2005A&A...429L...5D

Australia Telescope Compact Array multi-configuration mosaicing of the Grus quartet of galaxies reveals the presence of spectacular tidal structures. 2.1x10⁹M_☉ of neutral atomic hydrogen (HI) gas, i.e. 11% of all HI in the group, are found to be dragged from NGC 7582 into intergalactic space. About 1.34x10⁹M_☉ of HI gas are contained in a tidal tail emanating from the north-western disk of NGC 7582, with a projected length of about 85kpc and width of up to 32kpc and a relative velocity with respect to the centre of NGC 7582 of 130-140km/s. 7.7x10⁸M_☉ of HI reside in an intergalactic HI cloud 48kpc West of NGC 7582, which might originate from the disk of NGC 7582 as well and has no optical counterpart in a red Digital Sky Survey (DSS) image. These observations prove that tidal stripping is occurring in the Grus quartet and that tidal features in compact groups can be potentially important contributors of metal-enriched matter to the intergalactic medium. The tidal features around NGC 7582 cover an area of about 2000kpc², almost doubling the group's cross-section for Lyman-α absorption of light from background sources compared to the optical extent of the member galaxies.