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Chemical history at $z \ge 2.0$: first results from the Magellan+Keck survey of Lyman limit systems

Published online by Cambridge University Press:  06 October 2005

John M. O'Meara
Affiliation:
Massachusetts Institute of Technology, Cambridge, MA 02139
S. Burles
Affiliation:
Massachusetts Institute of Technology, Cambridge, MA 02139
J. X. Prochaska
Affiliation:
UCO Lick Observatory, The University of California, Santa Cruz
G. Prochter
Affiliation:
UCO Lick Observatory, The University of California, Santa Cruz
R. Bernstein
Affiliation:
Astronomy Department, University of Michigan
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Abstract

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We present a measurement of $\left[\rm{O}/\rm{Fe}\right]$ versus $\left[\rm{Fe}/\rm{H}\right]$ in the $z>2$ IGM derived from a sample of 23 Lyman Limit systems whose column density lies in the range $19.0\le\log N_{HI}\le 20.2$ cm$^{-2}$. The systems span a metallicity range of $-2.70 \le \left[\rm{Fe}/\rm{H}\right]\le -0.50$, allowing for a direct comparison with similar studies of stars within the Milky Way. Although the Lyman Limit systems can be highly ionised, the effects of ionisation on the determination of $\left[\rm{O}/\rm{Fe}\right]$ is minor for most of the systems in the sample. The data appear to show a decrease in $\left[\rm{O}/\rm{Fe}\right]$ with increasing metallicity with an approximate slope of $m\simeq-0.55$. We also determine a best fit power law slope of $\alpha=-1.86 \pm 0.2$ to the column density distribution $f_{HI}(N)$ for $19.0 \le\log N_{HI}\le 20.2$ cm$^{-2}$.

Type
Contributed Papers
Copyright
© 2005 International Astronomical Union