MUSEQuBES: The column density, covering fraction, and mass of OVI-bearing gas in and around low-redshift galaxies

TL;DR

This study investigates the properties of OVI-bearing gas around low-mass galaxies at low redshift, revealing how OVI column density, covering fraction, and mass vary with galaxy stellar mass and environment, highlighting the processes influencing circumgalactic gas.

Contribution

It provides the first comprehensive analysis of OVI gas in low-mass galaxies using MUSEQuBES data, combining observations with literature to understand ionization mechanisms and gas distribution.

Findings

OVI column density peaks at stellar mass ~10^9.5 Msun.

Dwarf galaxies have an average OVI mass of ~10^5.2 Msun.

OVI covering fraction drops significantly outside the virial radius.

Abstract

We present a study of OVI-bearing gas around 247 low-mass (median log(M*/Msun)~8.7) galaxies at low redshifts (0.1 < z < 0.7) using background quasars as part of the MUSE Quasar-fields Blind Emitters Survey (MUSEQuBES). We find that the average OVI column density, ${\rm log}_{10}<N({\rm OVI})/{\rm cm}^{-2}>$ = $14.14^{+0.09}_{-0.10}$, measured within the virial radius for our sample, is significantly lower than for L_* galaxies. Combining 253 star-forming galaxies (mostly more massive) from the literature with 176 star-forming galaxies from MUSEQuBES, we find that both <N(OVI)> and the average covering fraction peak at log(M*/Msun)~9.5. The virial temperature corresponding to this stellar mass is ideal for OVI production via collisional ionization. However, we argue that photoionization and/or non-equilibrium processes are necessary to produce the OVI associated with low-mass, dwarf galaxies (log(M*/Msun)<9). The average OVI mass within the virial radius of dwarf galaxies is measured to be $10^{5.2_{-0.1}^{+0.1}}$ Msun. The characteristic normalized impact parameter at which the OVI covering fraction drops to half of its peak value is the largest (~1.1) for galaxies with stellar mass log(M*/Msun)~9.5. We report the presence of a highly ionized metal floor with ${\rm log}_{10}(N({\rm OVI})/{\rm cm}^{-2}) = 13.2$ outside the virial radius of dwarf galaxies inferred from median spectral stacking.