Numerical simulations of central stellar velocity dispersion drops in disc galaxies

We present an interpretation of the stellar velocity dispersion drops discovered in the nuclear regions of three barred galaxy hosts of active/starburst galactic nuclei (NGC 1097, NGC1808 and NGC5728) by Emsellem et al. (2001). Using self-consistent N-body simulations including stars, gas and star formation, we show that young stars born in the nuclear regions from dynamically cold gas have a lower velocity dispersion than the older stellar population. The young population (less than 0.9 Gyr old in our models), being more massive and brighter than the older one at near infrared wavelengths, fully dominates the observed line-of-sight kinematics of the circumnuclear regions.