Galaxy Formation: CDM, Feedback and the Hubble Sequence

Abstract

TreeSPH simulations of galaxy formation in a LCDM cosmology, with star formation, energetic stellar feedback and a meta-galactic UV field have been performed, resulting in realistic disk, S0 and E galaxies at z=0. The disk galaxies are deficient in angular momentum by only about a factor of two compared to observations for runs where fairly strong star-bursts in early, proto-galactic clouds lead to "blow-away" of the remaining gas. The surface density profiles of the stellar disks are approximately exponential and those of the bulges range from exponential to r^(1/4). B/D ratios and integrated B-V colours are consistent with observations. The observed I-band TF relation can be matched with M/L_I ~ 0.8, in fair agreement with recent determinations. The (E/S0)s have approximately r^(1/4) profiles, non disk-like kinematics and are flattened due to non-isotropic stellar velocity distributions. We predict hot halo gas to cool out and accrete onto the Galactic disk at 0.5-1 Msun/yr at z=0, consistent with upper limits from FUSE observations of O VI. We analyzed two Milky Way-sized galaxies and find accretion rates, and X-ray halo luminosities, 6-7 times larger at z=1 than at z=0. The gas infall declines nearly exponentially with time, supporting the approximation often used in chemical evolution models. The infall time-scales are comparable to what is used to solve the "G-dwarf problem". One disk forms "inside-out", the other "outside-in". For both, the mean stellar ages in the outskirts agree with findings for the disk of M31. The amount of hot gas in disk galaxy haloes is consistent with observational upper limits, as are dispersion measures to pulsars in the globular cluster M53 and the LMC, which were "inserted" in the disk galaxy haloes.