Asymmetric drift and the stellar velocity ellipsoid

Abstract

We present the decomposition of the stellar velocity ellipsoid using stellar velocity dispersions within a 40◦ wedge about the major-axis (σmaj), the epicycle approximation, and the asymmetric drift equation. Thus, we employ no fitted forms for σmaj and escape interpolation errors resulting from comparisons of the major and minor axes. We apply the theoretical construction of the method to integral field data taken for NGC 3949 and NGC 3982. We derive the vertical-to-radial velocity dispersion ratio (σz/σR) and find (1) our decomposition method is accurate and reasonable, (2) NGC 3982 appears to be rather typical of an Sb type galaxy with σz/σR = 0.73+0.13−0.11 despite its high surface brightness and small size, and (3) NGC 3949 has a hot disk with σz/σR = 1.18+0.36−0.28.