Constraining the Size of the Circumgalactic Medium Using the Transverse Autocorrelation Function of C IV Absorbers in Paired Quasar Spectra

Abstract

The circumgalactic medium (CGM) plays a vital role in the formation and evolution of galaxies, acting as a lifeline between galaxies and the surrounding intergalactic medium. In this study, we leverage a unique sample of quasar pairs to investigate the properties of the CGM with absorption line tomography. We present a new sample of medium-resolution Keck/ESI, Magellan/MagE, and VLT/XSHOOTER spectra of 29 quasar pairs at redshift 2 < z < 3. We supplement the sample with additional spectra of 32 pairs from the literature, creating a catalog of 61 quasar pairs with angular separations between 1.″7 and 132.″9 and projected physical separations (r _⊥) between 14 kpc and 887 kpc. We construct a catalog of 906 metal-line absorption doublets of C IV (λλ1548, 1550) with equivalent widths ranging from 6 m Å ≤ W _r,1550 ≤ 2053 m Å. The best-fit linear model to the log-space equivalent width frequency distribution ( $\mathrm{log}f({W}_{r})=m\mathrm{log}({W}_{r})+b$ ) of the sample yields coefficients of m = -1.44 ± 0.16 and b = -0.43 ± 0.16. To constrain the projected extent of C IV, we calculate the transverse autocorrelation function. The flattening of the autocorrelation function at low r _⊥ provides a lower limit for the coherence length of the metal enriched CGM-on the order of 200 h ^-1 comoving kpc. This physical size constraint allows us to refine our understanding of the metals in the CGM, where the extent of C IV in the CGM depends on gas flows, feedback, timescale of metal injection and mixing, and the mass of the host galaxies.