We present a spectroscopic study of the 138 field galaxies to a redshift z =
0.3 from the I-selected Canada-France Redshift Survey. 117(85%) spectra exhibit
at least H alpha in emission, the remaining 21(15%) are purely absorption-line
spectra. We focus our analysis on spectra with H alpha and H beta in emission,
accounting for about half of this low-z sample, which we classify using
emission-line ratio diagrams. Using photoionization models, we determine the
extreme boundaries of H II galaxies in these diagnostic diagrams, and
demonstrate that the emission-line ratios of a significant fraction of galaxies
require harder photoionization sources than massive O stars. We find that about
17% of the field galaxies have emission-line ratios consistent with active
galaxies, e.g., Seyfert 2 or LINERs. After correcting for stellar absorption
under the Balmer lines, we conclude that the fraction of such galaxies is at
least 8% of the field galaxy population at z < 0.3.Comment: uuencoded compressed latex file including tables but not figures,
yielding 14 pages. The full text and figures are also available at
http://www.dao.nrc.ca/DAO/SCIENCE/science.html ,
http://www.astro.utoronto.ca/~lilly/CFRS/papers.html , and by anonymous ftp
at ftp://ast.cam.ac.uk/pub/lt . Accepted by MNRA
