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

¹ Observatoire de Genève, Universite de Genève, Chemin Pegasi 51, 1290 Versoix, Switzerland
e-mail: floriane.leclercq@unige.ch
² Aix Marseille Univ., CNRS, CNES, LAM, Marseille, France
³ Department of Physics, ETH Zürich, Wolfgang-Pauli-Strasse 27, 8093 Zürich, Switzerland
⁴ Univ. Lyon, Univ. Lyon1, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, 69230 Saint-Genis-Laval, France
⁵ Institute for Computational Astrophysics and Department of Astronomy & Physics, Saint Mary’s University, 923 Robie Street, Halifax, Nova Scotia B3H 3C3, Canada
⁶ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
⁷ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁸ Leiden Observatory, Leiden University, PO Box 9513 2300 RA Leiden, The Netherlands
⁹ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
¹⁰ Dipartimento di Fisica G. Occhialini, Università degli Studi di Milano Bicocca, Piazza della Scienza 3, 20126 Milano, Italy
¹¹ Institut de Recherche en Astrophysique et Planétologie (IRAP), Université de Toulouse, CNRS, UPS, CNES, 31400 Toulouse, France
¹² IUCAA, Post Bag 04, Ganeshkhind, Pune 411007, India
¹³ Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, VIC 3122, Australia

Received: 8 September 2021
Accepted: 20 April 2022

Abstract

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 2σ 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 z = 1.31. The galaxy group members are separated by less than 50 physical kpc in projection and ≈120 km s⁻¹ in velocity space. The most massive galaxy has a stellar mass of 10^9.35 M_⊙ 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 s⁻¹ 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 × 10⁻¹⁹ erg s⁻¹ 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, 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.