Quantifying the Fragility of Galactic Disks in Minor Mergers

Abstract

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 begins with a satellite in a prograde, circular orbit inclined 30^deg^ with respect to the disk plane at a galactocentric distance of 6 disk scale lengths. The satellite's mass is 10% of the disk's mass, and its half- mass radius is ~1.3 kpc. The system is modeled with 500,000 particles, which is sufficient to mitigate numerical relaxation noise over the merging time. The satellite sinks in only ~1 Gyr and a core containing 45% of its initial mass reaches the center of the disk. With so much of the satellite's mass remaining intact, the disk sustains significant damage as the satellite passes through. At the solar circle we find that the disk thickens 60%, the velocity dispersions increase by {DELTA}σ ~ (10,8,8) km s^-1^ to (σ_R_, σphi_, σ_z_) ~ (48,42,38) km s^-1^, and the asymmetric drift is unchanged at ~18 km s^-1^. Although the disk is not destroyed by these events (hence "minor" mergers), its final state resembles a disk galaxy of an earlier Hubble type than its initial state-thicker and hotter, with the satellite's core enhancing the bulge. Thus minor mergers continue to be a promising mechanism for driving galaxy evolution.