Morphological evolution and galactic sizes in the L-Galaxies SA model.

In this work we update the L-Galaxies semi-analytic model (SAM) to better follow the physical processes responsible for the growth of bulges via disk instabilities (leading to pseudo-bulges) and mergers (leading to classical bulges), showing the impact of these processes on the fractional breakdown of our galaxies into different morphological types, and obtaining an excellent fit to the morphology-mass relation. We find that an accurate match to the observed correlation between stellar disk scale length and mass at z~0.0 requires that the gas loses 20% of its initial specific angular momentum to the corresponding dark matter halo during the formation of the cold gas disk. With this assumption, we reproduce the observed trends between the stellar mass and specific angular momentum for both disk- and bulge-dominated galaxies, with late-type galaxies rotating faster than early-types of the same mass. We include dissipation of energy in gas-rich mergers, thus reducing the merger remnant sizes, which allows us to match the observed mass-size relation for bulge-dominated systems. Finally, we present the baryonic Tully-Fisher relation for gas- and disk-dominated galaxies, and find that our trend agrees well with the present-day observational constraints.