Semi-analytic Modelling On The Formation And Evolution Of Disk Galaxies

In the current paradigm of galaxy formation, disk galaxies are assumed to formby cooling and condensation of baryons within dark matter halos with the two basicassumptions that baryons trace the same density profile and the same specific angularmomentum distribution as those of dark matter halos initially. Baryons will conservetheir angular momentum during the formation of disks. Although the globalobservational properties of disk galaxies, such as the luminosity function, the sizedistribution, etc., can be well understood within the framework by either analytical orsemi-analytical work, or numerical simulations, there still exist some poorly knownprocesses such as supernovae feedback, gas outflows, etc. The major goal of thepresent thesis is to investigate formation and evolution of disk galaxies through somedetailed studies including the formation and evolution of a Milky Way-type galaxy,the angular momentum problems in the current theoretical paradigm. The outlines ofthe thesis and the main conclusions are briefly summarized as follows. With more and more observational data being available, such as Sloan digital SkySurvey (SDSS) and the future LAMOST Project, the major observational propertiesof disk galaxies are listed in Chapter 1, which includes masses, luminosities, colors,sizes, and number densities, etc. Some important empirical correlations, for instance,the Tully-Fisher relation, are introduced as well. In Chapter 2, the current standardparadigm of galaxy formation and evolution is reviewed with the introductions ofcosmology, perturbation theory, dark matter halos, gas, formation of disk galaxies,and so on. As one of the most important parts of this thesis, a semi-analytic model for theformation and evolution of a Milky Way-type disk galaxy is investigated in Chapter 3 VAbstractwithin the current framework of disk galaxy formation. Gas infall, star formation,supernovae feedback, galactic winds and mass outflows are incorporated in the model.To be more realistic than previous work, the mass-accretion history and the structureproperties of the adopted halo are taken into account based on the recent numericalsimulation done by Zhao et al (2003). The specific angular momentum distributionof a dark halo is adopted as that suggested by Bullock et al (2001) in LCDM. Thetreatment for the galactic winds and mass outflows is based on the analytic modelsuggested by Shu, Mo & Mao (2003). It is found that our model predictions, such asthe rotation curve, masses of the disk and bulge, chemical evolution, etc, can roughlymatch most of the current observational results of the Milky Way Galaxy. However, it should be noted that there still exist a series of problems aboutangular momentum among analytic models, semi-analytic models and numericalsimulations, which include the angular momentum catastrophe and the mismatch ofangular-momentum profile. They display the important challenges to the standardparadigm of disk galaxy formation. In Chapter 4, we describe in detail two maincategories of angular momentum problems and summarize the methods that couldsolve these problems. Moreover, we discuss the resulted surface-density profilesaccording to the theoretical angular momentum distributions (AMDs) presented byBullock et al (2001) in both spherical and cylindrical coordinates and compare withthe observations of the Milky Way to clarify the angular momentum problems. Inorder to solve these angular momentum problems, we investigate the AMD in aresulted galactic disk under the new galaxy formation model with preheatedinter-galactic medium (IGM) suggested by Mo & Mao (2003). Comparing with theobservational results of 14 galaxies, we conclude that the galaxy formation modelwith preheated IGM could be a good approach to solve the problems of both "theangular momentum catastrophic" and "the mismatch of angular-momentum profiles"in current disk galaxy formation models. The...