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 M _ { HI } = 4 \times 10 ^ { 5 } to M _ { HI } = 2.1 \times 10 ^ { 7 } M _ { \odot } and 0.04 < M _ { HI } / L _ { B } < 1.81 M _ { \odot } L _ { \odot, { B } } ^ { -1 } .
The other 13 have upper-limits between M _ { HI } < 5 \times 10 ^ { 5 } and M _ { HI } < 4 \times 10 ^ { 6 } M _ { \odot } ( M _ { HI } / L _ { B } < 0.24 M _ { \odot } L _ { \odot, { 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 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 M _ { B } = -13 have either M _ { HI } > 10 ^ { 7 } M _ { \odot } or M _ { HI } < 10 ^ { 6 } M _ { \odot } .
This gap may be explained by the ram pressure stripping mechanism at work in this dense environment where all galaxies with M _ { HI } < 10 ^ { 7 } M _ { \odot } have been stripped of their gas .
The required intergalactic medium density to achieve this is \sim 10 ^ { -3 } cm ^ { -3 } .