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

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 $\log N(HI)/c{m}^{-2}\approx 16.8$ (partial Lyman limit) while the absorber towards the other sightline has $N(HI)\approx 2$ 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 $\pm 250km{s}^{-1}$ 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${}_{\odot }$.

20 pages, 12 figures, 5 tables, Accepted for publication in MNRAS

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• The relationship between gas and galaxies at z<1 using the Q0107 quasar triplet
• Modelling gas around galaxy pairs and groups using the Q0107 quasar triplet