Stellar Kinematics in Double-Barred Galaxies: Theσ-Hollows

Abstract

We present SAURON integral-field stellar velocity and velocity dispersion maps for four double-barred early-type galaxies: NGC 2859, NGC 3941, NGC 4725, and NGC 5850. The presence of the inner bar does not produce major changes in the line-of-sight 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 on either side of the center, at the ends of the inner bars. We have performed numerical simulations to explain these features. Ruling out other possibilities, we conclude that the σ-hollows are an effect of the contrast between two kinematically different components: the high velocity dispersion of the bulge and the more ordered motion (low velocity dispersion) of the inner bar.