In this review I try to show the important role of the Byurakan Observatory in the discovery and detailed investigations of ultlaviolet excess (UV) galaxies, which are now the center of attention of many observatories. Most new Seyfert (Sy) galaxies by the end of the 1960s, when no more than ten of this type of galaxy were known, were discovered among UV galaxies. In addition, many unusual and interesting galaxies were also discovered among UV galaxies: double and multiple nucleus galaxies, double nucleus Sy galaxies, galaxies with jets, galaxies consisting only of Superassociations (giant HII regions), Sargent-Searle objects, BL Lacs and QSOs possessing a different type of activity according to Ambartsumian. The material presented here overlaps considerably that of some other talks delivered by the author in IAU Symposia Nos. 121 and 194.

This contribution reviews the properties of nuclear activity in nearby galaxies, with emphasis on results obtained from current optical surveys and multiwavelength follow-up observations thereof.

On the basis of the Second Byurakan Survey (SBS) we have produced the largest and most homogeneous new complete samples of faint Markarian galaxies, Sy galaxies and bright QSOs. The General Catalogue of the SBS Survey, which is completed and prepared for publication, contains the data for more than 3600 objects, half of which are star-like objects while the other half are galaxies. Nearly 2500 slit spectra were obtained for about 2100 SBS objects. 561 new QSOs and AGNs in the magnitude range 15.5 < B < 19.5 with redshifts 0.0 < z <3.2 were spectroscopically confirmed. A sample of 17 BLL has been isolated as well.

The volume for reliable investigation of faint Markarian UVX galaxies has been extended out to a distance of about ~ 500 Mpc, more than 50 times deeper than in the FBS. Faint Markarian UVX galaxies from the SBS survey comprise ~ 12% of field galaxies, slightly greater than in the First Markarian survey; ~ 10% of them (~ 120) turned out to be Sy galaxies.

A complete sample of faint (B ≤ 17.0, z ≤ 0.1) Sy galaxies has been constructed. In the spatial volume with radius of about 500 Mpc, the relative number of AGNs is 1.2% of field galaxies. One of the most complete and representative samples of bright QSOs (~ 130) in the magnitude range 15.7 < B ≤ 17.5 with redshifts 0.3 ≤ z ≤ 2.2 has been constructed as well.

The objects in the combined complete sample of SBS Sy galaxies and QSOs might be roughly divided into two groups: classical Sy galaxies and QSOs in agreement with the previous classification scheme and nonclassical SyG and QSOs for which the existing classification scheme is not sufficient for their classification. The presence of narrow line QSOs (NLQSOs) or so-called QSO II type objects is established. There is a continuous transition of all properties between all types of Sy galaxies and QSOs, from Liners through Sy2, NLSyls, BLSyl to NLQSOs and BLQSOs.

Preliminary results from the Multiwavelength AGN Survey (MWAGN) in X-ray, Radio and IR wavebands in the SBS area are presented. The MWAGN survey in the SBS area shows that the ROSAT or FIRST surveys by themselves cannot represent the whole AGN/QSO sample. The ROSAT Bright sources along with the FIRST sources comprise only 25% of the whole SBS QSO sample. The IRAS survey is effective for a redshift less than z < 0.05. All classical Sy2s but only ~ 50% of classical Syls are IRAS sources. Luminous and Ultraluminous IRAS SBS AGNs comprise ~ 25% of the whole AGN sample. The greater part of SBS AGN/QSOs are neither ROSAT nor FIRST nor IRAS LIG or ULIG sources. They are optically emitting AGN/QSOs.

The multiwavelength “complete” sample of bright QSOs in the SBS area allows us to conclude that the fast evolution of bright QSOs is more likely the result of a selection effect than the result of fast cosmological evolution. The LogN-B relation for these QSOs reduces to the value LogN − B = 0.67 ± 0.005.

A direct empirical estimate of the effect of overlapping images is obtained from the MWAGN survey. The effect of overlap comprises ~ 5% for QSOs brighter than B ≤ 17.0 and ~ 10% for QSOs brighter than B ≤ 17.5.

Over the past decade, our team has pursued a quest to search for the optically brightest quasars in the entire extragalactic sky, by means of automated quasar selection using digitised objective prism spectra. We give a brief overview over the observational database and selection strategies and present some of the major survey highlights

Objective-prism surveys for UV-excess and emission-line objects, especially the First and Second Byurakan Surveys, have been central to the study of active galactic nuclei (AGNs). We review previous line-selected surveys for AGNs and discuss their contribution to our understanding of the AGN phenomena. In addition, we present results from the KPNO International Spectroscopic Survey, a modern digital objective-prism survey for emission line objects. This survey is discovering substantial numbers of new AGNs, in particular low-luminosity AGNs and LINERs.

The US Bright Quasar Sample (UBQS) is a color-selected sample of quasars with B < 17 that has been constructed with an eye towards completeness within well-defined selection limits. The redshift distribution of the UBQS shows an interesting spike at z ~ 0.55. The significance of this enhancement increases when the UBQS is combined with other bright quasar samples which also show evidence of high levels of completeness. Reconstitution of this combined bright quasar sample after removal of the emission-line flux from the B magnitudes indicates that the z ~ 0.55 spike is not caused by an emission-line selection bias. Rather, the largest effect of these sample corrections would be to depress the high end of the optical luminosity function that is derivable from this combined sample.

I summarise a few recent results on the evolution of optically selected QSOs, with special emphasis on the notoriously difficult but physically important extremes at low and high luminosities and redshifts. It seems that quasar evolution is a more complex phenomenon than has often been assumed, and the new generation of surveys is just about to make this visible.

We report on a search for QSOs via variability and zero-proper motion. Candidates were selected by means of indices for overall variability, long-term variability, proper motion and image structure measured on a large number of Schmidt plates with a time-baseline of three decades. Spectroscopic follow-up observations of the candidates brighter than the pre-estimated completeness limit, Blim ≈ 19.7, of the survey revealed about 200 QSOs and Seyfert 1s with redshifts z ≈ 0 — 3. We describe the survey strategy and discuss the properties of the resulting QSO sample.

Preliminary results are presented for a spectroscopic survey of the Groth Survey Strip (GSS), a 30 by 3 arcminute region of the sky imaged with HST, for which several hundred galaxy spectra have been obtained as part of the DEEP project (http://deep.ucolick.org). At least 6 broad-line AGNs (primarily Seyfert 1s) have been detected as well as several narrow-line Seyfert 2 candidates. The seyfert galaxies detected in our survey have integrated absolute magnitudes extending to MB ~-17.5, probing fainter magnitudes and higher redshifts than existing optical spectroscopic surveys. We also discuss a variablity study of the GSS using the original HST images from 1994 and new images obtained in 2001. The high resolution obtained with HST allows us to isolate and measure variable galactic nuclei too faint to be detected from the ground, reaching nuclear magnitudes of MB~-16 in galaxies to z~0.8. The combination of these techniques provide a powerful probe of the population of low-luminosity AGNs at moderate redshifts.

We performed a new analysis of the В and R light curves of a sample of PG QSOs. We confirm a variability-redshift correlation and its interpretation in terms of spectral variability. We find an intra-QSO and an inter-QSO α;-L correlation. The former can be explained neither by presence of the host galaxy nor by changes of the accretion rate. Hot spots due to accretion disk instabilities could explain the observations.

The results of CCD spectroscopic observations of Shakhbazian compact groups of galaxies (SHCGs) with the 1.54-m (La Silla, Chile), 2.2-m (Calar Alto, Spain) and 2.6-m (Byurakan) telescopes are presented. According to these preliminary data, about 10% of member galaxies in SHCGs are emission-line galaxies (ELGs) including the broad-line AGNs (of classical Seyfert 1 type) and the narrow-emission-line galaxies.

A research program has been developed in the University of Potsdam, Potsdam Astrophysikalisches Institut in cooperation with other observatories (particularly with Byurakan Astrophysical Observatory) to perform photometric and spectroscopic investigations of galaxies in the SHCGs. Within the framework of this program the redshift (radial velocity) measurements have been carried out for more than 200 galaxies in 36 SHCGs. The MIDAS software package was used for processing and interpreting of the galaxy spectra. Most of these redshifts were measured for the first time. 180 member galaxies (90%) in these groups have absorption spectra typical of E and SO galaxies. Twenty galaxies (10%) turn out to be ELGs. They are in the range 0.02 ≤ z ≤ 0.17, i.e., the SHCGs lie in approximately the same redshift space as Abell clusters. These compact groups contain predominantly elliptical and lenticular galaxies (del Olmo 1988; Amirkhanian 1989) like the cores of rich, regular, centrally condensed clusters of galaxies. The fraction of spirals falls in the densest matter concentrations. On the other hand, it is a well-established fact that in the local universe the active objects tend to avoid the cores of dense clusters of galaxies (e.g. Green and Yee 1984). That is why the discovery of an emission-line population with broad-line AGNs in SHCGs (Tiersch et al. 1999) was unexpected. As shown by Dressier, Thompson and Shectman (1985) in their sample of 1268 galaxies in the feilds of 14 rich clusters the ELGs comprise 31% of the field galaxies but only 7% of the cluster galaxies. Similarly, according to their statistics AGNs make up 5% of the field sample, but only 1% of the cluster sample. They note that the difference in the distribution of morphological types can only partially explain this effect. Obviously, some sort of environmental influence is present.

We present preliminary results of an optical survey of a spectroscopically selected sample of nearby AGNs (z < 0.1). The aim of the program that we are currently carrying out is to demonstrate that the activity phenomenon is strongly related to galaxy interactions. In detail, we want to study the morphology of our sample of galaxies in order to reveal the presence of features like bars, rings, double nuclei, isophotal distortions and tidal tails, most of which are not detectable on the POSS plates. The work is based on the analysis of broad band B, V and R images, the study of their photometric parameters and the results of the application of a Laplacian adaptive filter, able to enhance hidden and faint structures.

It is clear now that morphological criteria don’t divide galaxies from QSOs. Many galaxies are stellar-like objects and, conversely, quasars have host galaxies of various luminosities. For instance, two objects - SBS 1120+586A and SBS 1123+598 - absolutely do not differ from stars on the charts of the POSS and were classified as BSO-type. But they turned out to be galaxies with moderate luminosities (Markarian et al. 1988). Erastova (2000) produced a list of stellar-like galaxies from the SBS. Out of 339 KUV objects, 107 (31.6%) are emission-line galaxies of various luminosities (Darling & Wegner 1996). A considerable number of active galaxies appear among CSO - Case stellar objects. Conversely, objects having extended images on low-dispersion spectral plates turned out to be QSOs. SBS 1520+530 is a gravitationally lensed QSO with z=1.855 and on our low-dispersion plates appears as a galaxy (Chavushyan et al., 1997).

In this paper we compare the results of spectrophotometric observations for more then 40 emission line galaxies (ELG) without UV-excess and 70 galaxies with UV-excess (UV-galaxies) from the Second Byurakan Survey (SBS) carried out with the scanner on the 6-m telescope of the Special Astrophysical Observatory. The comparison was aimed to answer the questions: are there any essential differences between these two types of galaxies? And what is the fraction of AGN among ELG and UV-galaxies? To answer this question we have investigated some physical parameters. Great care was taken in classifying the spectra of these galaxies as “HII region-like or “AGN-like” using a new diagnostic method for emission-line galaxies (Rola et al.). We find that 14% of emission line galaxies (ELG) have Sy2 and LINER-like spectra. The transition or ambiguous objects among them comprise 20%. The fraction of LINER-like and Sy2 objects among UV-galaxies is 21% while that of the transition or ambiguous objects in UV-galaxies is 28%. From SBS galaxies, 18% are Sy2s and LINER-like galaxies.

The results of follow-up spectroscopy completed for seven samples of SBS galaxies in selected fields are briefly presented.