Star formation at high redshift: The confrontation between theory and observations

Details Star formation at high redshift: The confrontation between theory and observations Star formation at high redshift: The confrontation between theory and observations

Feb 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007phdt.........1i&link_type=abstract

Proquest Dissertations And Theses 2007. Section 0098, Part 0606 234 pages; [Ph.D. dissertation].United States -- Maryland: The

Computer Science

1

Star Formation, Redshift, Galaxies, Lyman-Break Galaxies

Scientific paper

We investigate properties of Lyman-break galaxies by statistically comparing photometric observations with predictions derived from semi-analytic models based on the LCDM theory of hierarchical structure formation. We construct samples of U , B 435 , and V 775 -dropouts produced by GOODS, and complement the ACS optical B 435 , V 606 , i 775 , and z 850 data with the VLT ISAAC J, H, and K s and IRAC 3.6, 4.5, 5.8, and 8.0 observations. We produce model dropout galaxies derived from semi-analytic model runs, where parameters controlling star formation and dust content are varied. We then construct model density functions and convolve them with observational scatter derived from Monte-Carlo simulations. We find the best-fit models by computing likelihoods using the data and model dropouts and the UV-continuum and Balmer-break color-magnitude diagnostics. We find that we cannot discern among models with varying starburst efficiencies due to data limitations. However, we do favor models with enhanced quiescent star formation. Our best-fit models rule out any strong dependence of quiescent star formation on circular velocities. We also favor dusty models. Using the best-fit models we present predictions for the stellar masses, SFRs, and ages of the z ~ 3, z ~ 4, and z ~ 5 Lyman-break samples. We find that even though the current optical surveys are effective at selecting UV-bright, massive galaxies, they fail to select most of the stellar mass, which remains hidden in UV-faint and moderately massive galaxies. Our best-fit models predict a ~70% mass build-up between the z ~ 4 and z ~ 3 epochs for UV rest-frame L* galaxies, and a smaller, ~50%, build-up between the z ~ 5 and z ~ 4 epochs. This implies an on-going process of quite active stellar-mass assembly between the z ~ 5 epoch and the z ~ 3 epoch. Furthermore, for the z ~ 3 sample, the stellar masses range from 10 8 to 10 10 [Special characters omitted.] , roughly 1.5 orders of magnitude less than the stellar masses of the present day L [low *] spirals and ellipticals--this indicates that the z ~ 3 Lyman-break galaxies are not the fully assembled progenitors of the present-day L > L [low *] galaxies. Finally, we find that quite a few of the z ~ 5 galaxies have stellar masses of >10 10 [Special characters omitted.] , and that the median age of the z ~ 5 population is 240 Myrs. This points to an already active star formation well before the z ~ 5 epoch.

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