WALLABY: an untargeted search for H  <scp>i</scp> -bearing ultra-diffuse galaxies uncovers the first known ultra-diffuse galaxy pair

ABSTRACT Using the Widefield ASKAP L-band Legacy All-sky Blind surveY (WALLABY), we performed an untargeted search for H i-bearing ultra-diffuse galaxies (UDGs). We identified a core sample of 10 UDGs defined by $\mu _{0,g}\ge 24$ mag arcsec$^{-2}$ and $R_{\rm e}\ge 1.5$ kpc, and a broader sample including 12 additional faint diffuse galaxies ($\mu _{0,g}\ge 23.7$ mag arcsec$^{-2}$ and $R_{\rm e}\ge 1.3$ kpc). Within the core sample, we highlight the first discovery of a pair of UDGs. Their projected separation is just 75 arcsec (22 kpc at 61.9 Mpc), with a central H i velocity difference of 34 km s$^{-1}$. The north-western UDG (WALLABY J104513−262755-UDG-1) has a larger H i reservoir, $\log _{10}(M_{\rm H\, {\small I}}/\rm {\rm M}_{\odot }) = 8.95\pm 0.03$, compared with the south-eastern UDG (WALLABY J104513−262755-UDG-2), $\log _{10}(M_{\rm H\, {\small I}}/\rm {\rm M}_{\odot }) = 8.60\pm 0.04$. The stellar mass and star formation rate of UDG-1 are also approximately an order of magnitude larger at $\log _{10}(M_*/\rm {\rm M}_{\odot }) = 8.07\pm 0.12$ and $\log _{10}({\rm SFR}/{\rm M}_{\odot}\,{\rm yr}^{-1}) = -1.26\pm 0.12$, respectively. The pair has an isolated local environment, with no other galaxies or H i sources within 30 arcmin (525 kpc) and $\pm 1000$ km s$^{-1}$. However, in the context of the larger-scale structure, the pair is located outside the virial radius of the Hydra cluster, with its position on the phase-space diagram indicating that it is infalling into the cluster. The identification of this H i-bearing UDG pair raises important questions around the formation of such a unique system and the evolution of UDGs in a transitional phase before ram pressure stripping and cluster infall.

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Journal
Monthly Notices of the Royal Astronomical Society
Published
2025-10-23
DOI
https://doi.org/10.1093/mnras/staf1840
Primary Topic
Astronomy and Astrophysical Research
Type
article
Field-Weighted Citation Impact
0.00

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article

WALLABY: an untargeted search for H  i -bearing ultra-diffuse galaxies uncovers the first known ultra-diffuse galaxy pair

Nathan Deg, T. Westmeier, Nikhil Arora, Jonghwan Rhee et al.
Monthly Notices of the Royal Astronomical Society
Astronomy and Astrophysical Research
article

WALLABY: an untargeted search for H  i -bearing ultra-diffuse galaxies uncovers the first known ultra-diffuse galaxy pair

Nathan Deg, T. Westmeier, Nikhil Arora, Jonghwan Rhee, V. A. Kilborn, Barbara Catinella, T. O’Beirne, Lister Staveley‐Smith, Kristine Spekkens, Ao Shen, M. E. Cluver, Pavel E. Mancera Piña, C. Murugeshan, K. Lee-Waddell, Helga Dénes, O. Ivy Wong, R. M. Dudley
article en

Abstract

ABSTRACT Using the Widefield ASKAP L-band Legacy All-sky Blind surveY (WALLABY), we performed an untargeted search for H i-bearing ultra-diffuse galaxies (UDGs). We identified a core sample of 10 UDGs defined by $\mu _{0,g}\ge 24$ mag arcsec$^{-2}$ and $R_{\rm e}\ge 1.5$ kpc, and a broader sample including 12 additional faint diffuse galaxies ($\mu _{0,g}\ge 23.7$ mag arcsec$^{-2}$ and $R_{\rm e}\ge 1.3$ kpc). Within the core sample, we highlight the first discovery of a pair of UDGs. Their projected separation is just 75 arcsec (22 kpc at 61.9 Mpc), with a central H i velocity difference of 34 km s$^{-1}$. The north-western UDG (WALLABY J104513−262755-UDG-1) has a larger H i reservoir, $\log _{10}(M_{\rm H\, {\small I}}/\rm {\rm M}_{\odot }) = 8.95\pm 0.03$, compared with the south-eastern UDG (WALLABY J104513−262755-UDG-2), $\log _{10}(M_{\rm H\, {\small I}}/\rm {\rm M}_{\odot }) = 8.60\pm 0.04$. The stellar mass and star formation rate of UDG-1 are also approximately an order of magnitude larger at $\log _{10}(M_*/\rm {\rm M}_{\odot }) = 8.07\pm 0.12$ and $\log _{10}({\rm SFR}/{\rm M}_{\odot}\,{\rm yr}^{-1}) = -1.26\pm 0.12$, respectively. The pair has an isolated local environment, with no other galaxies or H i sources within 30 arcmin (525 kpc) and $\pm 1000$ km s$^{-1}$. However, in the context of the larger-scale structure, the pair is located outside the virial radius of the Hydra cluster, with its position on the phase-space diagram indicating that it is infalling into the cluster. The identification of this H i-bearing UDG pair raises important questions around the formation of such a unique system and the evolution of UDGs in a transitional phase before ram pressure stripping and cluster infall.

Monthly Notices of the Royal Astronomical SocietyVol. 544(2)
Leiden University (NL), Commonwealth Scientific and Industrial Research Organisation (AU), Australia Telescope National Facility (AU), European Southern Observatory (DE), The University of Western Australia (AU), University of Toronto (CA), Queen's University (CA), Curtin University (AU), Universidad Yachay Tech (EC), Arthur B. McDonald-Canadian Astroparticle Physics Research Institute (CA), Astronomy and Space (AU), International Centre for Radio Astronomy Research (AU), Swinburne University of Technology (AU), Universidad San Francisco de Quito (EC)
Science and Industry Endowment Fund, Australian Government, Commonwealth Scientific and Industrial Research Organisation, Government of Western Australia
Openalex Percentile: Top 67%
Astronomy and Astrophysical Research
DOIOpen Access PDFOpenAlex
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