Pair Lines of Sight Observations of Multiphase Gas Bearing O VI in a Galaxy Environment

TL;DR

This study uses HST/COS observations of twin quasar sightlines to analyze the physical properties, metallicity, and distribution of multiphase gas, including O VI, in a galaxy environment at redshift 0.399, revealing insights into circumgalactic and intragroup media.

Contribution

It provides the first detailed analysis of multiphase, O VI-bearing gas across two sightlines separated by 520 kpc in a galaxy environment, highlighting collisional ionization processes.

Findings

O VI and broad H I are consistent with collisional ionization in a cooling plasma.

The metallicity varies from 1/10 solar in partial Lyman limit systems to solar in lower column density absorbers.

The warm gas mass in the circumgalactic environment is estimated to be at least 4.5 x 10^9 solar masses.

Abstract

Using $HST$/COS observations of the twin quasar lines of sight Q$0107-025$A $\&$ Q$0107-025$B, we report on the physical properties, chemical abundances and transverse sizes of gas in a multiple galaxy environment at $z = 0.399$ across a transverse separation of $520$ kpc. The absorber towards Q$0107-025$B has $\log N(H I)/cm^{-2} \approx 16.8$ (partial Lyman limit) while the absorber towards the other sightline has $N(H I) \approx 2$ dex lower. The O VI along both sightlines have comparable column densities and broad $b$-values, whereas the low ionization lines are considerably narrower. The low ionization gas is inconsistent with the O VI when modelled assuming photoionization in a single phase. Along both the lines-of-sight, O VI and coinciding broad H I are best explained through collisional ionization in a cooling plasma with solar metallicity. Ionization models infer $1/10$-th solar metallicity for the pLLS and solar metallicity for the lower column density absorber along the other sightline. Within $\pm~250~km~s^{-1}$ and $2$ Mpc of projected distance from the sightlines 12 galaxies are identified, of which 3 are within $300$ kpc. One of them is a dwarf galaxy while the other two are intermediate mass systems at impact parameters of $\rho \sim (1-4)R_{vir}$. The O VI along both lines-of-sight 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 gas bound to the circumgalactic halo/intragroup medium. This latter scenario leads to a warm gas mass limit of $M \gtrsim 4.5 \times 10^{9}$ M$_\odot$.