The Baryonic Tully–Fisher Relation in the Local Group and the Equivalent Circular Velocity of Pressure-supported Dwarfs

Abstract

We explore the baryonic Tully-Fisher relation in the Local Group. Rotationally-supported Local Group galaxies adhere precisely to the relation defined by more distant galaxies. For pressure-supported dwarf galaxies, we determine the scaling factor beta (c) that relates their observed velocity dispersion to the equivalent circular velocity of rotationally-supported galaxies of the same mass such that V-o = beta(c) sigma(*). For a typical mass-to-light ratio gamma(*) = 2 M-circle dot;/L-circle dot in the V band, we find that beta(c) = 2. More generally, log beta(c)=0.25log gamma*+0.226. This provides a common kinematic scale relating pressure and rotationally-supported dwarf galaxies.