%0 Generic %1 rafelski2013rapid %A Rafelski, Marc %A Neeleman, Marcel %A Fumagalli, Michele %A Wolfe, Arthur M. %A Prochaska, J. Xavier %D 2013 %K dlas evolution metallicity %T The Rapid Decline in Metallicity of Damped Ly-$\alpha$ Systems at $z\sim5$ %U http://arxiv.org/abs/1310.6042 %X We present evidence that the cosmological mean metallicity of neutral atomic hydrogen gas shows a sudden decrease at $z>4.7$ down to $< Z >=-2.03^+0.09_-0.11$, which is $6\sigma$ 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 8 new damped Ly-$\alpha$ (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. The sudden decrease in metallicity is possibly due to the lower ultra-violet radiation field and higher density at high redshift increasing the neutral fraction of gas inside halos, such as cold flows. This 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. While the comoving metal mass density of DLAs, $\rho_metals(z)_DLA$, is flat out to $z\sim4.3$, there is evidence of a possible decrease at $z>4.7$. Such a decrease is expected, as otherwise most of the metals from star-forming galaxies would reside in DLAs by $z\sim6$. 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 $z\sim4.3$ accounting for $\sim20$% as many metals as produced by Lyman break galaxies.

@misc{rafelski2013rapid, abstract = {We present evidence that the cosmological mean metallicity of neutral atomic hydrogen gas shows a sudden decrease at $z>4.7$ down to $< {\rm Z} >=-2.03^{+0.09}_{-0.11}$, which is $6\sigma$ 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 8 new damped Ly-$\alpha$ (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. The sudden decrease in metallicity is possibly due to the lower ultra-violet radiation field and higher density at high redshift increasing the neutral fraction of gas inside halos, such as cold flows. This 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. While the comoving metal mass density of DLAs, $\rho_{\rm metals}(z)_{\rm DLA}$, is flat out to $z\sim4.3$, there is evidence of a possible decrease at $z>4.7$. Such a decrease is expected, as otherwise most of the metals from star-forming galaxies would reside in DLAs by $z\sim6$. 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 $z\sim4.3$ accounting for $\sim20$% as many metals as produced by Lyman break galaxies.}, added-at = {2013-10-24T09:28:56.000+0200}, author = {Rafelski, Marc and Neeleman, Marcel and Fumagalli, Michele and Wolfe, Arthur M. and Prochaska, J. Xavier}, biburl = {https://www.bibsonomy.org/bibtex/249dc1889dc47bbf486d956b5f9d8fe34/miki}, description = {[1310.6042] The Rapid Decline in Metallicity of Damped Ly-$\alpha$ Systems at $z\sim5$}, interhash = {4e6e653d32f97a6ac368e87e86aa5060}, intrahash = {49dc1889dc47bbf486d956b5f9d8fe34}, keywords = {dlas evolution metallicity}, note = {cite arxiv:1310.6042Comment: 6 pages, 4 figures, submitted to ApJL}, timestamp = {2013-10-24T09:28:56.000+0200}, title = {The Rapid Decline in Metallicity of Damped Ly-$\alpha$ Systems at $z\sim5$}, url = {http://arxiv.org/abs/1310.6042}, year = 2013 }