Some implications of nonluminous matter in dwarf spheroidal galaxies

Abstract

Strong constraints are placed on the nature of nonluminous matter if it dominates the gravitational potential of dwarf spheroidal galaxies. In particular, the phase-space constraint in small galaxies sets a lower limit of several hundred eV on particle mass if the dark matter consists of noninteracting fermions. This limit is sufficiently strong to rule out neutrinos. Difficulties of a fundamental nature are also encountered even with more massive noninteracting particles. In scenarios where black holes comprise the nonluminous matter, they have to be less massive than approximately 100 solar masses. The quasi-exponential light profiles and dark matter in dwarf spheroidal galaxies may indicate a possible evolutionary link to dwarf irregular galaxies. Evidence is presented which supports the view that dwarf spheroidal galaxies are former dwarf irregular galaxies which lost their gas near the Milky Way via ram pressure sweeping.