The H IX galaxy survey IV: What does the molecular gas reveal in H i eXtreme galaxies?

Abstract Galaxies with extreme amounts of neutral atomic hydrogen (H i), known as H i-eXtreme (H ix) galaxies, paradoxically exhibit normal or low star formation rates. To investigate the bottleneck in their star formation, we present ALMA CO(1-0) observations for five H ix survey galaxies: ESO208-G026, ESO378-G003, ESO381-G005, ESO417-G018, and ESO055-G013. While these systems possess massive, extended H i discs, their molecular gas discs are compact with normal H2 masses relative to their stellar mass. Dynamical modelling with 3DBarolo reveals that the H i and molecular gas are kinematically consistent. Both gas phases show high velocity dispersions, indicating enhanced turbulence compared to regular late-type galaxies. We calculate the specific angular momentum for the stellar, atomic, and molecular components alongside the global stability parameter (q). Most of the system angular momentum is stored in the H i discs, rendering them globally stable against collapse. This stability suppresses the atomic-to-molecular gas conversion, as evidenced by extremely long H i depletion times contrasted with typical H2 depletion times. The high angular momentum and H i excess likely originate from past gas accretion or recent tidal interactions; this is especially apparent in ESO378-G003 and ESO381-G005, which exhibit extended H i structures and positive tidal indices.

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Publication Details

Journal
Monthly Notices of the Royal Astronomical Society
Published
2026-10-28
DOI
https://doi.org/10.1093/mnras/stag2057
Primary Topic
Galaxies: Formation, Evolution, Phenomena
Type
article
Field-Weighted Citation Impact
0.00

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article

The H IX galaxy survey IV: What does the molecular gas reveal in H i eXtreme galaxies?

Katharina Lutz, H Dénes, V A Capa, T H Brown
1 links
Monthly Notices of the Royal Astronomical Society
Galaxies: Formation, Evolution, Phenomena
article

The H IX galaxy survey IV: What does the molecular gas reveal in H i eXtreme galaxies?

Katharina Lutz, H Dénes, V A Capa, T H Brown
article en

Abstract

Abstract Galaxies with extreme amounts of neutral atomic hydrogen (H i), known as H i-eXtreme (H ix) galaxies, paradoxically exhibit normal or low star formation rates. To investigate the bottleneck in their star formation, we present ALMA CO(1-0) observations for five H ix survey galaxies: ESO208-G026, ESO378-G003, ESO381-G005, ESO417-G018, and ESO055-G013. While these systems possess massive, extended H i discs, their molecular gas discs are compact with normal H2 masses relative to their stellar mass. Dynamical modelling with 3DBarolo reveals that the H i and molecular gas are kinematically consistent. Both gas phases show high velocity dispersions, indicating enhanced turbulence compared to regular late-type galaxies. We calculate the specific angular momentum for the stellar, atomic, and molecular components alongside the global stability parameter (q). Most of the system angular momentum is stored in the H i discs, rendering them globally stable against collapse. This stability suppresses the atomic-to-molecular gas conversion, as evidenced by extremely long H i depletion times contrasted with typical H2 depletion times. The high angular momentum and H i excess likely originate from past gas accretion or recent tidal interactions; this is especially apparent in ESO378-G003 and ESO381-G005, which exhibit extended H i structures and positive tidal indices.

Monthly Notices of the Royal Astronomical Society
Herzberg Institute of Astrophysics (CA), University of Victoria (CA), Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR) (DE), Universidad Yachay Tech (EC), National Research Council Canada (CA), Universidad San Francisco de Quito (EC)
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 Chicago, University of Portsmouth, National Radio Astronomy Observatory, Australian Government, University College London, University of Sussex, Commonwealth Scientific and Industrial Research Organisation, Deutsche Forschungsgemeinschaft, Chinese Academy of Sciences, Korea Astronomy and Space Science Institute, Financiadora de Estudos e Projetos, National Astronomical Observatory of Japan, University of Illinois at Urbana-Champaign, Office of Science, Jet Propulsion Laboratory, Science and Technology Facilities Council, National Institutes of Natural Sciences, Division of Astronomical Sciences, High Energy Physics, Integrated Electronics Engineering Center, Binghamton University, Argonne National Laboratory, Fermilab, Lawrence Berkeley National Laboratory, SLAC National Accelerator Laboratory
Openalex Percentile: Top 14%
Galaxies: Formation, Evolution, Phenomena
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