A MUSE Study of Stellar and Ionized-Gas Kinematics in Central Group Galaxies

Understanding gas accretion and feedback in low-mass galaxy groups bridges the gap between isolated ellipticals and cluster-dominant galaxies. We present new Multi Unit Spectroscopic Explorer (MUSE) observations of 17 nearby brightest group galaxies (BGGs), revealing diverse origins for their gas reservoirs. Warm ionized gas, traced by Halpha and [N II], is detected in 77% (13/17) of the sample, with morphologies including rotating disks with or without tails and diffuse emission, rings, and filaments. Unlike brightest cluster galaxies, most BGGs host regularly rotating stars, whereas their gas displays diverse kinematics. Nearly half of the rotating gas disks are aligned with the stars, consistent with internal recycling. However, tails, diffuse emission, or rings in three aligned systems may retain signatures of past accretion or interactions. The remaining disks, ring-like structures, and most filamentary systems are misaligned, supporting gas acquisition through mergers, interactions, or halo cooling. Compact disks are consistent with centrally concentrated, low-angular-momentum gas, possibly linked to residual cooling. Most filamentary systems lie near the precipitation threshold (tcool/teddy 1-2) and preferentially occupy the turbulence-dominated region of the k-plot, supporting condensation consistent with chaotic cold accretion. All galaxies with detected X-ray halos, including those without warm gas, exhibit low central entropies (<30 keV cm 2) and short central cooling times (<3 Gyr). These conditions alone cannot predict multiphase gas, suggesting that AGN- or interaction-driven perturbations and turbulence-induced thermal instabilities help regulate condensation. No single mechanism dominates: BGGs are transitional systems in which internal recycling, environmental accretion, and cooling-driven condensation coexist, linking isolated ellipticals to cluster-dominant galaxies.