Lifetime of nuclear velocity dispersion drops in barred galaxies

We have made hydro/N-body simulations with and without star formation to shed some light on the conditions under which a central kinematically cold stellar component (characterized by a velocity dispersion drop or sigma-drop) could be created in a hot medium (e.g. a bulge) and survive enough time to be observed. We found that the time-scale for a sigma-drop formation could be short (less than 500 Myr), whereas its lifetime could be long (more than 1 Gyr) provided that the central region is continuously or regularly fed by fresh gas which leads to a continuous star formation activity. Star formation in the central region, even at a low rate as 1 M(circle dot) yr(-1), is mandatory to sustain a permanent sigma-drop by replacing heated particles by new low-sigma ones. We moreover show that as soon as star formation is switched off, the sigma-drop begins to disappear.