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Buzzoni, A.:
"UV properties and evolution of high-redshift galaxies",
2003, proc. of the ASP Conf. Ser. no. 297, "Star Formation through Time" - Granada, Spain 24-28/Sep/2002, Eds. E. Perez, R. Gonzalez-Delgado, G. Tenorio-Tagle (ASP: San Francisco), p. 471

Summary:
I assess the problem of morphological and photometric evolution of high-redshift galaxies in the ultraviolet wavelength range. My discussion will partly rely on a new set of template galaxy models, in order to infer the expected changes along the Hubble morphological sequence at the different cosmic epochs. The impact of evolution on the faint-end galaxy luminosity function at z~1 and beyond will also be evaluated and briefly discussed.



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Figure 1 - Synthetic c-m diagrams for a 15 Gyr SSP of solar metallicity and Salpeter IMF, after Buzzoni (1989). The left panel shows the magnitude distribution of stars at 2000 Å, U(20), compared with the corresponding distribution in the Johnson R band (right panel). The histogram on the vertical axis displays the relative fraction to the integrated SSP luminosity from stars in the different magnitude bins. While in the U(20) diagram most of SSP luminosity is provided by stars around the turn off region, this is not the case for the R diagram, where there is a sizable contribution from Post-MS stars (i.e. horizontal branch, R-HB, and red giant branches, RGB+AGB)
Figure 2 - Theoretical calibration of star formation rate and 2800 Å integrated luminosity of a stellar population, after Buzzoni (2002). Thick solid line is the expected relationship for a Salpeter IMF with stars up to 120 M_sun. A change of the upper cutoff mass for M_up = 80, 60, 40 M_sun is diplayed by the thin parallel lines, as labelled. Dashed lines report the change in the IMF power-law slope (namely dN = A M**(-s)dM) for dwarf- (s = 3.35) and giant-dominated (s = 1.35) stellar populations. Dotted line is the corresponding calibration from Madau (1997) for a Salpeter IMF (s = 2.35) and M_up = 125 M_sun.
Figure 3 - The S/T morphological parameter, defined as L_(spheroid)/L_(tot), is studied at different ages for galaxies along the Hubble sequence. Left panel displays the present-day calibration (solid dots) at long wavelength, as derived from the data of Kent (1985; open dots), de Jong (1996; filled triangles), Giovanardi & Hunt (1988; filled squares), and Moriondo et al. (1998; open triangle and open squares). Its inferred trend in the Johnson U band is plotted in the right panel, according to the template galaxy models of Buzzoni (2002). The expected evolution for t = 1 Gyr clearly points to a strongly enhanced bulge contribution, especially for later-type spiral systems (Sc-Sd types), that would closely resemble present-day S0-Sa galaxies.
Figure 4 - Left panel reports the observed B luminosity function for low-redshift galaxies, according to Marzke et al. (1998; solid dots) and its partition among the different morphological types (spirals = open squares; ellipticals = triangles; irregulars = stars). The middle panel is the inferred galaxy distribution at 2000 Å, according to the U(20)-B colors from the Buzzoni (2002) template models, and its expected evolution at high redshift (z~1 to 3; right panel) for 5 Gyr galaxy models. Note that the U(20) galaxy distribution for t = 5 Gyr should roughly match the observed luminosity function at optical wavelength (~Johnson B to I bands). The B (solid line) locus along with the U(20) overal galaxy distribution at z = 0 (dashed line) (from left and middle panels, respectively) are overplotted in the right panel, for reference.



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AB/Jul 2003