Coevolution of galactic cores and spiral galaxies

Using high-resolution N-body/smoothed particle hydrodynamics simulations with 2 x 10(6) particles, we investigate the evolution of stellar and gaseous galactic cores during the hierarchical formation of a spiral galaxy. We find that the galactic core (r < 300 pc) coevolves with the host galaxy. The average mass ratio between the baryonic core and the halo is nearly constant, ∼0.04 from z ∼10 to z ∼2. However, there are several rapid-growing phases during the evolution, in which the rate of mass accretion to the central subkiloparsec region is 10 times higher (∼1 M-. yr pc(-1)) than the average accretion rate. The rapid growth of the inner core is associated with the major merger events with a time delay. We also find that the spin axis of the gas core frequently changes. As a result, the angular momentum vector of the central part of the galaxy is independent of the rotation of the outer part. Our results suggest that if a constant fraction of the baryonic mass in the central several 100 pc of a galaxy is converted into a massive black hole, the black hole mass should correlate with the total mass of the galaxies.