The MUSE Extremely Deep Field: a first panoramic view of an Mg II
  emitting intragroup medium
  Using the exquisite MUSE eXtremely Deep Field data, we report the discovery
of an MgII emission nebula with an area above a 2$\sigma$ significance level of
1000 proper kpc$^2$, providing 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 z=1.31. The galaxy group members are separated by less
than 50 physical kpc in projection and $\approx$120 km/s in velocity space. The
most massive galaxy has a stellar mass of 10$^{9.35}$ M$_\odot$ and shows an
MgII P-Cygni line profile indicating the presence of an outflow, which is
consistent with the spatially resolved spectral analysis showing $\approx+$120
km/s shift of the MgII emission lines with respect to the systemic redshift.
The other galaxies are less massive and only show MgII in emission. The
detected MgII nebula has a maximal projected extent of $\approx$70 kpc
including a low surface brightness (2 $\times$ 10$^{-19}$
erg/s/cm$^{2}$/arcsec$^{2}$) 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, suggesting that we are observing the tip of a larger
intragroup medium. The observed MgII 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. Extended [OII] emission is found
around the galaxy group members and at the location of the MgII bridge. Our
results suggest that both tidal stripping effects from galaxy interactions and
outflows are enriching the intragroup medium of this system.
