The Star Formation Rate Intensity Distribution Function: Implications for the Cosmic Star Formation Rate History of the Universe

We address the effects of cosmological surface brightness dimming onobservations of faint galaxies by examining the distribution of "unobscured"star formation rate intensities versus redshift. We use the star formation rateintensity distribution function to assess the ultraviolet luminosity densityversus redshift, based on our photometry and photometric redshift measurementsof faint galaxies in the HDF and the HDF--S WFPC2 and NICMOS fields. We findthat (1) previous measurements have missed a dominant fraction of theultraviolet luminosity density of the universe at high redshifts by neglectingcosmological surface brightness dimming effects, which are important atredshifts larger than z = 2, (2) the incidence of the highest intensity starforming regions increases monotonically with redshift, and (3) the ultravioletluminosity density plausibly increases monotonically with redshift through thehighest redshifts observed. By measuring the spectrum of the luminosity densityversus redshift, we also find that (4) previous measurements of the ultravioletluminosity density at redshifts z < 2 must be reduced by a factor 2 to allowfor the spectrum of the luminosity density between rest-frame wavelengths 1500and 2800 A. And by comparing with observations of high-redshift dampedLyman-alpha absorption systems detected toward background QSOs, we further findthat (5) the distribution of star formation rate intensities matches thedistribution of neutral hydrogen column densities at redshifts z = 2 through 5,which establishes a quantitative connection between high-redshift galaxies andhigh column density gas and suggests that high-redshift damped Lyman-alphaabsorption systems trace lower star formation rate intensity regions of thesame galaxies detected in star light in the HDF and HDF--S.Comment: 28 pages, 9 figures; accepted for publication in the Astrophysical Journa