Pair lines of sight observations of multiphase gas bearing O\u2009vi in a galaxy environment

Abstract

Using HST /COS observations 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 gas in a multiple galaxy environment at z = 0.399 across a transverse separation of 520 kpc. The absorber towards Q 0107 − 025B has logN(H I)/cm ≈ 16.8 (partial Lyman limit) while the absorber towards the other sightline has N(H I) ≈ 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 ± 250 km s 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 ρ ∼ (1− 4) Rvir. 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 & 4.5× 10 M⊙.