BreakBRD Galaxies: Evolutionary Clues through an Analysis of Gas Content

Abstract By combining newly obtained deep Green Bank Telescope 21 cm observations with optical spectroscopic data, we present an analysis of the gas content of break bulges in red disks (breakBRD) galaxies, a population denoted by their blue star-forming centers and red quenched disks that do not appear to follow the typical inside-out evolution of spiral galaxies. We confirm previous results that the neutral atomic hydrogen (H i ) gas fractions of breakBRDs are, on average, lower than those of typical galaxies on the star-forming sequence (SFS), and find that their H i fractions are generally higher than green valley (GV) galaxies. H i depletion times for breakBRDs are roughly an order of magnitude lower than those of SFS galaxies, in stark contrast with GV galaxies that typically have much longer depletion times than SFS galaxies. The nuclear gas-phase metallicities of breakBRDs have a broader distribution than SFS galaxies and are skewed toward slightly above-average values. BreakBRDs are systematically offset from the baryonic Tully–Fisher relation toward lower baryonic mass at a given rotation velocity. They also have higher typical H i asymmetries than SFS galaxies, and of those galaxies with spatially resolved gas velocity fields from the Sloan Digital Sky Survey IV Mapping Nearby Galaxies at Apache Point Observatory survey, two-thirds are either highly distorted or completely misaligned relative to the stellar disk. Evidence supports a scenario where breakBRDs are in an early phase of quenching, and there is mixed evidence that their behavior is related to past merger activity.