ar X iv : a st ro - p h / 06 11 42 3 v 1 1 4 N ov 2 00 6 Interstellar medium disruption in the Centaurus A group

We present the results of a 21 cm neutral hydrogen (H i) line detection experiment in the direction of 18 low luminosity dwarf galaxies of the Centaurus A group, using the Australia Telescope National Facility 64m Parkes Radio Telescope and the Australia Telescope Compact Array. Five dwarfs have H i masses between MHI = 4 × 10 5 to MHI = 2.1 × 10 7 M⊙ and 0.04 < MHI/LB < 1.81 M⊙L −1 ⊙,B. The other 13 have upper-limits between MHI < 5 × 10 5 and MHI < 4 × 10 M⊙ (MHI/LB < 0.24 M⊙L −1 ⊙,B). Two of the mixed-morphology dwarfs remain undetected in H i, a situation that is in contrast to that of similar Local Group and Sculptor group objects where all contain significant amounts of neutral gas. There is a discontinuity in the H i properties of Centaurus A group low luminosity dwarfs that is unobserved amongst Sculptor group dwarfs. All objects fainter than MB = −13 have either MHI > 10 7 M⊙ or MHI < 10 6 M⊙. This gap may be explained by the ram pressure stripping mechanism at work in this dense environment where all galaxies with MHI < 10 7 M⊙ have been stripped of their gas. The required intergalactic medium density to achieve this is ∼ 10 cm.