MIGHTEE H I observations of low surface brightness and ultra-diffuse galaxies in the XMM-LSS field

¹ ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991, PD, Dwingeloo, The Netherlands
² Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV, Groningen, The Netherlands
³ Centre for Astrophysics Research, School of Physics, Astronomy and Mathematics, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
⁴ Astrophysics, Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK
⁵ School of Physics, H.H. Wills Physics Laboratory, Tyndall Avenue, University of Bristol, Bristol BS8 1TL, UK
⁶ Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA, Leiden, The Netherlands
⁷ Sterrenkundig Observatorium, Krijgslaan 281 S9, B-9000 Gent, Belgium
⁸ STFC UK Astronomy Technology Centre, Royal Observatory, Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
⁹ Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh EH9 3HJ, UK
¹⁰ Astrophysics, Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK
¹¹ Department of Physics and Astronomy, University of the Western Cape, Robert Sobukwe Road, 7535, Bellville, Cape Town, South Africa
¹² INAF – Osservatorio Astronomico di Cagliari, Via della Scienza 5, I-09047 Selargius (CA), Italy
¹³ University of Strasbourg, CNRS UMR 7550, Observatoire astronomique de Strasbourg, F-67000 Strasbourg, France
¹⁴ SISSA International School for Advanced Studies, Via Bonomea 265, I-34136 Trieste, Italy
¹⁵ QGSKY, INFN-Sezione di Trieste, via Valerio 2, I-34127 Trieste, Italy
¹⁶ IFPU Institute for Fundamental Physics of the Universe, Via Beirut, 2, 34151 Trieste, Italy

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Received: 9 September 2025
Accepted: 16 January 2026

Abstract

Untargeted neutral hydrogen (H I) surveys are well suited to identifying low surface brightness galaxies (LSBGs) that are gas rich, and they offer a complementary view to optically selected populations. We examined the LSBG population as identified via stellar and gaseous content using the MIGHTEE H I XMM-LSS early science data and the publicly available catalogs of optically identified LSBGs. There is currently little overlap between these datasets, with only three galaxies commonly detected. We performed surface brightness photometry of selected MIGHTEE H I detections to find 29 LSBGs, and 26 of these meet the size requirement (R_eff > 1.5 kpc) to be ultra-diffuse galaxies (UDGs). Furthermore, we extracted H I spectra at the location of all optically identified galaxies, placing upper limits on the H I-to-stellar mass ratio in these systems. While the H I-identified population overall tends toward bluer colors, the H I-identified and the optically selected samples mostly overlap in mean effective surface brightness, effective radii, and color. Although it is not straightforward to discern why the H I-identified LSBGs were missed in optical searches, this work highlights the utility of H I surveys in finding these faint systems. The H I-identified LSBGs are gas rich compared to the general H I-selected population. Furthermore, three out of four H I-selected UDGs with available kinematics show no systematic offset from the baryonic Tully-Fisher relation, although we are biased away from sources with low rotational velocities due to the low spectral resolution of the data. This work demonstrates the utility of H I observations for finding and characterizing the low surface brightness Universe.