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.

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: Oct 27, 2015
• 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
• Public URL: https://durham-repository.worktribe.com/output/1428108