Pair lines of sight observations of multiphase gas bearing OVI in a galaxy environment

Using HST/COS spectra of the twin quasar lines of sight Q 0107-025A & Q 0107-025B, we report on the physical properties, chemical abundances, and transverse sizes of a multiphase medium in a galaxy field at z = 0.399. The angular separation between the quasars corresponds to a physical separation of 520 kpc at the absorber redshift. The absorber towards Q 0107-025B is a partial Lyman limit system (pLLS) with log N(HI)/cm(-2) approximate to 16.8. The HI column density in the absorber along the other sightline is approximate to 2 orders of magnitude lower. The OVI along both sightlines have comparable column densities and broad b-values (b > 30 km s(-1)) whereas the low ionization lines are considerably narrower. The low ionization gas is inconsistent with the OVI when modelled assuming photoionization from the same phase. In both lines of sight, OVI and the broad HI coinciding, are best explained through collisional ionization in a cooling plasma with solar metallicity. Ionization models infer 1/10th solar metallicity for the pLLS and solar metallicity for the lower column density absorber along the other sightline. Within +/- 250 km s(-1) and 2 Mpc of projected distance from the sightlines 12 galaxies are identified, of which five are within 500 kpc. The twin sightlines are at normalized impact parameters of rho similar to 1.1R(vir), and rho similar to 0.8R(vir) from a M-* similar to 10(10.7) M-circle dot, L similar to 0.07L*, and star formation rate (SFR) < 0.1 M-circle dot yr(-1) galaxy, potentially probing its CGM (circumgalactic medium). The next closest in normalized separation are a dwarf galaxy with M-* similar to 10(8.7) M-circle dot, and SFR similar to 0.06 M-circle dot yr(-1), and an intermediate mass galaxy with M-* similar to 10(10.0) M-circle dot, and SFR similar to 3 M-circle dot yr(-1). Along both sightlines, OVI could be either tracing narrow transition temperature zones at the interface of low ionization gas and the hot halo of nearest galaxy, or a more spread-out warm component that could be gas bound to the circumgalactic halo or the intragroup medium. The latter scenarios lead to a warm gas mass limit of M greater than or similar to 4.5 x 10(9) M-circle dot.

Automated summary

This study presents the physical properties, chemical abundances, and transverse sizes of a multiphase medium in a galaxy field at z = 0.399 using HST/COS spectra of the twin quasar lines of sight Q 0107-025A & Q 0107-025B. The absorber towards Q 0107-025B is a partial Lyman limit system (pLLS) while the absorber along the other sightline has a lower HI column density. OVI and broad HI coinciding in both sightlines are best explained through collisional ionization in a cooling plasma with solar metallicity.