Probing the intra-group medium of a z = 0.28 galaxy group

We present new MUSE observations of a galaxy group probed by a background quasar. The quasar sightline passes between multiple z = 0.28 galaxies, whilst showing at the same redshift low-ionized metal line species, including Ca II, Mg I, Mg II and Fe II. Based on the galaxy redshifts measured from the MUSE data, we estimate the galaxies to be part of a small galaxy group with a halo mass of ≈6 × 10¹² M☉. We use the MUSE data to reveal the two-dimensional dynamical properties of the gas and stars in the group galaxies, and relate these to the absorber kinematics. With these data, we consider a number of scenarios for the nature of the gas probed by the sightline absorbers: a corotating gas halo associated with a single galaxy within the group; outflowing material from a single group member powered by recent star-formation; and cool dense gas associated with an intra-group medium. We find that the dynamics, galaxy impact parameters, star formation rates and the absorber strength suggest that the cool gas cannot be clearly associated with any single galaxy within the group. Instead, we find that the observations are consistent with a superposition of cool gas clouds originating with the observed galaxies as they fall into the group potential, and are now likely in the process of forming the intra-group medium.