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A. M. Sebastian

Publications and source records attributed to A. M. Sebastian.

2 recordsLinked to original sources

Connecting CGM enrichment with Lyman alpha emitters at 2.9 < z < 6.7

We present the results of a blind search for Lyman $\alpha$ emitters (LAEs) in three deep archival $z\sim6$ quasar fields from VLT/MUSE using state-of-the-art detection algorithms. We explore their connection with absorbers-particularly C IV and Mg II-in the circumgalactic medium (CGM) from the E-XQR-30 survey. We detect 156 LAEs at $2.9<z<6.7$ with luminosities ranging from log $L[\text{ergs}^{-1}]=$ 41.3 to 43.2. We find 34 and 14 galaxy associations with C IV and Mg II absorption respectively at $3.4<z<5.8$ within a line of sight velocity window of $\pm1000~\text{km}^{-1}$ and impact parameter of $<250$ pkpc. These systems have a weak anti-correlation with respect to the absorber strength-impact parameter relation. No Mg II systems are found within the virial radii of any LAE while four C IV absorbers are located within the virial radii of an LAE suggesting that low ionisation gas has a lower covering fraction. The LAEs have mild overdensity ratios of 1.7 and 1.9 around C IV and Mg II respectively. The stellar mass upper limits of $\text{log}~M_*<10.7~\text{M}_\odot$ estimated using Keck/NIRC2 imaging indicate that a low-mass, faint population of galaxies pollutes the CGM with metals. This paper serves as a pilot analysis for the forthcoming REQUIEM survey, an ESO Large Program on high redshift deep quasar fields.

astro-ph.GA

E-XQR-30: Evidence for an Increase in the Ionization State of Metal Absorbers from z~6 to z~2

We investigate the evolution of the ionization state of metal-enriched gas in and around galaxies near the epoch of reionization using a sample of 488 metal absorption systems at 4.3<z<6.3 from the E-XQR-30 survey. We classify the absorption systems based on whether they display only low-ionization absorption (CII, SiII, MgII), only high-ionization absorption (CIV, SiIV), or both. The percentage of low-ionization-only systems decreases from 24% at $z\sim$6 to 2% at $z\sim$4.3, whilst the fraction of high-ionization-only systems increases from 52% to 82%. For mixed absorbers (with both low and high ionization absorption), we use the column density ratios log(N_CII/N_CIV) and log(N_SiII/N_SiIV) to quantify the average ionization as a function of redshift. The log(N_SiII/N_SiIV) ratio does not change significantly over 5$\lesssim z \lesssim$6.3. We combine the E-XQR-30 log(N_CII/N_CIV) measurements with literature measurements at $z\sim$2-4 and find that the log(N_CII/N_CIV) ratio declines by a factor of $\sim$20 between $z\sim$6 and $z\sim$2. To explore possible drivers of this evolution, we run photoionization models of gas slabs illuminated by a uniform UV background at fixed density, metallicity and HI column density. We find that the increase in the ionization state of metal absorbers towards lower redshifts can likely be explained by some combination of 1) an increase in the metallicity of CIV-absorbing gas and 2) a decrease in the typical HI column densities of the absorbing gas, driven by the declining cosmic mean density and a rapid rise in the strength of the UV background during the final stages of reionization.

astro-ph.GA