Metal line emission from galaxy haloes at z~1

Abstract

We present a study of the metal-enriched halo gas, traced using Mg and [O ] emission lines, in two large, blind galaxy surveys conducted using Multi Unit Spectroscopic Explorer (MUSE) optical integral field unit observations, namely the MUSE Analysis of Gas around Galaxies (MAGG) and the MUSE Ultra Deep Field (MUDF). By stacking a sample of ≈600 galaxies with stellar masses M * ≈ 10 6−12 M (median M * ≈ 2 × 10 9 M ) at redshifts 𝑧 = 0.7 − 1.5 (median 𝑧 ≈ 1), we characterize for the first time the average metal line emission from a general population of galaxy haloes. The Mg and [O ] line emission extends farther out than the stellar continuum emission around galaxies, on average out to ≈25 kpc and ≈45 kpc, respectively, at a surface brightness (SB) level of 10 −20 erg s −1 cm −2 arcsec −2 . The radial profile of the Mg SB is shallower than that of the [O ], suggesting that the resonant Mg emission is affected by dust and radiative transfer effects. The [O ] to Mg SB ratio is ≈ 3 over ≈ 20 − 40 kpc, also indicating a significant in situ origin of the extended metal emission in the inner halo. The average profiles are intrinsically brighter by a factor ≈ 2 − 3 and more radially extended by a factor of ≈ 1.3 at 1.0 < 𝑧 ≤ 1.5 than at 0.7 ≤ 𝑧 ≤ 1.0. The average extent of the metal emission also increases independently with increasing stellar mass and in overdense group environments. When considering individual detections, we find extended [O ] emission up to ≈ 50 kpc around ≈ 30 − 40 percent of the group galaxies, and extended (≈ 30 − 40 kpc) Mg emission around two 𝑧 ≈ 1 quasars in groups, which could arise from outflows or environmental processes.