Neutral hydrogen ( H i ) observations towards the Boötes dwarf spheroidal ( dSph ) galaxy ( hereafter Boötes ) , a very low luminosity metal-poor Galactic satellite , were obtained using the Parkes Radio Telescope .
We do not detect any H i in or around Boötes to a 3 \sigma upper limit of 180 ~ { } { \mathrm { M } _ { \sun } } within the optical half light radius and 8000 ~ { } { \mathrm { M } _ { \sun } } within 1.6 kpc .
Its H i mass-to-light ratio is less than 0.002 ~ { } { \mathrm { M } _ { \sun } } / L _ { \sun } , making Boötes one of the most gas-poor galaxies known .
Either reionisation severely inhibited gas infall onto the proto-Boötes , or large amounts of gas have been removed by ram pressure and/or tidal stripping .
Since Boötes lies on the mass-metallicity fundamental line , this relation and the inefficiency of star formation at the faintest end of the galaxy luminosity function must be partly driven , or at least not disrupted , by extreme gas loss in such low luminosity galaxies .
We also do not detect any H i associated with the leading tidal tail of the Sagittarius dSph galaxy , which fortuitously passes through the observed field , to a 3 \sigma column density limit of 2 \times 10 ^ { 17 } ~ { } \mathrm { cm ^ { -2 } } .
This suggests that either the leading gaseous tail is ionised , or the gas in the trailing tail was removed before the current tidal disruption of the parent dSph began .