The Role of Dense Circumgalactic Gas in Shaping Galaxies

This dissertation is composed of two projects that study the circumgalactic medium (CGM) of galaxies at z < 1, searching for connections between the gas in galaxy halos and their host galaxy properties. For galaxies to continue forming stars, they must accrete material that passes through the CGM in the form of large-scale inflows (recycling material or gas from the intergalactic medium, IGM) while also contending with large-scale outflows (winds escaping the galaxy disk). In this work, we investigate whether the CGM properties correlate with the galaxy properties using absorbers known as partial Lyman limit systems (pLLSs) and Lyman limit systems (LLSs) with 16.0 ≤ logNHI < 19.0 [cm^-2].

In Chapter 2, we present the bimodal absorption system imaging campaign (BASIC) which is an absorption-selected CGM survey at z < 1 aimed at understanding the types of galaxies that house absorbers of different metallicities. We use integral field unit observations to identify and characterize the host galaxies of absorbers that span a broad range (0.1−54% solar) in metallicity.

We present the red dead redemption (RDR) survey, composed of two samples, in Chapters 3 (RDR1) and 4 (RDR2). This galaxy-selected survey uses luminous red galaxies (LRGs, logM★ > 11 M⊙) at z ~ 0.5 to observationally test model predictions for cold-mode and hot-mode accretion into galaxy halos by determining the cool HI gas content in LRG halos and the metallicity of the absorbers we detect. RDR1 is an archival sample of QSO-LRG pairs with sightlines probing to ~Rvir; RDR2 is an HST Cycle 25 and archival sample of QSO-LRG pairs with sightlines probing to ~0.4Rvir in the halo.

Our findings show the CGM metallicity does not correlate with most of the host galaxy properties, with the exception of stellar mass. There is no mass where we do not find cool gas in the inner CGM of galaxy halos, and low-metallicity absorbers are found in halos of all masses. However, the majority of these absorbers are most likely associated with the IGM instead of galaxy halos.