On the Metallicities and Kinematics of the Circumgalactic Media of Damped Ly$\alpha$ Systems at $z\sim 2.5$

Abstract

We use medium- and high-resolution spectroscopy of close pairs of quasars to analyze the circumgalactic medium (CGM) surrounding 32 damped Ly$\alpha$ absorption systems (DLAs). The primary quasar sightline in each pair probes an intervening DLA in the redshift range $1.6<z_{\text{abs}}<3.5$, such that the secondary sightline probes absorption from Ly$\alpha$ and a large suite of metal-line transitions (including $\mathrm{OI}$, $\mathrm{CII}$, $\mathrm{CIV}$, $\mathrm{SiII}$, and $\mathrm{SiIV}$) in the DLA host galaxy's CGM at transverse distances $24\text{kpc}\le R_{\perp }\le 284\mathrm{kpc}$. Analysis of Ly$\alpha$ in the CGM sightlines shows an anti-correlation between $R_{\perp }$ and $\mathrm{HI}$ column density ($N_{\text{HI}}$) with 99.8$\%$ confidence, similar to that observed around luminous galaxies. The incidences of $\mathrm{CII}$ and $\mathrm{SiII}$ with $N>10^{13}\mathrm{c}{\mathrm{m}}^{-2}$ within 100 kpc of DLAs are larger by $2\sigma$ than those measured in the CGM of Lyman break galaxies (C${}_f(N_{\text{CII}})>0.89$ and C${}_f(N_{\text{SiII}})=0.75_{-0.17}^{+0.12}$). Metallicity constraints derived from ionic ratios for nine CGM systems with negligible ionization corrections and $N_{\text{HI}}>10^{18.5}\mathrm{c}{\mathrm{m}}^{-2}$ show a significant degree of scatter (with metallicities/limits across the range $-2.06\lesssim \log Z/Z_{\odot }\lesssim -0.75$), suggesting inhomogeneity in the metal distribution in these environments. Velocity widths of $\text{CIV}\lambda 1548$ and low-ionization metal species in the DLA vs. CGM sightlines are strongly ($>2\sigma$) correlated, suggesting they trace the potential well of the host halo over $R_{\perp }\lesssim 300$ kpc scales. At the same time, velocity centroids for $\text{CIV}\lambda 1548$ differ in DLA vs. CGM sightlines by $>100\mathrm{km}{\mathrm{s}}^{-1}$ for $\sim 50\%$ of velocity components, but few components have velocities that would exceed the escape velocity assuming dark matter host halos of $\ge 10^{12}{M}_{\odot }$.

44 pages, 21 Figures, 5 Tables, accepted for publication in ApJ

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• The galaxy counterpart and environment of the dusty Damped Lyman-alpha Absorber at z=2.226 towards Q1218+0832
• The multiple coherence scales of C IV at cosmic noon