Slit spectra show that of the order of 1% of field galaxies are Seyfert galaxies, with emission lines roughly as strong as in the spectra of the classical objects of this type. Thus to find appreciable numbers of them to a faint magnitude limit by taking individual slit spectra would require prohibitive amounts of large-telescope time. The Markarian or First Byurakan Survey was an objective-prism survey based largely on ultraviolet excess, and about 10% of the galaxies isolated by it have turned out to be Seyfert galaxies (Lipovetsky, Markarian and Stepanian 1987). The other 90% are largely galaxies with H II-region type spectra. The Second Byurakan Survey, now underway, covers part of the same area with the same telescope, but with fine-grain plates in three different spectral regions (blue, green and red) to a fainter magnitude limit, and with various orientations of the prisms. Follow-up slit spectra of Seyfert candidates are then obtained with the 6-m telescope (Markarian, Stepanian and Erastova 1987). At Lick Observatory we have obtained spectra of some of the fainter galaxies identified as Seyferts in the SBS. In all these cases we agree that they are Seyfert galaxies, and in most cases of nearly the same types as classified by the Soviet astronomers.
Other low-dispersion objective-prism surveys have been carried out with the Michigan Schmidt telescope at Cerro Tololo by MacAlpine and various collaborators (see MacAlpine and Williams 1981), and with the Case Schmidt at Kitt Peak by Sanduleak and Pesch (e.g. 1987).
These surveys use relatively low dispersion, reach a relatively faint limit, and are based both on ultraviolet excess and the presence of emission lines, but the fraction of them that are Seyfert galaxies is significantly smaller than in the FBS.
Defining the "limit" of an objective-prism survey aimed at finding emission-line galaxies is difficult. It is not simply a single magnitude, but rather a combination of magnitude and the relative strength of the strongest emission line(s) with respect to the continuum. This point has been discussed most recently by Gratton and Osmer (1987) and by Salzer (1987).
A three-color photographic survey is being carried out with the Kiso Schmidt telescope of the Tokyo Astronomical Observatory by Takase and Miyauchi-Isobe (e.g. 1987). This survey also has led to the discovery of many blue galaxies, a large fraction of which have emission-line spectra. Again, most of these are HII-region type spectra, and only a small fraction are Seyferts (Maehara et al. 1986; Takase et al. 1987).
The IRAS color indices of known Seyfert galaxies indicate that they can be used to segregate partially these objects from other, "normal" galaxies (Miley, Neugebauer and Soifer 1985). This was expected from previous infrared studies of Seyfert galaxies, which showed that they contain large amounts of "warm" dust, near the active nucleus and heated by it. Many additional candidate Seyfert galaxies have been isolated using the IRAS color-index criteria developed in this way (de Grijp, Miley and Lub 1987). Slit spectra of these candidates have shown that a very large fraction of them are Seyfert 2s, many more heavily reddened than typical previously known objects of this type. Only a few previously unknown Seyfert 1s are among them, confirming that the optical objective-prism surveys have provided more nearly complete samples of these. All the candidates isolated by the IRAS color-index criteria are not Seyfert galaxies, but to date of those for which adequate slit spectra have been obtained and published, about 60% have proved to be Seyferts, about 10% to 15% LINERS, and about 25% to 30% reddened HII region galaxies (Carter 1984; de Grijp et al. 1985; Osterbrock and De Robertis 1985). The IRAS color-index criteria do not recover all previously known Seyfert galaxies.
In the Wasilewski field Shaw has to date found from the IRAS colors only one previously unknown Seyfert, IRAS 14434+2714, a Seyfert 2. I understand that Halpern, Bothun and Lonsdale have found two Seyfert 2s in this field from their IRAS color indices, but I have not seen a preprint of their paper. One of them may be the object named above.