The galaxy velocity function for extremely low mass galaxies

The number of observed low mass galaxies is in conflict with the number predicted by standard cosmological models. Rotation velocities of galaxies provide the observational link to compare the number density of galaxies with a dark matter halo (velocity function). We have used highly sensitive observations of extremely low mass galaxies to populate the unconstrained low mass end of the velocity function of galaxies and compare these observations with simulations of dark matter halos.