Other
Scientific paper
Jun 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008phdt........20b&link_type=abstract
Proquest Dissertations And Theses 2008. Section 0250, Part 0606 216 pages; [Ph.D. dissertation].United States -- Washington: Un
Other
Disk Galaxies, Galaxy Formation, Galaxy Evolution, Gas Accretion, N-Body
Scientific paper
The role of cold flow gas accretion in the formation and evolution of galaxies is examined using very high resolution N-Body+SPH simulations. Three different approaches to study gas accretion: (1) Four simulated galaxies were selected to study gas accretion and stellar disk growth across two orders of magnitude in halo mass, from 3×10^10 [Special characters omitted.] to 3×10^12 [Special characters omitted.] . (2) Another six L* galaxies were chosen to have a range of spin parameter values and merger histories in order to study the effects of cold gas accretion on stellar disk growth at a given halo mass. (3) Three additional simulations of galaxies that reach a few ×10^11 to 10^12 by z = 4 were studied to investigate cold flows in massive galaxies at high redshift. For all of these galaxies, gas accretion is dominated by smooth gas that never belonged to another galaxy halo.
The fraction of smoothly accreted gas that is shocked as it enters the virial radius and flows toward the central galaxy is a strong function of galaxy mass. When present, cold gas accretion dominates the star formation of these galaxies. Cold flow gas accretion leads to both large star formation rates at early times for massive galaxies, and to the early building of stellar disks in L* galaxies. We argue that the addition of cold flow gas accretion, particularly in filaments, to existing semi-analytic models will reduce their strong dependence on mergers to reproduce observed star formation rates and colors at high redshifts. If our unshocked gas is instead shock heated as it enters the virial radius, as adopted by analytic models of galaxy formation, the growth of the disk is delayed until z~1.
Finally, the fate of gas once cooled inside of galaxy disks is studied. Low star formation efficiencies, regulated by supernovae feedback, are primarily responsible for the lower metallicities of low mass galaxies. Low mass galaxies may lose a majority of their baryons, but they are still the most gas rich objects in our simulations due to their low star formation efficiencies.
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