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.
Description
[1310.6042] The Rapid Decline in Metallicity of Damped Ly-$\alpha$ Systems at $z\sim5$
%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
}