The Connection between a Lyman Limit System, a very strong OVI Absorber, and Galaxies at z~0.203

TL;DR

This study investigates a very strong OVI absorber and a Lyman limit system at z~0.203, revealing their connection to nearby galaxies and the nature of the gas, including metallicity, ionization state, and possible origins.

Contribution

It provides the first detailed analysis linking a strong OVI absorber and a Lyman limit system to specific galaxy interactions and environments at low redshift.

Findings

The LLS has metallicity [Z/H]=-0.6 and is nearly fully photoionized.

The OVI absorber is collisionally ionized at T~(3-10)x10^5 K.

Galaxies within 2 Mpc are associated with the absorbers, indicating a galactic origin.

Abstract

With a column density log N(OVI) = 14.95+/-0.05, the OVI absorber at z_abs~0.2028 observed toward the QSO PKS0312-77 (z_em=0.223) is the strongest yet detected at z<0.5. At nearly identical redshift (z_abs=0.2026), we also identify a Lyman limit system (LLS, log N(HI)=18.22). Combining FUV and NUV spectra of PKS0312-77 with optical observations of galaxies in the surrounding field (15'x32'), we present an analysis of these absorbers and their connection to galaxies. The observed OI/HI ratio and photoionization modelling of other low ions indicate the metallicity of the LLS is [Z/H]_LLS=-0.6 and that the LLS is nearly 100% photoionized. In contrast, the OVI-bearing gas is collisionally ionized at T~(3-10)x10^5 K as derived from the high-ion ratios and profile broadenings. Our galaxy survey reveals 13 (0.3<L/L*<1.6) galaxies at \rho<2 h^{-1}_{70} Mpc and |\delta v|<1100 km/s from the LLS. A probable origin for the LLS is debris from a galaxy merger, which led to a 0.7L* galaxy ([Z/H]_gal=+0.15) at\rho~38 h^{-1}_{70} kpc. Outflow from this galaxy may also be responsible for the supersolar ([Z/H]_abs=+0.15), fully ionized absorber at z_abs=0.2018 (-190 km/s from the LLS). The hot OVI absorber likely probes coronal gas about the 0.7 L* galaxy and/or (~0.1 keV) intragroup gas of a spiral-rich system. The association of other strong OVI absorbers with LLS suggests they trace galactic and not intergalactic structures.