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The Keck + Magellan Survey for Lyman Limit Absorption. III. Sample Definition and Column Density Measurements

Prochaska, J.X.; O'Meara, J.M.; Fumagalli, M.; Bernstein, R.A.; Burles, S.M.

The Keck + Magellan Survey for Lyman Limit Absorption. III. Sample Definition and Column Density Measurements Thumbnail


Authors

J.X. Prochaska

J.M. O'Meara

R.A. Bernstein

S.M. Burles



Abstract

We present an absorption-line survey of optically thick gas clouds—Lyman Limit Systems (LLSs)—observed at high dispersion with spectrometers on the Keck and Magellan telescopes. We measure column densities of neutral hydrogen ${N}_{{\rm{H}}\;{\rm{I}}}$ and associated metal-line transitions for 157 LLSs at ${z}_{\mathrm{LLS}}=1.76-4.39$ restricted to ${10}^{17.3}\;{\mathrm{cm}}^{-2}\leqslant {N}_{{\rm{H}}\;{\rm{I}}}\lt {10}^{20.3}\;{\mathrm{cm}}^{-2}.$ An empirical analysis of ionic ratios indicates an increasing ionization state of the gas with decreasing ${N}_{{\rm{H}}\;{\rm{I}}}$ and that the majority of LLSs are highly ionized, confirming previous expectations. The Si+/H0 ratio spans nearly four orders of magnitude, implying a large dispersion in the gas metallicity. Fewer than 5% of these LLSs have no positive detection of a metal transition; by $z\sim 3,$ nearly all gas that is dense enough to exhibit a very high Lyman limit opacity has previously been polluted by heavy elements. We add new measurements to the small subset of LLS (≈5%–10%) that may have super-solar abundances. High Si+/Fe+ ratios suggest an α-enhanced medium, whereas the Si+/C+ ratios do not exhibit the super-solar enhancement inferred previously for the Lyα forest.

Citation

Prochaska, J., O'Meara, J., Fumagalli, M., Bernstein, R., & Burles, S. (2015). The Keck + Magellan Survey for Lyman Limit Absorption. III. Sample Definition and Column Density Measurements. Astrophysical Journal Supplement, 221(1), https://doi.org/10.1088/0067-0049/221/1/2

Journal Article Type Article
Acceptance Date Jun 4, 2015
Publication Date Nov 1, 2015
Deposit Date Oct 25, 2015
Publicly Available Date Mar 28, 2024
Journal Astrophysical Journal Supplement
Print ISSN 0067-0049
Electronic ISSN 1538-4365
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 221
Issue 1
DOI https://doi.org/10.1088/0067-0049/221/1/2

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Copyright Statement
© 2015. The American Astronomical Society. All rights reserved.





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