twelve stars with spectral types ranging from O and B to WN and WC. We derive the stellar parameters of all targets as well as surface abundances for a subset of them. In the Hertzsprung-Russell diagram, the Wolf-Rayet stars are more luminous or hotter than the O stars. From the log(C/N)-log(C/He) diagram, we show quantitatively that WN stars are more chemically evolved than O stars, WC stars being more evolved than WN stars. Mass loss rates among Wolf-Rayet stars are a factor of 10 larger than for O stars, in agreement with previous findings. © 2015 Elsevier B.V. All rights reserved.

Bauer F.E.,University of Santiago de Chile | Bauer F.E.,Millenium Institute of Astrophysics | Bauer F.E.,Space Science Institute | Arevalo P.,EMBIGGEN Anillo | And 32 more authors.
Astrophysical Journal | Year: 2015

We report on high-energy X-ray observations of the Compton-thick Seyfert 2 galaxy NGC 1068 with NuSTAR, which provide the best constraints to date on its >10 keV spectral shape. The NuSTAR data are consistent with those from past and current instruments to within cross-calibration uncertainties, and we find no strong continuum or line variability over the past two decades, which is in line with its X-ray classification as a reflection-dominated Compton-thick active galactic nucleus. The combined NuSTAR, Chandra, XMM-Newton, and Swift BAT spectral data set offers new insights into the complex secondary emission seen instead of the completely obscured transmitted nuclear continuum. The critical combination of the high signal-to-noise NuSTAR data and the decomposition of the nuclear and extranuclear emission with Chandra allow us to break several model degeneracies and greatly aid physical interpretation. When modeled as a monolithic (i.e., a single NH) reflector, none of the common Compton reflection models are able to match the neutral fluorescence lines and broad spectral shape of the Compton reflection hump without requiring unrealistic physical parameters (e.g., large Fe overabundances, inconsistent viewing angles, or poor fits to the spatially resolved spectra). A multi-component reflector with three distinct column densities (e.g., with best-fit values of NH of 1.4 × 1023, 5.0 × 1024, and 1025 cm-2) provides a more reasonable fit to the spectral lines and Compton hump, with near-solar Fe abundances. In this model, the higher NH component provides the bulk of the flux to the Compton hump, while the lower NH component produces much of the line emission, effectively decoupling two key features of Compton reflection. We find that ≈30% of the neutral Fe K-α line flux arises from >2″ (≈140 pc) and is clearly extended, implying that a significant fraction (and perhaps most) of the <10 keV reflected component arises from regions well outside a parsec-scale torus. These results likely have ramifications for the interpretation of Compton-thick spectra from observations with poorer signal-to-noise and/or more distant objects. © 2015. The American Astronomical Society. All rights reserved..

Garrido H.E.,Catholic University of the Holy Conception | Garrido H.E.,University of Concepción | Mennickent R.E.,University of Concepción | Djurasevic G.,Astronomical Observatory | And 6 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2016

We investigate the luminous star ELHC 10 located in the bar of the Large Magellanic Cloud (LMC), concluding that it is a SB1 long-period eclipsing binary where the main eclipse is produced by an opaque structure hiding the secondary star. For the more luminous component we determine an effective temperature of 6500±250 K, log g=1.0±0.5 and luminosity 5970 L⊙. From the radial velocities of their photospheric lines, we calculate a mass function of 7.37 ± 0.55 M⊙. Besides Balmer and forbidden NII emission, we find splitting of metallic lines, characterized by strong discrete absorption components, alternatively seen at the blue and red side of the photospheric spectrum. These observations hardly can be interpreted in terms of an structured atmosphere but might reflect mass streams in an interacting binary. The primary shows signatures of s-process nucleosynthesis and might be a low-mass post-asymptotic giant branch star with a rare evolutionary past if the binary is semidetached. The peak separation and constancy of radial velocity in Hα suggest that most of the Balmer emission comes from a circumbinary disc. © 2016 The Authors.

Calderon D.,University of Santiago de Chile | Bauer F.E.,University of Santiago de Chile | Bauer F.E.,Millenium Institute of Astrophysics | Bauer F.E.,Space Science Institute | And 7 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2016

We present constraints on the molecular outflows in a sample of five hyperluminous infrared galaxiesusing Herschel observations of the OH doublet at 119 μm. We have detected the OH doublet in three cases: one purely in emission and two purely in absorption. The observed emission profile has a significant blueshifted wing suggesting the possibility of tracing an outflow. Out of the two absorption profiles, one seems to be consistent with the systemic velocity while the other clearly indicates the presence of a molecular outflow whose maximum velocity is about ~1500 km s-1. Our analysis shows that this system is in general agreement with previous results on ultraluminous infrared galaxies and QSOs, whose outflow velocities do not seem to correlate with stellar masses or starburst luminosities (star formation rates). Instead, the galaxy outflow likely arises from an embedded active galactic nuclei. © 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Helminiak K.G.,Japan National Astronomical Observatory | Helminiak K.G.,Nicolaus Copernicus Astronomical Center | Graczyk D.,Millenium Institute of Astrophysics | Graczyk D.,University of Concepción | And 18 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2015

We present the first full orbital and physical analysis of HD 187669, recognized by the All- Sky Automated Survey (ASAS) as the eclipsing binary ASAS J195222-3233.7.We combined multi-band photometry from the ASAS and SuperWASP public archives and 0.41-m PROMPT robotic telescopes with our high-precision radial velocities from theHARPSspectrograph. Two different approaches were used for the analysis: (1) fitting to all data simultaneously with the WDcode and (2) analysing each light curve (with JKTEBOP) and radial velocities separately and combining the partial results at the end. This system also shows a total primary (deeper) eclipse, lasting for about 6 d. A spectrum obtained during this eclipse was used to perform atmospheric analysis with the MOOG and SME codes to constrain the physical parameters of the secondary. We found that ASAS J195222-3233.7 is a double-lined spectroscopic binary composed of two evolved, late-type giants, with masses of M1 = 1.504 ± 0.004 and M2 = 1.505 ± 0.004 M⊙, and radii of R1 = 11.33 ± 0.28 and R2 = 22.62 ± 0.50 R⊙. It is slightly less metal abundant than the Sun, and has a P = 88.39 d orbit. Its properties are well reproduced by a 2.38-Gyr isochrone, and thanks to the metallicity estimation from the totality spectrum and high precision of the masses, it was possible to constrain the age down to 0.1Gyr. It is the first so evolved Galactic eclipsing binary measured with such good accuracy, and as such it is a unique benchmark for studying the late stages of stellar evolution. © 2015 The Authors.

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