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Published May 2025 | Version Published
Journal Article Open

A Neutral Hydrogen Absorption Study of Cold Gas in the Outskirts of the Magellanic Clouds Using the GASKAP-H i Survey

Creators

  • 1. ROR icon University of Wisconsin–Madison
  • 2. ROR icon Australian National University
  • 3. ROR icon Commonwealth Scientific and Industrial Research Organisation
  • 4. ROR icon Laboratoire de Physique de l'ENS de Lyon
  • 5. ROR icon Stanford University
  • 6. School of Physical Sciences and Nanotechnology, Yachay Tech University, Hacienda San José S/N, 100119, Urcuquí, Ecuador
  • 7. ROR icon University of Tasmania
  • 8. ROR icon Western Kentucky University
  • 9. ROR icon California Institute of Technology
  • 10. ROR icon International Centre for Radio Astronomy Research
  • 11. ROR icon University of Calgary
  • 12. ROR icon Korea Astronomy and Space Science Institute
  • 13. ROR icon Korea University of Science and Technology
  • 14. ROR icon Max Planck Institute for Radio Astronomy
  • 15. ROR icon Space Telescope Science Institute
  • 16. ROR icon Johns Hopkins University
  • 17. ROR icon Universidad de Guanajuato
  • 18. ROR icon Keele University
  • 19. ROR icon National Autonomous University of Mexico

Abstract

Cold neutral hydrogen (H i) is a crucial precursor for molecular gas formation and can be studied via H i absorption. This study investigates H i absorption in low column density regions of the Small and Large Magellanic Clouds (SMC and LMC) using the Galactic-ASKAP H i (GASKAP-H i) survey, conducted by the Australian Square Kilometer Array Pathfinder (ASKAP). We select 10 SMC directions in the outer regions and 18 LMC directions, with four in the outskirts and 14 within the main disk. Using the radiative transfer method, we decompose the emission and absorption spectra into individual cold neutral medium (CNM) and warm neutral medium (WNM) components. In the SMC, we find H i peak optical depths of 0.09–1.16, spin temperatures of ∼20–50 K, and CNM fractions of 1%–11%. In the LMC, optical depths range from 0.03–3.55, spin temperatures from ∼10–100 K, and CNM fractions from 1%–100%. The SMC's low CNM fractions likely result from its low metallicity and large LOS depth. Additionally, the SMC's outskirts show lower CNM fractions than the main body, potentially due to increased CNM evaporation influenced by the hot Magellanic Corona. Shell motions dominate the kinematics of the majority of CNM clouds in this study and likely supply cold H i to the Magellanic Stream. In the LMC, high CNM fraction clouds are found near supergiant shells, where thermal instability induced by stellar feedback promotes WNM-to-CNM transition. Although no carbon monoxide has been detected, enhanced dust shielding in these areas helps maintain the cold H i.

Copyright and License

© 2025. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Acknowledgement

We thank the anonymous referee for suggestions that improved the clarity of this paper. This scientific work uses data obtained from Inyarrimanha Ilgari Bundaran/the Murchison Radio-astronomy Observatory. We acknowledge the Wajarri Yamaji People as the Traditional Owners and native title holders of the Observatory site. CSIRO's ASKAP radio telescope is part of the Australia Telescope National Facility (https://ror.org/05qajvd42). Operation of ASKAP is funded by the Australian Government with support from the National Collaborative Research Infrastructure Strategy. ASKAP uses the resources of the Pawsey Supercomputing Research Centre. Establishment of ASKAP, Inyarrimanha Ilgari Bundara, the CSIRO Murchison Radio-astronomy Observatory and the Pawsey Supercomputing Research Centre are initiatives of the Australian Government, with support from the Government of Western Australia and the Science and Industry Endowment Fund.

This research was partially funded by the Australian Government through an Australian Research Council Australian Laureate Fellowship (project No. FL210100039) to N.Mc-.G. S.S. acknowledges the support provided by the University of Wisconsin-Madison Office of the Vice Chancellor for Research and Graduate Education with funding from the Wisconsin Alumni Research Foundation, and the NSF award AST-2108370, and NASA award 80NSSC21K0991. S.E.C. acknowledges support from NSF award AST-2106607, NASA award 80NSSC23K0972, and an Alfred P. Sloan Research Fellowship.

Data Availability

This paper includes archived data obtained through the CSIRO ASKAP Science Data Archive, CASDA at https://research.csiro.au/casda.

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Additional details

Related works

Is supplemented by
Dataset: https://research.csiro.au/casda (URL)

Funding

National Science Foundation
AST-2108370
National Aeronautics and Space Administration
80NSSC21K0991
National Science Foundation
AST-2106607
National Aeronautics and Space Administration
80NSSC23K097
Australian Research Council
Australian Laureate Fellowship FL210100039
Wisconsin Alumni Research Foundation
Alfred P. Sloan Foundation
Alfred P. Sloan Research Fellowship -

Dates

Available
2025-04-30
Published online

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Caltech groups
Owens Valley Radio Observatory, Division of Physics, Mathematics and Astronomy (PMA)
Publication Status
Published