On the Metallicities and Kinematics of the Circumgalactic Media of Damped Lyα Systems at z ∼ 2.5*

Abstract

We use medium- and high-resolution spectroscopy of close pairs of quasars to analyze the circumgalactic medium (CGM) surrounding 32 damped Ly α absorption systems (DLAs). The primary quasar sightline in each pair probes an intervening DLA in the redshift range 1.6 < z abs < 3.5, such that the secondary sightline probes absorption from Ly α and a large suite of metal-line transitions (including O i , C ii , C iv , Si ii , and Si iv ) in the DLA host galaxy’s CGM at transverse distances 24 kpc ≤ R ⊥ ≤ 284 kpc. Analysis of Ly α in the CGM sightlines shows an anticorrelation between R ⊥ and H i column density ( N HI ) with 99.8% confidence, similar to that observed around luminous galaxies. The incidences of C ii and Si ii with N > 10 13 cm −2 within 100 kpc of DLAs are larger by 2 σ than those measured in the CGM of Lyman break galaxies (C f ( N C II ) > 0.89 and C f ( N Si II ) = 0.75 − 0.17 + 0.12 ). Metallicity constraints derived from ionic ratios for nine CGM systems with negligible ionization corrections and N HI > 10 18.5 cm −2 show a significant degree of scatter (with metallicities/limits across the range − 2.06 ≲ log Z / Z ⊙ ≲ − 0.75 ), suggesting inhomogeneity in the metal distribution in these environments. Velocity widths of C iv λ 1548 and low-ionization metal species in the DLA versus CGM sightlines are strongly (>2 σ ) correlated, suggesting that they trace the potential well of the host halo over R ⊥ ≲ 300 kpc scales. At the same time, velocity centroids for C iv λ 1548 differ in DLA versus CGM sightlines by >100 km s −1 for ∼50% of velocity components, but few components have velocities that would exceed the escape velocity assuming dark matter host halos of ≥10 12 M ⊙ .