2025/01/01 by Seona Lee, Lee, Seona, Barbara Catinella +29 · 1 voice · 1 citation
Physics and Astronomy · #Galaxies: Formation, Evolution, Phenomena
paper · pdf · doi:10.1017/pasa.2025.30
openalex publication_date 2025/01/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/01
Abstract The scatter in global atomic hydrogen (H i ) scaling relations is partly attributed to differences in how H i and stellar properties are measured, with H i reservoirs typically extending beyond the inner regions of galaxies where star formation occurs. Using pilot observations from the Widefield ASKAP L-band Legacy All-sky Blind Survey (WALLABY), we present the first measurements of H i mass enclosed within the stellar-dominated regions of galaxies for a statistical sample of 995 local gas-rich systems, investigating the factors driving its variation. We examine how global H i scaling relations change when measurements are restricted to R25 and R24 – the isophotal radii at 25 and 24 mag arcsec -2 in the i -band – and explore how the fraction of H i mass and H i surface density within these radii correlate with other galaxy properties. On average, 68% of the total H i mass is enclosed within R25 and 54% within R24 , though significant variation exists between galaxies, ranging from ∼ 20% to 100%. The fraction of H i mass within R25 shows a mild correlation with stellar properties, with galaxies of higher stellar mass, greater stellar surface density, or redder colours enclosing a larger fraction of their H i reservoirs. These correlations do not significantly strengthen when considering R24 . Conversely, global H i surface densities show no significant correlation with stellar mass or stellar surface density, but trends start emerging when these are measured within the inner regions of galaxies. The strongest correlation is observed with optical colour, with bluer galaxies having higher average H i surface densities within R25 . This trend of the average H i surface density with optical colour strengthens when we restrict from R25 to R24 , suggesting a closer connection between inner H i reservoirs and star formation. This study underscores the value of (at least marginally) resolved H i surveys of statistical samples for advancing our understanding of the gas-star formation cycle in galaxies.