O. Gnat - Tel-Aviv University

O. Gnat
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O. Gnat
Tel-Aviv University
Tel Aviv-Yafo

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Cosmology and Nongalactic Astrophysics (6)
Astrophysics (5)
High Energy Astrophysical Phenomena (5)
Astrophysics of Galaxies (2)
Instrumentation and Methods for Astrophysics (2)
Solar and Stellar Astrophysics (1)
Earth and Planetary Astrophysics (1)

Publications Authored By O. Gnat

With the advent of new wide-field, high-cadence optical transient surveys, our understanding of the diversity of core-collapse supernovae has grown tremendously in the last decade. However, the pre-supernova evolution of massive stars, that sets the physical backdrop to these violent events, is theoretically not well understood and difficult to probe observationally. Here we report the discovery of the supernova iPTF13dqy = SN 2013fs, a mere ~3 hr after explosion. Read More

Based on high-resolution, spatially resolved data of 10 z~2 star-forming galaxies from the SINS/zC-SINF survey and LUCI data for 12 additional galaxies, we probe the excitation properties of high-z galaxies and the impact of active galactic nuclei (AGN), shocks and photoionization. We explore how these spatially-resolved line ratios can inform our interpretation of integrated emission line ratios obtained at high redshift. Many of our galaxies fall in the `composite' region of the z~0 [NII]/Ha versus [OIII]/Hb diagnostic (BPT) diagram, between star-forming galaxies and those with AGN. Read More

We discuss recent improvements in the calculation of the radiative cooling in both collisionally and photo ionized plasmas. We are extending the spectral simulation code Cloudy so that as much as possible of the underlying atomic data is taken from external databases, some created by others, some developed by the Cloudy team. This paper focuses on recent changes in the treatment of many stages of ionization of iron, and discusses its extensions to other elements. Read More

There is a consensus that Type-Ia supernovae (SNe Ia) arise from the thermonuclear explosion of white dwarf stars that accrete matter from a binary companion. However, direct observation of SN Ia progenitors is lacking, and the precise nature of the binary companion remains uncertain. A temporal series of high-resolution optical spectra of the SN Ia PTF 11kx reveals a complex circumstellar environment that provides an unprecedentedly detailed view of the progenitor system. Read More

(Abridged). The optical light curve of some SNe may be powered by the outward diffusion of the energy deposited by the explosion shock in optically thick circumstellar matter (CSM). Recently, it was shown that the radiation-mediated and -dominated shock in an optically thick wind must transform into a collisionless shock and can produce hard X-rays. Read More

Affiliations: 1UA Madrid, 2HU Jerusalem, 3Tel Aviv University, 4HU Jerusalem, 5UA Madrid

Cold gas streaming along the dark-matter filaments of the cosmic web is predicted to be the major provider of resources for disc buildup, violent disk instability and star formation in massive galaxies in the early universe. We study to what extent these cold streams are traceable in the extended circum-galactic environment of galaxies via Ly alpha absorption and selected low ionisation metal absorption lines. We model the expected absorption signatures using high resolution zoom-in AMR cosmological simulations. Read More

It is widely recognized that nucleosynthetic output of the first, Population III supernovae was a catalyst defining the character of subsequent stellar generations. Most of the work on the earliest enrichment was carried out assuming that the first stars were extremely massive and that the associated supernovae were unusually energetic, enough to completely unbind the baryons in the host cosmic minihalo and disperse the synthesized metals into the intergalactic medium. Recent work, however, suggests that the first stars may in fact have been somewhat less massive, with a characteristic mass scale of a few tens of solar masses. Read More

We present ion-by-ion cooling efficiencies for low-density gas. We use Cloudy (ver. 08. Read More

I present computations of the integrated column densities produced in the post-shock cooling layers and in the radiative precursors of partially-cooled fast shocks as a function of the shock age. The results are applicable to the shock-heated warm/hot intergalactic medium (WHIM) which is expected to be a major baryonic reservoir, and contain a large fraction of the so-called "missing baryons". My computations indicate that readily observable amounts of intermediate and high ions, such as CIV, NV, and OVI are created in the precursors of young shocks, for which the shocked gas remains hot and difficult to observe. Read More

We present numerical computations of the equilibrium configurations of tidally-locked homogeneous binaries, rotating in circular orbits. Unlike the classical Roche approximations, we self-consistently account for the tidal and rotational deformations of both components, and relax the assumptions of ellipsoidal configurations and Keplerian rotation. We find numerical solutions for mass ratios q between 1e-3 and 1, starting at a small angular velocity for which tidal and rotational deformations are small, and following a sequence of increasing angular velocities. Read More

We present computations of the ionization structure and metal-absorption properties of thermally conductive interface layers that surround evaporating warm spherical clouds, embedded in a hot medium. We rely on the analytical formalism of Dalton & Balbus to calculate the temperature profile in the evaporating gas, and explicitly solve the time-dependent ionization equations for H, He, C, N, O, Si, and S in the interface. We include photoionization by an external field. Read More

Affiliations: 1Carnegie Observatories, 2Weizmann Institute, 3Caltech, 4Caltech, 5UC Berkeley, 6UC Berkeley, 7ESO, 8UC Berkeley, 9UC Berkeley, 10Texas, 11CfA, 12ESO, 13LBL, 14CfA, 15UCSC, 16Carnegie DTM, 17UC Berkeley, 18UBC Okanagan, 19MPE, 20Stockholm, 21MPA

Recent observations have revealed that some Type Ia supernovae exhibit narrow, time-variable Na I D absorption features. The origin of the absorbing material is controversial, but it may suggest the presence of circumstellar gas in the progenitor system prior to the explosion, with significant implications for the nature of the supernova progenitors. We present the third detection of such variable absorption, based on six epochs of high-resolution spectroscopy of the Type Ia supernova SN 2007le from Keck and the HET. Read More

In this paper we present computations of the integrated metal-ion column densities produced in the post-shock cooling layers behind fast, radiative shock-waves. For this purpose, we have constructed a new shock code that calculates the non-equilibrium ionization and cooling; follows the radiative transfer of the shock self-radiation through the post-shock cooling layers; takes into account the resulting photoionization and heating rates; follows the dynamics of the cooling gas; and self-consistently computes the initial photoionization state of the precursor gas. We discuss the shock structure and emitted radiation, and study the dependence on the shock velocity, magnetic field, and gas metallicity. Read More

We establish a simple model for the distribution of cold gas around L* galaxies using a large set of observational constraints on the properties of strong MgII absorber systems. Our analysis suggests that the halos of L* galaxies are filled with cool gaseous clouds having sizes of order 1kpc and densities of ~10^{-2} cm^{-3}. We then investigate the physical effects of cloud irradiation by a quasar and study the resulting spectral signatures. Read More

Affiliations: 1Tel-Aviv University, 2Tel-Aviv University
Category: Astrophysics

We present new computations of the equilibrium and non-equilibrium cooling efficiencies and ionization states for low-density radiatively cooling gas containing cosmic abundances of the elements H, He, C, N, O, Ne, Mg, Si, S, and Fe. We present results for gas temperatures between 1e4 and 1e8 K, assuming dust-free and optically thin conditions, and no external radiation. For non-equilibrium cooling we solve the coupled time-dependent ionization and energy loss equations for a radiating gas cooling from an initially hot, >5e6K equilibrium state, down to 1e4K. Read More

(Abridged) We present computations of the metals photoionization structures of pressure supported gas clouds in gravitationally dominant DM minihalos in the extended Galactic halo or LG environment. We consider low-metallicity (0.1-0. Read More

We present a radial-velocity study of the triple-lined system Gliese 644 and derive spectroscopic elements for the inner and outer orbits with periods of 2.9655 and 627 days. We also utilize old visual data, as well as modern speckle and adaptive optics observations, to derive a new astrometric solution for the outer orbit. Read More