Caltech Faint Galaxy Redshift Survey. XVI. The Luminosity Function for Galaxies in the Region of the Hubble Deep Field–North to z  =  1.5

Abstract

We have carried out a study of the luminosity function (LF) of galaxies in the region of the Hubble Deep Field-North using our very complete redshift catalog. We divide the sample into five redshift bins covering the range 0.01 < z < 1.5 and consider three primary galaxy spectral classes. We solve for the LF at four rest-frame wavelengths from 0.24 to 2.2 μm. We find that the LFs for quiescent galaxies have shallow faint-end slopes while those of galaxies with detectable emission lines have steeper faint-end slopes. Furthermore, these slopes appear to be independent of redshift out to z = 1.05 for each galaxy spectral grouping and agree well with comparable local determinations. We then fix α to obtain values of L* for each galaxy spectral grouping as a function of redshift. We find that galaxies with strong absorption lines become brighter with z with Q ~ 0.6 at all rest-frame bands studied here, where Q = Δ log [L*(z)]/Δz, while galaxies with detectable emission lines (i.e., star-forming galaxies) show a smaller change in L* with redshift at all bands, Q ~ 0.3, with Q becoming significantly larger at rest-frame 2400 Å. Passive evolution models of galaxies are in reasonable agreement with these results for absorption-line-dominated galaxies, while plausible star formation histories can reproduce the behavior of the emission-line galaxies. We find a constant comoving number density and stellar mass in galaxies out to z ~ 1.05. By stretching all the correction factors applied to the galaxy counts in the highest redshift bin to their maximum possible values, we can just barely achieve this between z = 1.05 and 1.3. The major epoch(s) of star formation and of galaxy formation must have occurred even earlier. The UV luminosity density, an indicator of the star formation rate, has increased by a factor of ~4 over the period z = 0-1.

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