Tracing Quenching in Nearby Galaxies through Inner Surface Mass Density and Cold Gas Content

Abstract The inner stellar mass surface density within 1 kpc, Σ 1 , has emerged as a suitable proxy for bulge growth and galaxy quenching. However, the dependence of cold gas content on Σ 1 has not been thoroughly explored. In this paper, we examine the relationship between Σ 1 , as well as the mass-relative parameter ΔΣ 1 , and the atomic ( f HI ) and molecular ( f H2 ) cold gas fractions in massive, nearby galaxies. We utilize a sample of 341 galaxies with H i data and 201 galaxies with H 2 data from the xGASS and xCOLDGASS surveys, spanning 0.02 ≤ z ≤ 0.05 and a stellar mass range of 10 10 ≤ M * / M ⊙ ≤ 10 11.5 . While we observe that a decline in both f HI and f H2 is associated with increasing Σ 1 , we find that f H2 shows a sharper decline above a threshold value of ΔΣ 1 = 0. In addition, the fraction of galaxies with active galactic nucleus (AGN) activity (Seyferts and LINERs) increases with ΔΣ 1 , with the greatest increase occurring between 0 ≲ ΔΣ 1 ≲ 0.2 dex. We propose an evolutionary track in the plane of f H2 − ΔΣ 1 , whereby molecular gas depletion at fixed mass coincides with a rise in AGN activity. Our results suggest that central bulge growth is more tightly coupled to the depletion of molecular gas rather than atomic gas, with AGN feedback possibly contributing to this process. Our work highlights the utility of Σ 1 and ΔΣ 1 as tracers of quenching in massive galaxies.