The MUSE eXtremely deep field: first panoramic view of an Mg ̄ II emitting intragroup medium

Using the exquisite data from the MUSE eXtremely Deep Field (MXDF), we report the discovery of an Mg ̄II emission nebula with an area above a 2I significance level of 1000 proper kpc2. This provides the first panoramic view of the spatial distribution of magnesium in the intragroup medium of a low-mass group of five star-forming galaxies at za" =a" 1.31. The galaxy group members are separated by less than 50 physical kpc in projection and ~120 km sa1 in velocity space. The most massive galaxy has a stellar mass of 109.35a Ma and shows an Mg ̄II P-Cygni line profile, indicating the presence of an outflow, which is consistent with the spatially resolved spectral analysis showing ~+120 km sa1 shift of the Mg ̄II emission lines with respect to the systemic redshift. The other galaxies are less massive and only show Mg ̄II in emission. The detected Mg ̄II nebula has a maximal projected extent of ~70 kpc, including a low-surface-brightness (~2 A- 10a19 erg sa1 cma2 arcseca2) gaseous bridge between two subgroups of galaxies. The presence of absorption features in the spectrum of a background galaxy located at an impact parameter of 19 kpc from the closest galaxy of the group indicates the presence of gas enriched in magnesium even beyond the detected nebula seen in emission, which suggests that we are observing the tip of a larger intragroup medium. The observed Mg ̄II velocity gradient suggests an overall rotation of the structure along the major axis of the most massive galaxy. Our MUSE data also reveal extended Fe ̄II∗ emission in the vicinity of the most massive galaxy, aligned with its minor axis and pointing towards a neighboring galaxy. Extended [O ̄II] emission is found around the galaxy group members and at the location of the Mg ̄II bridge. Our results suggest that both tidal stripping effects from galaxy interactions and outflows are enriching the intragroup medium of this system.