Kinematics of Inner Bars. The Stellar σ-Hollows

Abstract

We present SAURON stellar kinematical analysis for four double-barred early-type galaxies: NGC 2859, NGC 3941, NGC 4725 and NGC 5850. The presence of the inner bar is not evident from the radial velocity, but it appears to have an important effect in the stellar velocity dispersion maps: we find two σ-hollows of amplitudes between 10 and 40 km s− 1 at either sides of the center, at the ends of the inner bars. We have performed numerical simulations to explain these features. Ruling out other possibilities, we finally conclude that, although the σ-hollows might be originated by a younger stellar population component with low velocity dispersion. More likely they are an effect of the contrast between two kinematically different components: the bulge, with its high velocity dispersion, and the inner bar, characterized by its low velocity dispersion (ordered motion).