The Relationship Between Inner Surface Mass Density and Cold Gas Content in Nearby, Star-Forming Galaxies

It is well known that the amount of cold gas in a galaxy is correlated with its star-formation rate, i.e. star-forming galaxies tend to host more gas. In addition, recent work has revealed tight correlations between star-formation rate and various structural parameters, notably the stellar surface mass density within the inner 1 kpc, Σ₁. Since cold gas is necessary for star formation, one would also expect correlations to exist between gas content and galaxy structure. To test this, we explore a number of these morphological parameters — stellar mass (M_*), global stellar mass surface density (μ_*), and Σ₁ — and their correlations with atomic (HI) and molecular (H2) hydrogen gas content. Our gas measurements are taken from the xCOLDGASS, xGASS, and ALFALFA surveys, yielding a sample of 94 galaxies with H₂ detections and 4,384 galaxies with HI detections within a redshift range of 0.02 < z < 0.05, a stellar mass range of 10¹⁰ < M_* < 10^11.5 for H₂ and 10⁸ < M_* < 10^11.5 for HI. Structural parameters were obtained from publicly available catalogs based on Sloan Digital Sky Survey observations of these objects. We identify statistically significant correlations between Σ₁ and gas content. We see similar strong correlations with Σ₁ and both depletion timescales (t_dep) and total gas fraction ( (H₂ + HI) / M_*). Our findings highlight the predictive power of Σ₁ and offer a method to estimate cold gas content within a factor of ≈ 3, using readily available parameters for large samples of galaxies.