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

TL;DR

This study uses quasar pair spectra to measure the size of the circumgalactic medium's C IV-enriched gas, finding it extends at least 200 h^{-1} comoving kpc, which informs galaxy evolution models.

Contribution

It introduces a new analysis of quasar pair spectra to constrain the physical extent of C IV in the CGM, refining previous size estimates.

Findings

C IV absorption features are correlated up to at least 200 h^{-1} comoving kpc.

The equivalent width distribution follows a linear model in log-space.

The size of the C IV-enriched CGM is influenced by gas flows, feedback, and galaxy mass.

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 (IGM). 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 ($r_\perp$) between 14 kpc and 887 kpc. We construct a catalog of 906 metal-line absorption doublets of C IV ($\lambda\lambda 1548, 1550$) with equivalent widths ranging from 6 m{\AA} $\leq W_{r, 1550} \leq 2053$ m{\AA}. The best fit linear model to the log-space equivalent width frequency distribution ($\log f(W_r) = m\log(W_{r}) + b$) of the sample yields coefficients of $m=-1.44\pm0.16$ and $b=-0.43\pm0.16$. To constrain the projected extent of C IV, we calculate the transverse autocorrelation function. The flattening of the autocorrelation function at low $r_\perp$ 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.