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 × 10⁵ and 2.1 × 10 ⁷ M_⊙ and 0.04M_⊙ L _⊙,B^-1 < M_HI/L_B < 1.81 M_⊙ L^-1_⊙,B The other 13 have upper limits between M_HI = 5 × 10⁵ and 4 × 10 ⁶ M_⊙ (M_{H I} /L_B < 0.24 M _⊙ L_⊙,B^-1). 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} > 10⁷ or M_{H I} < 10⁶ M_⊙. 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} < 10⁷ M_⊙ have been stripped of their gas. The required intergalactic medium density to achieve this is ̃10^-3 cm^-3.