Dark Matter in Dwarf Galaxies

Abstract

This paper reviews the observational evidence for dark matter (DM) in dwarf spiral (dS) and dwarf spheroidal (dE) galaxies. The most secure detection of DM in dwarf galaxies is given by HI rotation curves. They provide estimates of DM halo parameters, i. e., isothermal core radii r c , central densities ρ 0 and one-dimensional velocity dispersions σ. The smallest DM halo measured so far is in DDO 127 ( M B = −14.5 for H 0 = 75 km s −1 Mpc −1 , r c ≃ 2.3 kpc, σ ≃ 27 km s −1 ). If this halo is made of neutrinos of mass m v , then phase-space constraints imply that m v > 110 eV. This is difficult to reconcile with cosmological upper limits giving Ω ≤ 1. Ultimately, dE galaxies will provide the strongest constraints on DM in dwarf galaxies; a detailed look at present results shows that they are not yet conclusive.