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<inf>H</inf> ? 10?3 cm?3) parsec-scale cloud of solar or higher metallicity. The kinematically coincident higher ions are either from a more diffuse (n<inf>H</inf> ? 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 ? ? 200 kpc and separation |v| = 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. © 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society