Kinematics of Extremely Faint Dwarf Galaxies

We present the results of deep, high velocity resolution (~1.6 km/s) Giant Meterwave Radio Telescope (GMRT) HI 21cm observations of extremely faint (M_B > -12.5) dwarf irregular galaxies. We find that all of our sample galaxies show systematic large scale velocity gradients, unlike earlier studies which found chaotic velocity fields for such faint galaxies. For some of the sample galaxies the velocity fields are completely consistent with ordered rotation, though the peak circular velocities are comparable to the observed random motions. These are the faintest known galaxies with such regular kinematics. We present ("asymmetric drift" corrected) rotation curves and mass models (including fits for Isothermal and NFW halos) for some of these galaxies and discuss the implications for hierarchical models of galaxy formation.