QUANTIFYING THE FRAGILITY OF GALACTIC DISKS IN MINOR MERGERS

We perform fully self-consistent stellar dynamical simulations of the accretion of a companion (''satellite'') galaxy by a large disk galaxy to investigate the interaction between the disk, halo, and satellite components of the system during a merger. Our fiducial encounter begin s with a satellite in a prograde, circular orbit inclined 30 degrees w ith respect to the disk plane at a galactocentric distance of 6 disk s cale lengths. The satellite's mass is 10% of the disk's mass, and its half-mass radius is similar to 1.3 kpc. The system is modeled with 500 ,000 particles, which is sufficient to mitigate numerical relaxation n oise over the merging time. The satellite sinks in only similar to 1 G yr and a core containing similar to 45% of its initial mass reaches th e center of the disk. With so much of the satellite's mass remaining i ntact, the disk sustains significant damage as the satellite passes th rough. At the solar circle we find that the disk thickens similar to 6 0%, the velocity dispersions increase by Delta sigma similar or equal to (10, 8, 8) km s(-1) to (sigma(R), sigma(phi), sigma(z)) similar or equal to (48, 42, 38) km s(-1), and the asymmetric drift is unchanged at similar to 18 km s(-1). Although the disk is not destroyed by these events (hence ''minor'' mergers), its final state resembles a disk ga laxy of an earlier Hubble type than its initial state-thicker and hott er, with the satellite's core enhancing the bulge. Thus minor mergers continue to be a promising mechanism for driving galaxy evolution.