We investigate the gas content and baryonic Tully-Fisher relationship for extremely low luminosity dwarf galaxies in the absolute magnitude range -13.5 > M _ { r } -5 \log _ { 10 } h _ { 70 } > -16 .
The sample is selected from the Sloan Digital Sky Survey and consists of 101 galaxies for which we have obtained follow-up HI observations using the Arecibo Observatory and Green Bank Telescope .
This represents the largest homogeneous sample of dwarf galaxies at low luminosities with well-measured HI and optical properties .
The sample spans a range of environments , from dense groups to truly isolated galaxies .
The average neutral gas fraction is \langle f _ { gas } \rangle = 0.6 , significantly exceeding that of typical gas-rich galaxies at higher luminosities .
Dwarf galaxies are therefore less efficient at turning gas into stars over their lifetimes .
The strong environmental dependence of the gas fraction distribution demonstrates that while internal processes can reduce the gas fractions to roughly f _ { gas } = 0.4 , external processes are required to fully remove gas from a dwarf galaxy .
The average rotational velocity of our sample is \langle v _ { rot } \rangle = \langle W 20 _ { i,t } / 2 \rangle = 50 km s ^ { -1 } based on HI line-widths .
In this luminosity range , the optical Tully-Fisher relationship has significantly more scatter compared to the baryonic relationship .
Including more massive galaxies from the literature , we fit a baryonic Tully-Fisher slope of M _ { baryon } \propto v _ { rot } ^ { 3.70 \pm 0.15 } .
This slope compares well with CDM models that assume an equal baryon to dark matter ratio at all masses .
While gas stripping or other processes may modify the baryon to dark matter ratio for dwarfs in the densest environments , the majority of dwarf galaxies in our sample have not preferentially lost significant baryonic mass relative to more massive galaxies .