05/11/2012

Metallicities, dust and molecular content of a QSO-Damped Lyman-α system reaching log N (H i) = 22: An analog to GRB-DLAs

R. Guimarães, P. Noterdaeme, P. Petitjean, C. Ledoux, R. Srianand, S. Lopez, H. Rahmani
(Submitted on 10 May 2012)

We present the elemental abundance and H2 content measurements of a Damped Lyman-{\alpha} (DLA) system with an extremely large H i column density, log N(H i) (cm-2) = 22.0+/-0.10, at zabs = 3.287 towards the QSO SDSS J 081634+144612. We measure column densities of H2, C i, C i^*, Zn ii, Fe ii, Cr ii, Ni ii and Si ii from a high signal-to-noise and high spectral resolution VLT-UVES spectrum. The overall metallicity of the system is [Zn/H] = -1.10 +/- 0.10 relative to solar. Two molecular hydrogen absorption components are seen at z = 3.28667 and 3.28742 (a velocity separation of \approx 52 km s-1) in rotational levels up to J = 3. We derive a total H2 column density of log N(H2) (cm-2) = 18.66 and a mean molecular fraction of f = 2N(H2)/[2N(H2) + N(H i)] = 10-3.04+/-0.37, typical of known H2-bearing DLA systems. From the observed abundance ratios we conclude that dust is present in the Interstellar Medium (ISM) of this galaxy, with a enhanced abundance in the H2-bearing clouds. However, the total amount of dust along the line of sight is not large and does not produce any significant reddening of the background QSO. The physical conditions in the H2-bearing clouds are constrained directly from the column densities of H2 in different rotational levels, C i and C i^* . The kinetic temperature is found to be T = 75 K and the particle density lies in the range nH = 50-80 cm-3 . The neutral hydrogen column density of this DLA is similar to the mean H i column density of DLAs observed at the redshift of {\gamma}-ray bursts (GRBs). We explore the relationship between GRB-DLAs and high column density end of QSO-DLAs finding that the properties (metallicity and depletion) of DLAs with log N(H i) > 21.5 in the two populations do not appear to be significantly different.

Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:1205.2322v1 [astro-ph.CO]

Probing the low-redshift star formation rate as a function of metallicity through the local environments of type II supernovae

R. Stoll, J. L. Prieto, K. Z. Stanek, R. W. Pogge
(Submitted on 10 May 2012)

Type II SNe can be used as a star formation tracer to probe the metallicity distribution of global low-redshift star formation. We present oxygen and iron abundance distributions of type II supernova progenitor regions that avoid many previous sources of bias, and can serve as a standard of comparison for properly observationally evaluating how different classes of supernovae depend on progenitor metallicity. In contrast to previous supernova host metallicity studies, this sample is homogeneous and is drawn from an areal rather than a targeted survey, so supernovae in the lowest-mass galaxies are not excluded. We spectroscopically measure the gas-phase oxygen abundance near a representative subsample of the hosts of type II supernovae from the first-year Palomar Transient Factory (PTF) supernova search. The median metallicity is 12+log(O/H) = 8.65 and the median host galaxy stellar mass from fits to SDSS photometry is 10^9.9 solar masses. Though iron abundance is more central to the evolution of massive stars than oxygen abundance, it cannot be measured directly in extragalactic HII regions. Using the relationship between iron and oxygen abundances found for Milky Way disk, bulge, and halo stars, we can translate our distribution of type II SN environments as a function of oxygen abundance into an estimate of the iron abundance, and find the median [Fe/H] = -0.60.

Comments: 20 pages, 15 figures. For electronic versions of the data tables, see this http URL For a brief video explaining the key results of this paper, see this http URL
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:1205.2338v1 [astro-ph.CO]
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