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 64 m Parkes Radio Telescope and the Australia Telescope Compact Array. Five dwarfs have H I masses between M-H (I) = 4 x 10(5) and 2.1 x 10(7) M-circle dot and 0.04 M-circle dot L-circle dot(-1),B < M-H (I)/L-B < 1.81 M-circle dot L-circle dot(-1),(B). The other 13 have upper limits between M-H (I) = 5 x 10(5) and 4 x 10(6) M-circle dot (M-H (I)/L-B < 0.24 M-circle dot L-circle dot(-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, which 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 among Sculptor group dwarfs. All objects fainter than M-B = -13 have either M-H (I) > 10(7) or M-H (I) < 10(6) M-circle dot. This gap may be explained by the ram pressure stripping mechanism at work in this dense environment in which all galaxies with M-H (I) < 10(7) M-circle dot have been stripped of their gas. The required intergalactic medium density to achieve this is similar to 10(-3) cm(-3).