MusE GAs FLOw and Wind (MEGAFLOW) XIII. Cool gas traced by MgII around isolated galaxies

TL;DR

This study investigates the distribution and properties of cool MgII-traced gas in the circumgalactic medium of isolated star-forming galaxies at redshifts 0.4 to 1.5, revealing its dependence on impact parameter, galaxy properties, and orientation.

Contribution

It provides new measurements of MgII covering fractions around isolated galaxies and explores their evolution and dependence on galaxy characteristics and orientation.

Findings

MgII covering fraction decreases with impact parameter.

Covering fraction is higher along the minor axis than the major axis.

The impact parameter for 50% covering fraction is about 50 kpc.

Abstract

The circumgalactic medium (CGM) is a key component needed to understand the physical processes governing the flows of gas around galaxies. Quantifying its evolution and its dependence on galaxy properties is particularly important for our understanding of accretion and feedback mechanisms. We select a volume-selected sample of 66 {\it isolated} star-forming galaxies (SFGs) at $0.4< z <1.5$ with $\log(M_\star/M_{\odot})> 9$ from the MusE GAs FLOw and Wind (MEGAFLOW) survey. Using MgII 2796,2803 absorptions in background quasars, we measure the covering fraction $f_c$ and quantify how the cool gas profile depends on galaxy properties (such as star-formation rate (SFR), stellar mass ($M_\star$) or azimuthal angle relative to the line of sight) and how these dependencies evolve with redshift. The MgII covering fraction of isolated galaxies is a strong function of impact parameter, and is steeper than previously reported. The impact parameter $b_{50}$ at which $f_c = $50\% is $b_{50}=50\pm7$kpc ($65\pm7$ kpc) for $W_r^{2796}>$0.5 \AA ($W_r^{2796}>0.1$ \AA), respectively. It is weakly correlated with SFR ($\propto$ SFR$^{0.08\pm0.09}$) and decreases with cosmic time ($\propto (1+z)^{0.8 \pm 0.7}$), contrary to the expectation of increasingly larger halos with time. The covering fraction is also higher along the minor axis than along the major axis at the $\approx 2 \sigma$ level. The CGM traced by \MgII{} is similar across the isolated galaxy population. Indeed, among the isolated galaxies with an impact parameter below 55 kpc, all have associated MgII absorption with $W_r^{2796}>$0.3\AA, resulting in a steep covering fraction $f_c(b)$.