Canada-France Redshift Survey. XIV. Spectral Properties of Field Galaxies up to z = 1

The spectral properties of more than 400 Canada-France Redshift Survey (CFRS) galaxies and their changes over the redshift interval 0 ? z ? 1.3 are investigated. Emission-line intensities and equivalent widths for accessible lines have been measured, as well as continuum color indices based on 200 ? wide spectral regions. Within the CFRS sample, the comoving fraction of galaxies with significant emission lines [W0(O II) > 15 ?] increases from about 13% locally to over 50% at z > 0.5. The fraction of luminous (MB 0.5, the latter fraction being similar to that of early-type galaxies at that redshift. There is considerable evidence in the data presented here that star formation increases from z = 0 to z > 0.5 in disk galaxies. However, the absence of extremely blue colors and the presence of significant Balmer absorption suggests that the star formation is primarily taking place over long periods of time, rather than in short-duration, high-amplitude bursts. There are several indications that the average metallicity and dust opacity were lower in emission-line galaxies at high redshift than those typically seen in luminous galaxies locally. Beyond z = 0.7, almost all the emission-line galaxies, including the most luminous (at 1 ?m at rest) ones, have colors approaching those of present-day irregular galaxies, and one-third of them have indications (primarily from the strength of the 4000 ? break) of metallicities significantly less than solar (Z < 0.2 Z?). It is argued that changes in metallicity and dust extinction could be contributing to the observed evolution of the line and continuum luminosity densities, the luminosity function, and/or the surface brightnesses and morphologies of galaxies in the CFRS. If the Kennicutt (1992) relation is used to convert the large increase in the comoving luminosity density of [O II] 3727 back to z ~ 1 into a star formation rate, then it implies a present stellar mass density in excess of that observed locally. This result suggests that the Kennicutt relation is inappropriate for the CFRS objects, perhaps because of the changes in their metallicities and dust opacities and/or in their initial mass functions. Using the Gallagher et al. (1989) relation for objects having colors of irregular galaxies reduces the production of long-lived stars since z = 1 to 75% of the present-day value. More complex mechanisms are probably responsible for changes seen in the emission-line ratios of H II regions in CFRS galaxies, which show higher ionization parameters than local H II galaxy ones. This change could be due to a higher ionizing efficiency of the photons from hot stars in galaxies at high redshift.