Mergers and Galaxy Evolution (Sept94 Ringberg Workshop)

Galaxy merging is the late time manifestation of the galaxy formation process and likely significantly effects $z<1$ galaxies. A ``maximum reasonable rate'' model for merging finds a $\sim2$ mag K band increase in the luminosities of dwarf galaxies so that they contribute significantly to the faint counts, with spirals and ellipticals being far less affected. The median $K$ and $I$ redshifts stabilize (and even decrease slightly) at $z\simeq0.6$ beyond I=21 or K=19. The B redshifts continue to rise (although strongly dependent on the UV spectral evolution). Such rapid merging predicts that at $z=1$ the characteristic galaxy mass is reduced to $\sim30\%$ of the $z=0$ value. To rule out this model requires good sampling beyond $z=1$. A theoretical complication for even a minimal merger rate, which reduces $z=1$ masses to 2/3 of current epoch values, is that infall of a single satellite having 10\% of a disk's mass may destroy thin disks. Using completely self-consistent n-body simulations, we show that the primary response of a disk to ``cosmological'' satellites up to 20\% of the disk mass is to {\em tilt} the disk with a temporary warping.