Solar-metallicity gas in the extended halo of a galaxy at z ∼ 0.12

Abstract

We present the detection and analysis of a weak low-ionization absorber at z = 0.121 22 along the sightline of the blazar PG 1424+240, using spectroscopic data from both HST/COS and STIS. The absorber is a weak Mg II analogue, with an incidence of weak C II and Si II, along with multicomponent C IV and O VI. The low ions are tracing a dense (n_H ∼ 10^-3 cm^-3) parsec-scale cloud of solar or higher metallicity. The kinematically coincident higher ions are either from a more diffuse (n_H ∼ 10^-5-10^-4 cm^-3) photoionized phase of kiloparsec-scale dimensions or are tracing a warm (T ∼ 2 × 10⁵ K) collisionally ionized transition temperature plasma layer. The absorber resides in a galaxy overdense region, with 18 luminous (>L*) galaxies within a projected radius of 5 Mpc and velocity of 750 km s^-1. The multiphase properties, high metallicity, and proximity to a 1.4L* galaxy, at ρ ∼ 200 kpc and separation |ΔV| = 11 km s^-1, favour the possibility of the absorption tracing circumgalactic gas. The absorber serves as an example of weak Mg II-O VI systems as a means to study multiphase high-velocity clouds in external galaxies.