WALLABY pilot survey: Spatially resolved gas scaling relations within the stellar discs of nearby galaxies

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 $R_{\text{25}}$ and $R_{\text{24}}$ – 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 $R_{\text{25}}$ and 54% within $R_{\text{24}}$ , though significant variation exists between galaxies, ranging from $\sim$ 20% to 100%. The fraction of H i mass within $R_{\text{25}}$ 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 $R_{\text{24}}$ . 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 $R_{\text{25}}$ . This trend of the average H i surface density with optical colour strengthens when we restrict from $R_{\text{25}}$ to $R_{\text{24}}$ , 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.

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Journal
Publications of the Astronomical Society of Australia
Published
2025-01-01
DOI
https://doi.org/10.1017/pasa.2025.30
Citations
3
Primary Topic
Galaxies: Formation, Evolution, Phenomena
Type
article
Field-Weighted Citation Impact
3.46

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article

WALLABY pilot survey: Spatially resolved gas scaling relations within the stellar discs of nearby galaxies

Nathan Deg, T. Westmeier, J. Rhee, Seona Lee et al.
3 citations
Publications of the Astronomical Society of Australia
Galaxies: Formation, Evolution, Phenomena
3.46
article

WALLABY pilot survey: Spatially resolved gas scaling relations within the stellar discs of nearby galaxies

Nathan Deg, T. Westmeier, J. Rhee, Seona Lee, L. Cortese, Barbara Catinella, L. Staveley‐Smith, Kristine Spekkens, Benne W. Holwerda, C. Murugeshan, K. Lee-Waddell, Helga Dénes, O. Ivy Wong, Ahmed Elagali, B. Koribalski, Jing Wang
article en
3 citations

Abstract

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 $R_{\text{25}}$ and $R_{\text{24}}$ – 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 $R_{\text{25}}$ and 54% within $R_{\text{24}}$ , though significant variation exists between galaxies, ranging from $\sim$ 20% to 100%. The fraction of H i mass within $R_{\text{25}}$ 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 $R_{\text{24}}$ . 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 $R_{\text{25}}$ . This trend of the average H i surface density with optical colour strengthens when we restrict from $R_{\text{25}}$ to $R_{\text{24}}$ , 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.

Publications of the Astronomical Society of AustraliaVol. 42
Commonwealth Scientific and Industrial Research Organisation (AU), Australia Telescope National Facility (AU), University of Louisville (US), The University of Western Australia (AU), Peking University (CN), Queen's University (CA), Curtin University (AU), Universidad Yachay Tech (EC), ASTRO-3D (AU), Kavli Institute for Theoretical Sciences (CN), ARC Centre of Excellence for All-sky Astrophysics (AU), Western Australian Marine Science Institution (AU), International Centre for Radio Astronomy Research (AU), Western Sydney University (AU)
National Science Foundation, U.S. Department of Energy, National Aeronautics and Space Administration, University of Pennsylvania, Ohio State University, California Institute of Technology, University of Portsmouth, University of Sussex, Commonwealth Scientific and Industrial Research Organisation, Chinese Academy of Sciences, Ludwig-Maximilians-Universität München, Office of Science, Jet Propulsion Laboratory, Division of Astronomical Sciences, High Energy Physics, Integrated Electronics Engineering Center, Binghamton University, Lawrence Berkeley National Laboratory, SLAC National Accelerator Laboratory
Openalex Percentile: Top 8%
Galaxies: Formation, Evolution, Phenomena
3.46
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