The various techniques for discovering active galaxies are reviewed, the main emphasis being on optical techniques and their application to emission-line galaxies with active nuclei. The three principal sets of selection criteria involve morphology, colours and emission lines. The major extant lists of emission line galaxies are summarized. Problems of detection are discussed, including selection effects and the use of automatic plate measuring machines. The difficulties of generating useful statistics on different classes of objects are highlighted, but no attempt is made in deriving new statistics or to summarize those in the literature.

The history of the First Byurakan Survey carried out to search for AGN is shortly described. The sample completeness for different classes of objects: Sy1, Sy2, QSO, BL Lac objects is estimated as 0.6, 0.4, 0.4 and 0.6, respectively. The lack of radioquiet BL Lac objects as a whole class is shown. Different search procedures of AGN are compared, their perspectives are evaluated.

The method of the Second Spectral Survey carried out with the Byurakan 1-m Schmidt telescope is discussed. The limiting magnitude is fainter in comparison with the First Byurakan Survey at about 2–3 m .

The results of low dispersion (500 objects) and slit spectroscopy (300 objects) based on observations with the 6-m telescope of Special Astrophysical Observatory for four fields of the Second Survey are presented.

The luminosity function of faint UV galaxies is discussed. The completeness of AGN of the Second Survey and their surface and space densities are also estimated. The surface density of QSO and ELG is estimated and these data are compared with the results of other surveys.

New observational data obtained with the 6-m telescope are compared with the new data of different deep surveys carried out during last years.

We have detected 3, 141 ultraviolet-excess galaxies in the sky area of some 1,500 square degrees by means of the UGR three-image photographs taken with the 105-cm Kiso Schmidt. For each of these galaxies which we call KUGs the morphological type and the degree of ultraviolet-excess are given in the catalogues. The frequency distribution for these characteristics of KUGs is shown in a form of histogram. The results of a spectroscopic study for the 57 selected KUGs are that 85% of the sample have emission-lines and most of them are situated in the domain of HII regions on the emission-line ratio diagram.

The results of objective-prism spectrophotometry for a sample of quasar candidates investigated in an area of approximately 100 deg2 of sky are presented. The selection effects and the collective properties of the sample are discussed in terms of the consequences for the present understanding of the cosmological evolution of the quasar luminosity function.

The observational program “Deep spectral survey of the selected sky areas” on the 6-meter telescope is described. Preliminary results for the central part of field SA57 are discussed. The spectrum of a QS0 with probable redshift z=3.87 is presented. The number of quasars per sq. degree is estimated to be 470–675 to B < 23 mag., which gives the same slope in the increasing number of QSOs with magnitude as in brighter samples.

The use of objective prisms in conjunction with the large area coverage afforded by Schmidt telescopes provides a very powerful means of detecting large numbers of emission-line galaxies, and allows one to study their large scale distribution. An important question that has yet to be fully addressed is the relationship between the number-magnitude distributions of the normal field galaxy and emission-line galaxy populations. A comparison such as this would effectively probe the evolution with time of these active objects. For example, study of the distant (z = 0.458) cluster of galaxies associated with 3C 295 (Dressler & Gunn 1983) indicates that emission-line objects may have been far more numerous in the past than at present. As a preliminary investigation in advance of a larger project, we report here on a search for emission-line galaxies in four United Kingdom 1.2m Schmidt Telescope (UKST) objective prism fields.

Preliminary results of a study of automatically detected variable objects are presented.

The sample is divided into stellar and diffuse objects and the corresponding integrated counts as a function of magnitude are evaluated and compared with results in the literature.

At the present time the previously used term “Peculiar galaxy” is gradually being replaced by the term “active” galaxy. This is quite natural, because the overwhelming majority of “peculiar” galaxies turned out to be “active” at the same time. The opposite is not correct: there are a lot of examples where a galaxy looking normal is physically active.

The number of galaxies with UV excess relative to normal galaxies is determined and other statistical characteristics of galaxies with UV excess are also presented.

V.A. Ambartsumian's idea of the activity of galaxy nuclei, suggested 30 years ago, has played a great role in the development of extragalactic astronomy. He showed that the evolution of galaxies depended on the activity of their nuclei. According to Ambartsumian (1958) the nuclei of galaxies are active if explosions take place in them. These explosions lead to large radio fluxes and in general to the wide range of phenomena normally associated with nuclear activity.

The spectra of active galaxies show ultraviolet (UV) excess and emission lines of hydrogen and other elements. In other words, the UV excess and emission lines which are observed in the spectra of galaxies are the consequence of active processes.

From 1344 Markarian galaxies lying in the same area covered by Markarian survey and CGCG, 592 are positioned within the contours of Zwicky clusters. On the basis of these data statistical investigation of the relation of Markarian galaxies with Zwicky clusters is carried out. Markarian galaxies take part in the tendency of clustering of galaxies and they lie in any type of Zwicky clusters. Markarian galaxies coincide with greater probability with medium compact clusters than with open ones where they follow the distribution of normal galaxies. In medium compact and compact clusters they appear near the centres of concentration of galaxies but probably not in their dense cores.

The statistical study of the U-B, B-V colours of the central regions of galaxies of different Byurakan classes show the presence of UV-excess emission in the nuclear regions of the majority of galaxies of types 5 and 2s.

The purpose of this contribution is to compare the morphology of galaxies with UV-continuum (Markarian galaxies) found in the First Byurakan Survey with normal galaxies. We use only data from general surveys.

Most galaxies with UV-continuum avoid clusters of galaxies (Lipovetsky 1986). Until recently, however, it was difficult to compare spatial distribution of galaxies with UV-continuum with galaxies of other morphological types, since the number of galaxies with known distances was too small. Rapid accumulation of complete redshift samples in large areas of sky (Huchra 1985) makes such study now possible.

Blinking several pairs of U and B Tautenburg Schmidt plates (area ≈ 90□°) 1131 UV excess objects (B ≲ 21, U-B≲0.0) were found with projected distances R ≳ 15 kpc from the M 31 centre. The objects were investigated by U, B, V, r, i photometry and partly by Tautenburg objective prism plates and by image tube spectrographs (Tautenburg, Zelenchukskaya) with Drs. AFANAS'EV, KOPYLOV, NOTNI, LORENZ.

Recent optical work on Seyfert galaxies is summarized, particularly on their spectral classification, morphology, companions, and presence in clusters of galaxies. Their general continuity with QSOs and with Liners is emphasized. Methods of finding additional Seyfert galaxies and of assembling a complete sample for investigating the luminosity function of AGNs are also discussed.