Gas condensation in brightest group galaxies unveiled with MUSE

Morphology and kinematics of the ionized gas

¹ LERMA, Observatoire de Paris, PSL Research Univ., CNRS, Sorbonne Univ., 75014 Paris, France
e-mail: valeria.olivares@obspm.fr
² Department of Physics and Astronomy, University of Kentucky, 505 Rose Street, Lexington, KY 40506, USA
³ Department of Physics, University of Bath, Claverton Down BA2 7AY, UK
⁴ Collège de France, 11 Place Marcelin Berthelot, 75005 Paris, France
⁵ INAF, Osservatorio di Astrofisica e Scienza dello Spazio, Via P. Gobetti 93/3, 40129 Bologna, Italy
⁶ Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
⁷ Centre for Space Research, North-West University, Potchefstroom 2520, South Africa
⁸ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
⁹ Sorbonne Université, CNRS, UMR 7095, Institut d’Astrophysique de Paris, 98bis bd Arago, 75014 Paris, France
¹⁰ Institute of Astronomy and Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
¹¹ Department of Physics and Astronomy, University of Victoria, Victoria, BC V8W 2Y2, Canada
¹² SOFIA Science Center, USRA, NASA Ames Research Center, M.S. N232-12, Moffett Field, CA 94035, USA
¹³ Université Lyon 1, ENS de Lyon, CNRS UMR5574, Centre de Recherche Astrophysique de Lyon, 69230 Saint-Genis-Laval, France
¹⁴ Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824, USA
¹⁵ European Southern Observatory, Alonso de Cóordova 3107, Vitacura, Casilla, 19001 Santiago de Chile, Chile
¹⁶ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
¹⁷ Université Paris-Saclay, CNRS, Institut d’Astrophysique Spatiale, 91405 Orsay, France
¹⁸ École normale supérieure, Université PSL, Sorbonne Université, CNRS, LERMA, 75005 Paris, France
¹⁹ Department of Physics and Astronomy, University of Waterloo, Waterloo, ON N2L 3G1, Canada

Received: 18 October 2021
Accepted: 18 May 2022

Abstract

The origin of the cold gas in central galaxies in groups is still a matter of debate. We present Multi-Unit Spectroscopic Explorer (MUSE) observations of 18 optically selected local (z ≤ 0.017) brightest group galaxies (BGGs) to study the kinematics and distribution of the optical emission-line gas. MUSE observations reveal a distribution of gas morphologies including ten complex networks of filaments extending up to ∼10 kpc to two compact (< 3 kpc) and five extended (> 5 kpc) disk-dominated structures. Some rotating disks show rings and elongated structures arising from the central disk. The kinematics of the stellar component is mainly rotation-dominated, which is very different from the disturbed kinematics and distribution found in the filamentary sources. The ionized gas is kinematically decoupled from the stellar component for most systems, suggesting an external origin for the gas. We also find that the Hα luminosity correlates with the cold molecular gas mass. By exploring the thermodynamical properties of the X-ray atmospheres, we find that the filamentary structures and compact disks are found in systems with small central entropy values, K, and t_cool/t_eddy ratios. This suggests that, similar to brightest cluster galaxies (BCGs) in cool core clusters, the ionized filaments and the cold gas associated to them are likely formed from hot halo gas condensations via thermal instabilities, which is consistent with the chaotic cold accretion simulations (as shown via the C ratio, Ta_t, and k plot). We note that the presence of gaseous rotating disks is more frequent than in BCGs. An explanation for the origin of the gas in those objects is a contribution to gas fueling by wet mergers or group satellites, as qualitatively hinted at by some sources of the present sample. Nonetheless, we discuss the possibility that some extended disks could also be a transition stage in an evolutionary sequence including filaments, extended disks, and compact disks, as described by hot gas condensation models of cooling flows.