Incorporating Morphological Types into Semi-analytic Schemes for Galaxy Formation

In this review, I give a brief summary of galaxy evolution processes in hierarchical cosmologies and of their relative importance at different masses, times, and environments. I remind the reader of the processes that are commonly included in modern semi-analytic models of galaxy formation, and I comment on recent results and open issues.

A major goal of contemporary astrophysics is understanding the origin of the most massive galaxies in the universe, particularly nearby ellipticals and spirals. Theoretical models of galaxy formation have existed for many decades, although low and high redshift observations are only beginning to put constraints on different ideas. We briefly describe these observations and how they are revealing the methods by which galaxies form by contrasting and comparing fiducial rapid co...

We give a brief review of current theoretical work in galaxy formation. Recent results from N-body and N-body/hydrodynamic simulations, and from semianalytic modelling are discussed. We present updated versions of some figures from Cole et al (1994). In particular, we show the effect of using the revised stellar population synthesis model of Bruzual and Charlot, which results in a much better match to the observed colour distribution of galaxies than before. We also compare t...

Using semi-analytical models of galaxy formation, the origin of boxy and disky elliptical galaxies is investigated. We find that the simple scenario, motivated by N-body simulations, in which the isophotal shape is only dependent on the mass ratio of the last major merger, is not able to reproduce the observation that the fraction of boxy and disky ellipticals depends on galaxy luminosity. The observations can however be reproduce with the following reasonable assumptions: (i...

We present a phenomenological model for understanding the origins and evolution of galaxy morphologies from a phenomenological perspective. The model includes an observationally motivated prescription for star formation in galaxy disks, as well as a merger-driven starburst mode of star formation. We consider the formation of bulges and ellipticals both in mergers and by global instabilities in disks. We use our model to investigate the fundamental properties of disk galaxies ...

We examine in detail the dynamical structure of an elliptical galaxy simulated in the Lambda CDM scenario. The morphology of the galaxy evolves dramatically over time in response to the mode and timing of mass accretion; smooth deposition of cooled gas leads to the formation of centrifugally supported disks, whilst major mergers disperse stellar disks into spheroids. These two modes of accretion alternate successively until z~0.6, when the galaxy undergoes one last major (1:2...

In a sample of about 45,700 early-type galaxies extracted from SDSS, we find that the shape, normalization, and dispersion around the mean size-stellar mass relation is the same for young and old systems, provided the stellar mass is greater than 3*10^10 Msun. This is difficult to reproduce in pure passive evolution models, which generically predict older galaxies to be much more compact than younger ones of the same stellar mass. However, this aspect of our measurements is w...

The explanation for the existence of an excess population of faint blue galaxies (FBGs) has been a mystery for nearly two decades, and remains one of the grand astronomical issues to date. Existing models cannot explain all of the observational data such as galaxy number counts in the optical and infrared passbands and the redshift distributions of galaxies. Here, by modelling the morphological number counts derived from the Hubble Space Telescope, as well as the number count...

(Abridged) We develop and test a model for the cosmological role of mergers in the formation and quenching of red, early-type galaxies. Making the ansatz that star formation is quenched after a gas-rich, spheroid-forming major merger, we demonstrate that this naturally predicts the turnover in the efficiency of star formation at ~L_star, as well as the observed mass functions/density of red galaxies as a function of redshift, the formation times of spheroids as a function of ...

Recent studies have shown that massive galaxies in the distant universe are surprisingly compact, with typical sizes about a factor of three smaller than equally massive galaxies in the nearby universe. It has been suggested that these massive galaxies grow into systems resembling nearby galaxies through a series of minor mergers. In this model the size growth of galaxies is an inherently stochastic process, and the resulting size-luminosity relationship is expected to have c...