NEW DIAGNOSTIC METHODS FOR EMISSION-LINE GALAXIES IN DEEP SURVEYS

We present new quantitative classification methods for emission-line g alaxies, which are specially designed to be used in deep galaxy redshi ft surveys. A good segregation between starbursts and active galactic nuclei, i.e. Seyfert 2s and LINERs, is obtained from diagnostic diagra ms involving the [O II] lambda 3727 Angstrom, [Ne III]lambda 3869 Angs trom, H beta and [O III]lambda 5007 Angstrom relative intensities or t he [O II]lambda 3727 Angstrom and H beta equivalent widths. Furthermor e, the colour index of the continuum underlying [O II]lambda 3727 Angs trom and H beta provides an additional separation parameter between th e two types of emission-line galaxies. We have applied the equivalent widths method to the 0 < z less than or equal to 0.3 emission-line gal axies of the Canada-France Redshift Survey. Our results are in very go od agreement with those obtained using the standard diagnostic diagram s including all the strong optical emission-line intensity ratios.