|
Description
To assess how external factors such as local interactions and fresh gas accretion influence the global interstellar medium of galaxies, we analyze the relationship between recent enhancements of central star formation and total molecular-to-atomic (H_2_/HI) gas ratios, using a broad sample of field galaxies spanning early-to-late type morphologies, stellar masses of 10^7.2^-10^11.2^M_{sun}_, and diverse stages of evolution. We find that galaxies occupy several loci in a "fueling diagram" that plots H_2_/HI ratio versus mass-corrected blue-centeredness, a metric tracing the degree to which galaxies have bluer centers than the average galaxy at their stellar mass. Spiral galaxies of all stellar masses show a positive correlation between H_2_/HI ratio and mass-corrected blue-centeredness. When combined with previous results linking mass-corrected blue-centeredness to external perturbations, this correlation suggests a systematic link between local galaxy interactions and molecular gas inflow/replenishment. Intriguingly, E/S0 galaxies show a more complex picture: some follow the same correlation, some are quenched, and a distinct population of blue-sequence E/S0 galaxies (with masses below key scales associated with transitions in gas richness) defines a separate loop in the fueling diagram. This population appears to be composed of low-mass merger remnants currently in late- or post-starburst states, in which the burst first consumes the H_2_ while the galaxy center keeps getting bluer, then exhausts the H_2_, at which point the burst population reddens as it ages. Multiple lines of evidence suggest connected evolutionary sequences in the fueling diagram. In particular, tracking total gas-to-stellar mass ratios within the fueling diagram provides evidence of fresh gas accretion onto low-mass E/S0s emerging from their central starburst episodes. Drawing on a comprehensive literature search, we suggest that virtually all galaxies follow the same evolutionary patterns found in our broad sample.
|
