Quasars Probing Quasars VIII. The Physical Properties of the Cool Circumgalactic Medium Surrounding z ~ 2-3 Massive Galaxies Hosting Quasars

TL;DR

This study investigates the physical properties of the cool circumgalactic medium around z~2-3 quasar host galaxies, revealing extreme kinematics, significant enrichment, and complex ionization states, with implications for galaxy evolution.

Contribution

It provides the first detailed characterization of the cool CGM around high-redshift quasars, including kinematics, metallicity, and ionization, highlighting unique features not seen in other galaxy populations.

Findings

Extreme gas kinematics exceeding 500 km/s.

Median metallicity around -0.6 dex, enriched beyond virial radius.

Detection of peculiar features like fluorescent Ly-alpha emission and high electron density.

Abstract

We characterize the physical properties of the cool T ~10^4 K circumgalactic medium surrounding z ~2-3 quasar host galaxies, which are predicted to evolve into present day massive ellipticals. Using a statistical sample of 14 quasar pairs with projected separation < 300 kpc and high dispersion, high S/N spectra, we find extreme kinematics with low metal ion lines typically spanning ~ 500 km/s, exceeding any previously studied galactic population. The CGM is significantly enriched, even beyond the virial radius, with a median metallicity [M/H] ~ -0.6. The alpha/Fe abundance ratio is enhanced, suggesting that halo gas is primarily enriched by core-collapse supernovae. The projected cool gas mass within the virial radius is estimated to be 1.9*10^11 M_sun (R_\perp/160 kpc)^2, accounting for ~ 1/3 of the galaxy halo baryonic budget. The ionization state of CGM gas increases with projected distance from the foreground quasars, contrary to expectation if the quasar dominates the ionizing radiation flux. However, we also found peculiarities not exhibited in the CGM of other galaxy populations. In one absorption system, we may be detecting unresolved fluorescent Ly-alpha emission, and another system shows strong NV lines. Taken together these anomalies suggest that transverse sightlines are at least in some cases possibly illuminated. We also discovered a peculiar case where detection of the CII* fine structure line implies an electron density > 100 cm^-3 and subparsec scale gas clumps.