Ultraviolet Properties of Primeval Galaxies: Theoretical Models from Stellar Population Synthesis

The ultraviolet luminosity evolution of star-forming galaxies is exploredfrom the theoretical point of view, especially focusing on the theory of UVenergetics in simple and composite stellar populations and its relationship tothe star formation rate and other main evolutionary parameters. Galaxy emission below 3000 Angstroms directly correlates with actual starformation, not depending on the total mass of the system. A straightforwardcalibration is obtained, in this sense, from the theoretical models at 1600,2000 and 2800 Angstroms, and a full comparison is carried out with IUE data andother balloon-borne observations for local galaxies. The claimed role of late-type systems as prevailing contributors to thecosmic UV background is reinforced by our results; at 2000 Angstroms Imirregulars are found in fact nearly four orders of magnitude brighter thanellipticals, per unit luminous mass. The role of dust absorption in the observation of high-redshift galaxies isassessed, comparing model output and observed spectral energy distribution oflocal galaxy samples. Similar to what we observe in our own galaxy, a quickevolution in the dust environment might be envisaged in primeval galaxies, withan increasing fraction of luminous matter that would escape the regions ofharder and "clumpy" dust absorption on a timescale of some 10^7 yr, comparablewith the lifetime of stars of 5-10 solar masses.