Quasars Probing Quasars VII. The Pinnacle of the Cool Circumgalactic Medium Surrounds Massive z~2 Galaxies

TL;DR

This study reveals that the circumgalactic medium around z~2 quasars contains a vast, metal-rich, cool gas reservoir with high covering fractions, primarily influenced by halo mass, and significantly contributes to strong absorption features observed in the universe.

Contribution

It provides the first detailed measurement of the cool CGM around massive z~2 quasars, highlighting its extent, metal content, and relation to halo mass, surpassing previous galaxy observations.

Findings

High covering fraction of CII absorption (0.73±0.10) around quasars.

Estimated metal mass in the CGM exceeds 10^8 solar masses.

The cool CGM accounts for most strong MgII absorption along random sightlines.

Abstract

We survey the incidence and absorption strength of the metal-line transitions CII 1334 and CIV from the circumgalactic medium (CGM) surrounding z~2 quasars, which act as signposts for massive dark matter halos M_halo~10^12.5 Msun. On scales of the virial radius (Mvir~160kpc), we measure a high covering fraction fC=0.73+/-0.10 to strong CII absorption (rest equivalent width W1334>0.2A), implying a massive reservoir of cool (T~10^4K) metal enriched gas. We conservatively estimate a metal mass exceeding 10^8 Msun. We propose these metals trace enrichment of the incipient intragroup/intracluster medium that these halos eventually inhabit. This cool CGM around quasars is the pinnacle amongst galaxies observed at all epochs, as regards covering fraction and average equivalent width of HI Lya and low-ion metal absorption. We argue that the properties of this cool CGM primarily reflect the halo mass, and that other factors such as feedback, star-formation rate, and accretion from the intergalactic medium are secondary. We further estimate, that the CGM of massive, z~2 galaxies accounts for the majority of strong MgII absorption along random quasar sightlines. Lastly, we detect an excess of strong CIV absorption (W1548>0.3A) over random incidence to 1Mpc physical impact parameter and measure the quasar-CIV cross-correlation function: xi(r)=(r/r0)^-g with r0 = 7.5Mpc and g=1.7. Consistent with previous work on larger scales, we infer that this highly ionized CIV gas traces massive (10^12 Msun) halos.