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arXiv · 2509.17848

WALLABY Pilot Survey: the extensive interaction of NGC 4532 and DDO 137 with the Virgo cluster

L. Staveley-Smith·K. Bekki·A. Boselli·L. Cortese·N. Deg·B. -Q. For·K. Lee-Waddell·T. O'Beirne·M. E. Putman·C. Sinnott·J. Wang·T. Westmeier·O. I. Wong·B. Catinella·H. Dénes·J. Rhee·L. Shao·A. X. Shen·K. Spekkens
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Abstract

As part of the pilot survey of the Widefield ASKAP L-band Legacy All-sky Survey (WALLABY), high-resolution neutral atomic hydrogen (HI) observations of the dwarf galaxy pair NGC 4532/DDO 137 (WALLABY J123424+062511) have revealed a huge (48 kpc) bridge of gas between the two galaxies, as well as numerous arms and clouds which connect with the even longer (0.5 Mpc) tail of gas previously discovered with the Arecibo telescope. Our modelling suggests that a combination of ram pressure and tidal forces are responsible for the nature of the system. Although the pair lies well outside of the virial radius of the Virgo cluster, ram pressure due to infall through an extensive envelope of hot gas around the cluster is most likely responsible for the HI tail. Over a timescale of 1 Gyr, the predicted electron density ($1.2\times 10^{-5}$ cm$^{-3}$) and infall velocity (880 km s$^{-1}$) are probably sufficient to explain the extensive stripping from the common gaseous envelope of NGC 4532/DDO 137. The ongoing tidal interaction with the Virgo cluster appears to have prevented a rapid merger of the binary pair, with the mutual tidal interaction between the galaxy pair being responsible for raising gas from the outer parts of the galaxy potential wells into the HI bridge and common envelope. The NGC 4532/DDO 137 system mirrors many of the physical features of the Magellanic System, and may lead to a better understanding of that system, as well as casting more light on the relative importance of interaction mechanisms in the outskirts of dynamically young galaxy clusters such as Virgo.

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L. Staveley-Smith, K. Bekki, A. Boselli, L. Cortese, N. Deg, B. -Q. For, K. Lee-Waddell, T. O'Beirne, M. E. Putman, C. Sinnott, J. Wang, T. Westmeier, O. I. Wong, B. Catinella, H. Dénes, J. Rhee, L. Shao, A. X. Shen, K. Spekkens. 2025-09-22. WALLABY Pilot Survey: the extensive interaction of NGC 4532 and DDO 137 with the Virgo cluster. https://arxiv.org/abs/2509.17848

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