Gas condensation in Brightest Group Galaxies unveiled with MUSE

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 rotationdominated, 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 find also 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, like for Brightest Cluster Galaxies (BCGs) in cool core clusters, the ionized filaments and the cold gas associated are likely formed from hot halo gas condensations via thermal instabilities, consistently 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 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.

Merger histories of brightest group galaxies from MUSE stellar kinematics

“…as illustrated by the grey bands in Figure 2. Our stellar kinematic maps and measurements agree with those from Olivares et al (2022) who used the Indo-US library (Valdes et al 2004). We limit the fit to a wavelength range of 4800 to 6800 Å, to avoid any potentially strong telluric and sky residuals.…”

“…The observations and data reduction are fully described in Lagos et al (2022a) and Olivares et al (2022), and we only summarise the most relevant information here. Our sample consists of 18 BGEs from the CLoGS sample (O'Sullivan et al 2017), presented in Table 1.…”

“…The misalignment of cold gas and ionised gas with the stellar rotation in galaxies can suggest clues to the origin of accreted gas. We therefore use the gas kinematic position angle (PA gas ) from Olivares et al (2022), and the stellar PA kin measured here, to derive the misalignment between gas and stars (Ψ gas ). Both the PA gas and PA kin were measured from North (anti-clockwise) to maximum velocity, and the difference between the two angles is defined as Ψ gas measured between 0 • (fully aligned) to 180 • (fully counter-aligned).…”

“…This paper is part of a series analysing 18 Multi-Unit Spectroscopic Explorer (MUSE; Bacon et al 2010) cubes of CLoGS BGEs. Olivares et al (2022) present a detailed analysis of the ionised gas kinematics, Lagos et al (2022a) present an analysis of gas ionisation mechanisms and chemical abundances, and here we present detailed stellar kinematics. Dynamical modelling, and stellar population analyses will be presented in future papers.…”

Baryon Cycles in the Biggest Galaxies

“…It is also tempting to infer the level of turbulence in the hot atmosphere from observations of denser multiphase gas components embedded within it. Observations show that line-of-sight speeds measured from Doppler shifts of the Hα line tracing 10 4 K gas correlate well with speeds inferred from Doppler shifts of molecular lines tracing much denser gas [509,510]. Likewise, the velocity dispersions of differing gas phases observed in idealized numerical simulations of AGN feedback exhibit similarly strong correlations [511, see Figure 35].…”