WALLABY: an untargeted search for H I-bearing ultra-diffuse galaxies uncovers the first known ultra-diffuse galaxy pair
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2025
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| author | O'Beirne, T. Kilborn, V. A. Cluver, M. E. Wong, O. I. Deg, N. Spekkens, K. Arora, N. Dudley, R. Catinella, B. Dénes, H. Lee-Waddell, K. Piña, P. E. Mancera Murugeshan, C. Rhee, J. Staveley-Smith, L. Shen, A. X. Westmeier, T. |
| author_facet | O'Beirne, T. Kilborn, V. A. Cluver, M. E. Wong, O. I. Deg, N. Spekkens, K. Arora, N. Dudley, R. Catinella, B. Dénes, H. Lee-Waddell, K. Piña, P. E. Mancera Murugeshan, C. Rhee, J. Staveley-Smith, L. Shen, A. X. Westmeier, T. |
| contents | 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 $μ_{g,0}\ge24$ mag arcsec$^{-2}$ and $R_{e}\ge1.5$ kpc, and a broader sample including 12 additional faint diffuse galaxies ($μ_{g,0}\ge23.7$ mag arcsec$^{-2}$ and $R_{e}\ge1.3$ kpc). Within the core sample, we highlight the first discovery of a UDG pair. 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, $\log_{10}(M_{HI}/\rm M_{\odot}) = 8.95\pm0.03$, compared to the South-Eastern UDG (WALLABY J104513-262755-UDG-2), $\log_{10}(M_{HI}/\rm M_{\odot}) = 8.60\pm0.04$. UDG-1's stellar mass and star formation rate are also approximately an order of magnitude larger at $\log_{10}(M_*/\rm M_{\odot}) = 8.07\pm0.12$ and $\log_{10}(SFR/\rm M_{\odot}~yr^{-1}) = -1.26\pm0.12$ respectively. The pair has an isolated local environment, with no other galaxies or H I sources within 30 arcmin (525 kpc) and $\pm1000$ 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. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2510_19466 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | WALLABY: an untargeted search for H I-bearing ultra-diffuse galaxies uncovers the first known ultra-diffuse galaxy pair O'Beirne, T. Kilborn, V. A. Cluver, M. E. Wong, O. I. Deg, N. Spekkens, K. Arora, N. Dudley, R. Catinella, B. Dénes, H. Lee-Waddell, K. Piña, P. E. Mancera Murugeshan, C. Rhee, J. Staveley-Smith, L. Shen, A. X. Westmeier, T. Astrophysics of Galaxies 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 $μ_{g,0}\ge24$ mag arcsec$^{-2}$ and $R_{e}\ge1.5$ kpc, and a broader sample including 12 additional faint diffuse galaxies ($μ_{g,0}\ge23.7$ mag arcsec$^{-2}$ and $R_{e}\ge1.3$ kpc). Within the core sample, we highlight the first discovery of a UDG pair. 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, $\log_{10}(M_{HI}/\rm M_{\odot}) = 8.95\pm0.03$, compared to the South-Eastern UDG (WALLABY J104513-262755-UDG-2), $\log_{10}(M_{HI}/\rm M_{\odot}) = 8.60\pm0.04$. UDG-1's stellar mass and star formation rate are also approximately an order of magnitude larger at $\log_{10}(M_*/\rm M_{\odot}) = 8.07\pm0.12$ and $\log_{10}(SFR/\rm M_{\odot}~yr^{-1}) = -1.26\pm0.12$ respectively. The pair has an isolated local environment, with no other galaxies or H I sources within 30 arcmin (525 kpc) and $\pm1000$ 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. |
| title | WALLABY: an untargeted search for H I-bearing ultra-diffuse galaxies uncovers the first known ultra-diffuse galaxy pair |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2510.19466 |