MUSE Analysis of Gas around Galaxies (MAGG) – II: metal-enriched halo gas around z ∼ 1 galaxies

Abstract

We present a study of the metal-enriched cool halo gas traced by Mg ii absorption around 228 galaxies at z ∼ 0.8 − 1.5 within 28 quasar fields from the MUSE Analysis of Gas around Galaxies (MAGG) survey. We observe no significant evolution in the Mg ii equivalent width versus impact parameter relation and in the Mg ii covering fraction compared to surveys at z ≲ 0.5. The stellar mass, along with distance from galaxy centre, appears to be the dominant factor influencing the Mg ii absorption around galaxies. With a sample that is 90% complete down to a star formation rate of ≈0.1 $\rm M_\odot yr^{-1}$PLXINSERT-, and up to impact parameters ≈250 − 350 kpc from quasars, we find that the majority ($67^{+12}_{-15}$% or 14/21) of the Mg ii absorption systems are associated with more than one galaxy. The complex distribution of metals in these richer environments adds substantial scatter to previously-reported correlations. Multiple galaxy associations show on average five times stronger absorption and three times higher covering fraction within twice the virial radius than isolated galaxies. The dependence of Mg ii absorption on galaxy properties disfavours the scenario in which a widespread intra-group medium dominates the observed absorption. This leaves instead gravitational interactions among group members or hydrodynamic interactions of the galaxy haloes with the intra-group medium as favoured mechanisms to explain the observed enhancement in the Mg ii absorption strength and cross section in rich environments.

Metal-enriched halo gas across galaxy overdensities over the last 10 billion years

“…Next, we derived the stellar mass and star formation rate (SFR) of the sources using the Monte Carlo Spectro-Photometric Fitter (MC-SPF; Fossati et al 2018). We follow the procedure described in Fossati et al (2019b) and Dutta et al (2020). In brief, we use stellar population models from Bruzual & Charlot (2003) at solar metallicity, nebular emission lines from the models of Byler et al (2018), and the initial mass function (IMF) from Chabrier (2003).…”

“…For example, the Mg II doublet lines have long been used to trace the cool (T ∼ 10 4 K) and low-ionization (ionization potential, IP = 15.0 eV) gas (e.g. Lanzetta & Bowen 1990;Steidel & Sargent 1992;Churchill et al 2000;Chen et al 2010;Nielsen, Churchill & Kacprzak 2013;Zhu & Ménard 2013;Dutta et al 2020), while the C IV doublet lines on the other hand have been used extensively to trace the potentially warmer (T ∼ 10 5 K) and high-ionization (IP = 64.5 eV) gas (e.g. Sargent, Boksenberg & Steidel 1988;Chen, Lanzetta & Webb 2001;Schaye et al 2003;Cooksey et al 2013;Bordoloi et al 2014;Burchett et al 2016).…”

“…Further, there have been studies of the cool gas traced by Mg II absorption in individual groups and clusters (Whiting, Webster & Francis 2006;Lopez et al 2008;Kacprzak, Murphy & Churchill 2010;Gauthier 2013). Recently, with the advent of widefield optical integral field unit (IFU) spectrographs like the Multi Unit Spectroscopic Explorer (MUSE; Bacon et al 2010) on the Very Large Telescope (VLT), there have been several identifications of groups associated with cool gas as traced by Mg II absorption (Bielby et al 2017a;Fumagalli et al 2017;Péroux et al 2017Péroux et al , 2019Chen et al 2019;Fossati et al 2019b;Dutta et al 2020;Hamanowicz et al 2020). With a more complete identification of the small-scale galaxy environment and the galaxy population down to a fixed flux limit across the entire field of view (FoV), such studies suggest that environmental interactions play a role in enhancing the cross-section of Mg II absorbing gas around galaxies in groups (Fossati et al 2019b;Dutta et al 2020).…”

“…In this work, we study gaseous haloes up to z ≈ 2 with a systematic focus on the galaxy environment, taking advantage of the large and complete galaxy surveys that are becoming available now in quasar fields. In particular, we use data from two large, independent surveys -the MUSE Analysis of Gas around Galaxies (MAGG; Dutta et al 2020;Lofthouse et al 2020;Fossati et al 2021) survey and the Quasar Sightline and Galaxy Evolution (QSAGE; Bielby et al 2019;Stott et al 2020) survey. The structure of this paper is as follows.…”

MUSE analysis of gas around galaxies (MAGG) – III. The gas and galaxy environment of z = 3–4.5 quasars

“…The main goal of MAGG is the study of the CGM of z = 3-4.5 star-forming galaxies in the surroundings of H I absorbers with log N H I 10 17 cm −2 (Lofthouse et al, in preparation). The rich MAGG data sets are further being utilized to study the cold CGM gas around z ∼ 1 galaxies (Dutta et al 2020), and near z = 3-4.5 quasars, which is the subject of this work.…”