A partial Lyman limit system tracing intragroup gas at z ≈ 0.8 towards HE 1003 + 0149

We present analysis of the galaxy environment and physical properties of a partial Lyman limit system at z = 0.83718 with H i and metal-line components closely separated in redshift space (|Δv| ≈ 400 km s ⁻¹ ) towards the background quasar HE 1003 + 0149. The HST/COS far-ultraviolet spectrum provides coverage of lines of oxygen ions from O i to O v. Comparison of observed spectral lines with synthetic profiles generated from Bayesian ionization modelling reveals the presence of two distinct gas phases in the absorbing medium. The low-ionization phase of the absorber has sub-solar metallicities (∼1/10 solar) with indications of [C/O] <0 in each of three components. The O iv and O v trace a more diffuse higher ionization medium with predicted H i column densities that are ≈2 dex lower. The quasar field observed with VLT/MUSE reveals three dwarf galaxies with stellar masses of M∗ ∼ 10 ⁸ –10 ⁹ M ⊙ , and with star formation rates of ≈0.5–1 M⊙ yr ⁻¹ , at projected separations of ρ/R vir ≈ 1.8–3.0 from the absorber. Over a wider field with projected proper separation of ≤5 Mpc and radial velocity offset of |Δv| ≤ 1000 km s ⁻¹ from the absorber, 21 more galaxies are identified in the VLT/VIMOS and Magellan deep galaxy redshift surveys, with 8 of them within 1 Mpc and 500 km s ⁻¹ , consistent with the line of sight penetrating a group of galaxies. The absorber presumably traces multiple phases of cool (T ∼ 10 ⁴ K) photoionized intragroup medium. The inferred [C/O] <0 hint at preferential enrichment from core-collapse supernovae, with such gas displaced from one or more of the nearby galaxies, and confined to the group medium.