The Cosmic Evolution of the Metallicity Distribution of Ionized Gas Traced by Lyman Limit Systems

Abstract

(2016) 'The cosmic evolution of the metallicity distribution of ionized gas traced by Lyman limit systems.', Astrophysical journal., Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. ), which are probed of the interface regions between the intergalactic medium (IGM) and galaxies. We study 31 H Iselected pLLSs and LLSs at < < z 2.3 3.3 observed with Keck/HIRES in absorption against background QSOs. We compare the column densities of metal ions to H I and use photoionization models to assess the metallicity. The metallicity distribution of the pLLSs/LLSs at < < z 2.3 3.3 is consistent with a unimodal distribution peaking atThe metallicity distribution of these absorbers therefore evolves markedly with z since at  z 1 it is bimodal with peaks atThere is a substantial fraction (25%-41%) of pLLSs/LLSs with metallicities well below those of damped Lyα absorbers (DLAs) at any studied z from  z 1 toz 2-4, implying reservoirs of metal-poor, cool, dense gas in the IGM/galaxy interface at all z. However, the gas probed by pLLSs and LLSs is rarely pristine, with a fraction of 3%-18% for pLLSs/LLSs withWe find C/α enhancement in several pLLSs and LLSs in the metallicity range, where C/α is 2-5 times larger than observed in Galactic metal-poor stars or high-redshift DLAs at similar metallicities. This is likely caused by preferential ejection of carbon from metal-poor galaxies into their surroundings.

Quasar 2175 Å dust absorbers – II. Correlation analysis and relationship with other absorption line systems

“…SubDLAs have been known to have higher mean metallicity than DLAs Khare et al 2007;Meiring et al 2009), and the [Zn/H] measurements in Figure 4 demonstrate the same trend with the inclusion of our data: the mean [Zn/H] for subDLAs is approximately solar while it is sub-solar for DLAs. Recent studies of more Lyman limit systems, however, show that although there exists a population of high metallicity super Lyman limit systems (or sub-DLAs), the average metallicity of subDLAs is probably similar or even lower than that of DLAs Lehner et al 2016). The 2DAs have logN(H i) values that range from subDLAs to DLAs and have systematically higher [Zn/H] at each logN(H i).…”

Gas Accretion via Lyman Limit Systems

“…Several independent groups have assessed the systematic errors connected to these ionization models (Howk et al 2009;Lehner et al 2013Lehner et al , 2016Crighton et al 2015;Fumagalli et al 2016b;Wotta et al 2016). For example, Wotta et al (2016) used HM12 (Haardt & Madau 2012) to estimate the metallicities of 10 LLSs at z < 1 from Lehner et al (2013) that were initially modeled with HM05.…”

“…The same selection criteria and analyses of the pLLSs and LLSs are applied at z < 1 and 2.3 < z < 3.3 by Lehner et al (2013) (and also Wotta et al 2016) and Lehner et al (2016), respectively, which allow for a direct comparison between the two samples as displayed in Figs. 3 and 4.…”

“…Thanks to large archives of good quality (in particular high resolution) spectra of both low and high z QSOs, we can now study the cosmic evolution of the H I- Fig. 4 Metallicity as a function of the H I column density for absorbers at z < 1 (top, results from Lehner et al 2013;Wotta et al 2016 and references therein) to 2.3 < z < 3.3 (bottom, results from Lehner et al 2016 and references therein, and see also the main text). Note that the metallicityscale in both panels is the same for direct comparison.…”

“…1 To measure N HI in pLLSs/LLSs, two methods are available. 1) left: we can measure the optical depth at the Lyman limit where τ LL ∝ N HI (these are low-resolution COS G140L spectra from Wotta et al 2016; 2) right: we fit a model to the Lyman series to derive N HI (these are normalized Keck HIRES profiles in the redshift frame of the pLLS at z LLS ∼ 3 from Lehner et al 2016). tically thick to Lyman continuum radiation, absorbing the UV radiation at λ ≤ 912 A. Empirically characterizing the UV background has been a scientific driver for studying LLSs as well as their potential connection to galaxies (e.g., Tytler 1982;Sargent et al 1989;Bahcall et al 1993;Lanzetta et al 1995;O'Meara et al 2007;Prochaska et al 2010;Ribaudo et al 2011a). While pLLSs and LLSs can be readily detected in low resolution spectra and their H I column densities can be estimated directly from the optical depth at the Lyman limit (see Fig.…”