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Description
The diffuse material filling the regions around the luminous parts of galaxies, the circumgalactic medium (CGM), is crucial to regulating galaxy evolution. In this project, we use a sample of two-quasar pairs that have small angular separations on the sky, so that one sightline probes a damped Lyα system (DLA) with a redshift between zabs = 1.57 − 3.54, while the other sightline probes the diffuse CGM at a specific transverse proper distance ranging from R⊥ = 25 − 284 kpc. DLAs are a type of quasar absorption line system with large column densities of HI (log(NHI) > 20.3 cm−2) and are thought to trace galaxies with halo masses 1010 M. Mh . 1012 M. We study the column densities of HI gas, as well as various metals, for 34 systems. We report a low incidence (10%) of high column density (log NHI > 20.1 cm−2) gas in these halos, suggesting that DLAs have small radii (< 25 kpc). For ions associated with cooler gas (T ∼ 104 K) we measure column densities lower than in the DLA sightlines at low transverse distances (< 25 kpc), while the more highly ionized metal lines (tracing T ∼ 105 K material) have column densities near the levels exhibited by the DLA within R⊥ < 150 kpc. We measure covering fractions within R⊥ < 150 kpc from the DLA for SiII of fc(log(NSiII) > 14.45 cm−2) = 9% and for CIV fc(log(NCIV) > 13.91 cm−2) = 42%. This is suggestive of a warm, ionized halo containing isolated and dense clumps of cool gas. Using these column densities, we estimate the metallicities for the DLAs to be approximately 2 dex below solar. Additional analysis is needed to correctly constrain the metallicities of the CGM. Finally, we measure the kinematics of cool and warm gas in the halos of DLAs. We detect gas at large line of sight velocities (> 200 km/s relative to zabs) in the CGM of DLAs, which is unbound assuming halo masses of . 1011 M and could therefore contribute to the enrichment of the surrounding intergalactic medium.
