We use cookies to ensure that we give you the best experience on our website. By continuing to browse this repository, you give consent for essential cookies to be used. You can read more about our Privacy and Cookie Policy.

Durham Research Online
You are in:

# The rapid decline in metallicity of damped Lyα systems at z ~ 5.

Rafelski, M. and Neeleman, M. and Fumagalli, M. and Wolfe, A.M. and Prochaska, J.X. (2014) 'The rapid decline in metallicity of damped Lyα systems at z ~ 5.', Astrophysical journal letters., 782 (2). L29.

## Abstract

We present evidence that the cosmological mean metallicity of neutral atomic hydrogen gas shows a sudden decrease at z > 4.7 down to $\langle {Z}\rangle =-2.03^{+0.09}_{-0.11}$, which is 6σ deviant from that predicted by a linear fit to the data at lower redshifts. This measurement is made possible by the chemical abundance measurements of eight new damped Lyα (DLA) systems at z > 4.7 observed with the Echellette Spectrograph and Imager on the Keck II Telescope, doubling the number of measurements at z > 4.7 to 16. Possible explanations for this sudden decrease in metallicity include a change in the physical processes that enrich the neutral gas within disks, or an increase of the covering factor of neutral gas outside disks due to a lower ultraviolet radiation field and higher density at high redshift. The later possibility would result in a new population of presumably lower metallicity DLAs, with an increased contribution to the DLA population at higher redshifts resulting in a reduced mean metallicity. Furthermore, we provide evidence of a possible decrease at z > 4.7 in the comoving metal mass density of DLAs, ρmetals(z)DLA, which is flat out to z ~ 4.3. Such a decrease is expected, as otherwise most of the metals from star-forming galaxies would reside in DLAs by z ~ 6. While the metallicity is decreasing at high redshift, the contribution of DLAs to the total metal budget of the universe increases with redshift, with DLAs at z ~ 4.3 accounting for ~20% as many metals as produced by Lyman break galaxies.

Item Type: Article Galaxies: abundances, Galaxies: evolution, Galaxies: high-redshift, Galaxies: ISM, Quasars: absorption lines. (VoR) Version of Record Download PDF (1034Kb) Peer-reviewed http://dx.doi.org/10.1088/2041-8205/782/2/L29 © 2014. The American Astronomical Society. All rights reserved. 15 January 2014 03 July 2014 05 February 2014 No date available