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

Abstract

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 with $\log N({{\rm H~}{\rm \small I}})/{\rm cm^{-2}}\approx 16.8$. The H i column density in the absorber along the other sightline is ≈2 orders of magnitude lower. The O vi 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 O vi when modelled assuming photoionization from the same phase. In both lines-of-sight, O vi and the broad H i coinciding, 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−1 and 2 Mpc of projected distance from the sightlines 12 galaxies are identified, of which 5 are within 500 kpc. The twin sightlines are at normalized impact parameters of ρ ∼ 1.1Rvir, and ρ ∼ 0.8Rvir from a M* ∼ 1010.7 M⊙, L ∼ 0.07L*, and SFR <0.1 M⊙ yr−1 galaxy, potentially probing its CGM. The next closest in normalized separation are a dwarf galaxy with M* ∼ 108.7 M⊙, and SFR ∼0.06 M⊙ yr−1, and an intermediate mass galaxy with M* ∼ 1010.0 M⊙, and SFR ∼3 M⊙ yr−1. Along both sightlines, O vi 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 leads to a warm gas mass limit of M ≳ 4.5 × 109 M⊙.

Modelling gas around galaxy pairs and groups using the Q0107 quasar triplet

“…Petry et al 2006;Crighton et al 2010), construction of the 2D 2point correlation functions of absorption in both H and O (Tejos et al 2014, hereafter T14, Finn et al 2016, and detailed radiative transfer modelling of a small number of absorbers (e.g. Muzahid 2014;Anshul et al 2021). Improvements to the available data, such as higher-resolution spectra of the three quasars, high-resolution imaging from the Hubble Space Telescope, and IFU observations of the field, have enabled our recent works extending these results.…”

“…Strong, metal-enriched absorption in G-399 lies at a velocity between the two large galaxies in this group. As discussed in Anshul et al (2021), this contains a warm component as well as a cooler gas phase. This is consistent with intra-group material, lying within 𝑟 𝑣𝑖𝑟 of the largest group galaxy, and could be tidal in origin.…”

“…A-56, A-69 and B-7 are the three galaxies within the HST image at z ≈ 0.399. The state of the gas causing absorption in the sightlines at this redshift is modelled in Anshul et al (2021); both sightlines feature transitions from multiple metal ions. The details are given in Table 5 and illustrated in Figure 4.…”

“…This may suggest that this material has been stripped from one of the galaxies, or that an outflow from one of the galaxies has been distorted by interaction with the CGM of the other such that it can no longer be fit by our toy models. Anshul et al (2021) find that the absorption in QSO-A is consistent with solar metallicity in both components, and use a two-Table 4. Summary of galaxy and absorber properties for group G-238.…”

The relationship between gas and galaxies at z<1 using the Q0107 quasar triplet

“…The other three systems exist in galaxy groups, where it is difficult to distinguish between tidal debris, virialized haloes, and warm outflows. More detailed ionization modelling of the absorption in two of these groups are described in Muzahid (2014) and Anshul et al (2021).…”