The COS CGM Compendium (CCC). I: Survey Design and Initial Results
Nicolas Lehner, Christopher B. Wotta, J. Christopher Howk, John M., O'Meara, Benjamin D. Oppenheimer, and Kathy L. Cooksey

TL;DR
This survey of HI-selected absorbers at z<1 using Hubble's COS instrument reveals that most gas is ionized, photoionized, and exhibits a wide metallicity range, with very little pristine gas present.
Contribution
First comprehensive survey of HI-selected absorbers at z<1 with detailed metallicity and ionization analysis using COS data.
Findings
Gas is largely ionized and photoionized.
Wide metallicity range from solar to less than 1% solar.
Pristine gas is rare at z<1.
Abstract
We present a neutral hydrogen-selected absorption-line survey of gas with HI column densities 15<log N(HI)<19 at z<1 using the Cosmic Origins Spectrograph on the Hubble Space Telescope. Our main aim is to determine the metallicity distribution of these absorbers. Our sample consists of 224 absorbers selected on the basis of their HI absorption strength. Here we discuss the properties of our survey and the immediate empirical results. We find singly and doubly ionized metal species and HI typically have similar velocity profiles, implying they probe gas in the same or similar environments. The column density ionic ratios (e.g., CII/CIII, OI/CII) indicate the gas in these absorbers is largely ionized, and the ionization conditions are quite comparable across the sampled N(HI) range. The Doppler parameters of the HI imply T<50,000 K on average, consistent with the gas being photoionized.…
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