BreakBRD Galaxies: Evolutionary Clues Through an Analysis of Gas Content

TL;DR

This study analyzes the gas content of BreakBRD galaxies, revealing their unique properties such as low HI fractions, rapid depletion times, and disturbed gas kinematics, suggesting they are in an early quenching phase possibly linked to mergers.

Contribution

It provides the first comprehensive analysis combining deep HI observations and optical data to characterize the gas properties and evolutionary state of BreakBRD galaxies.

Findings

BreakBRDs have lower HI gas fractions than typical star-forming galaxies.

HI depletion times in BreakBRDs are about ten times shorter than in SFS galaxies.

Most BreakBRDs show disturbed or misaligned gas velocity fields.

Abstract

By combining newly obtained deep GBT 21cm observations with optical spectroscopic data, we present an analysis of the gas content of 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 (HI) gas fractions of BreakBRDs are on-average lower than those of typical galaxies on the star-forming sequence (SFS), and find that their \ion{H}{1} fractions are generally higher than Green Valley (GV) galaxies. HI 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 towards slightly above-average values. BreakBRDs are systematically offset from the Baryonic Tully-Fisher Relation towards lower baryonic mass at a given rotation velocity. They also have higher typical HI asymmetries than SFS galaxies, and of those galaxies with spatially resolved gas velocity fields from the SDSS-IV MaNGA 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.