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Title: The Bimodal Absorption System Imaging Campaign (BASIC). I. A Dual Population of Low-metallicity Absorbers at z < 1
Abstract

The bimodal absorption system imaging campaign (BASIC) aims to characterize the galaxy environments of a sample of 36 Hi-selected partial Lyman limit systems (pLLSs) and Lyman limit systems (LLSs) in 23 QSO fields atz≲ 1. These pLLSs/LLSs provide a unique sample of absorbers with unbiased and well-constrained metallicities, allowing us to explore the origins of metal-rich and low-metallicity circumgalactic medium (CGM) atz< 1. Here we present Keck/KCWI and Very Large Telescope/MUSE observations of 11 of these QSO fields (19 pLLSs) that we combine with Hubble Space Telescope/Advanced Camera for Surveys imaging to identify and characterize the absorber-associated galaxies at 0.16 ≲z≲ 0.84. We find 23 unique absorber-associated galaxies, with an average of one associated galaxy per absorber. For seven absorbers, all with <10% solar metallicities, we find no associated galaxies withlogM9.0withinρ/Rvirand ∣Δv∣/vesc≤ 1.5 with respect to the absorber. We do not find any strong correlations between the metallicities or Hicolumn densities of the gas and most of the galaxy properties, except for the stellar mass of the galaxies: the low-metallicity ([X/H] ≤ −1.4) systems have a probability of0.390.15+0.16for having a host galaxy withlogM9.0withinρ/Rvir≤ 1.5, while the higher metallicity absorbers have a probability of0.780.13+0.10. This implies metal-enriched pLLSs/LLSs atz< 1 are typically associated with the CGM of galaxies withlogM>9.0, whereas low-metallicity pLLSs/LLSs are found in more diverse locations, with one population arising in the CGM of galaxies and another more broadly distributed in overdense regions of the universe. Using absorbers not associated with galaxies, we estimate the unweighted geometric mean metallicity of the intergalactic medium to be [X/H] ≲ −2.1 atz< 1, which is lower than previously estimated.

 
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Award ID(s):
2044303
PAR ID:
10397511
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;
Publisher / Repository:
DOI PREFIX: 10.3847
Date Published:
Journal Name:
The Astrophysical Journal
Volume:
944
Issue:
1
ISSN:
0004-637X
Format(s):
Medium: X Size: Article No. 101
Size(s):
Article No. 101
Sponsoring Org:
National Science Foundation
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