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Unveiling the secrets of metallicity and massive star formation using DLAs along gamma-ray bursts.

Cucchiara, A. and Fumagalli, M. and Rafelski, M. and Kocevski, D. and Prochaska, J. X. and Cooke, R. J. and Becker, G. D. (2015) 'Unveiling the secrets of metallicity and massive star formation using DLAs along gamma-ray bursts.', Astrophysical journal., 804 (1). p. 51.


We present the largest, publicly available sample of damped Lyα systems (DLAs) along the lines of sight of Swift-discovered gamma-ray bursts (GRBs) in order to investigate the environmental properties of long GRB hosts in the z = 1.8–6 redshift range. Compared with the most recent quasar DLA sample (QSO-DLA), our analysis shows that GRB-DLAs probe a more metal-enriched environment at $z\gtrsim 3$, up to $[X/H]\sim -0.5$. In the z = 2–3 redshift range, despite the large number of lower limits, there are hints that the two populations may be more similar (only at a 90% significance level) than at higher redshifts. Also, at high-z, the GRB-DLA average metallicity seems to decline at a lower rate than the QSO-DLAs: GRB-DLA hosts may be polluted with metals at least as far as $\sim 2\;$ kpc from the GRB explosion site, probably due to previous star formation episodes and/or supernova explosions. This shallow metallicity trend, now extended up to $z\sim 5$, confirms previous results that GRB hosts are star-forming and have, on average, higher metallicities than the general QSO-DLA population. Finally, our host metallicity measurements are broadly consistent with the predictions derived from the hypothesis of two channels of GRB progenitors, one of which is mildly affected by a metallicity bias, although more data are needed to constrain the models at $z\gtrsim 4$.

Item Type:Article
Keywords:Galaxies: general, Galaxies: ISM, Gamma-ray burst: general, Quasars: absorption lines, Techniques: imaging spectroscopy.
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Publisher statement:© 2015. The American Astronomical Society. All rights reserved.
Date accepted:17 February 2015
Date deposited:28 May 2015
Date of first online publication:May 2015
Date first made open access:No date available

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