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The APM QSO survey is a quantitative survey aimed at finding a large sample (∼ 1000) of QSOs using broadly-based selection criteria applied to machine-scanned UK Schmidt Telescope direct and objective-prism plates. The survey is currently entering its third year and, as of August 1988, the sample consists of ∼ 700 QSOs with mJ ≥ 18.75 in the range 0.2 ≤ z ≤ 3.3. Preliminary analysis suggests that the sample is relatively free of the selection effects endemic to most QSO surveys based on slitless spectroscopy.
Survey of surveys, and the place of the Second Byurakan Survey (SBS) among them is shortly discussed. Deep low-dispersion surveys cover > 10000 sq.degrees, but they managed to study only 15% of this area relatively well.
For 450 SBS objects the slit spectra were obtained on 6 m telescope of SAO. The nature of 120 QS0s,40 Sy galaxies and more than 200 ELG are confirmed. The results of the slit spectroscopy in six SBS fields covering commonly the area of ∼100 sq.degrees are presented.
All surveys, except Byurakan Surveys are extremely poor with Sy galaxies, that is their distinction from other surveys. Weak (16<m<18m5) SBS Sy galaxies sufficiently well filled in the interval between QSOs and Sy galaxies, the efficiency of selection does not much depend on redshifts. There is quite good pass from Sy galaxies to QSOs.
Four years ago we started at Cerro Calán an extension of the objective prism survey carried out at Cerro Tololo Inter-American Observatory (CTIO) by Malcolm Smith a decade ago (Smith 1975, Smith, Aguirre and Zemelman 1976). Thanks to the kindness of Dr. P.S. Osmer, then Director of CTIO, we got on loan Smith's original plate collection. Searching his plate material we learned to recognize the most prominent emission line objects. We decided then to extend Tololo's original survey to an area of the southern sky large enough to be of statistical interest but small enough so it could be carried through with our very limited facilities at Cerro Calán.
For some years, this author has suspected that certain small regions of the southern sky were “good fishing grounds” for finding Seyfert galaxies. It is now possible to follow up this suspicion, not only on the sky (see also Fairall 1979, Petrosian and Turatto 1986) but in three-dimensional space (with redshift assumed to indicate distance). Figure 1 (overleaf) is a sample of the plots obtained from a database of some 6200 galaxies, south of Declination −17.5° for which redshifts are available - including 199 Seyfert galaxies (Fairall and Jones 1988). The data is not ideal, since it lacks statistical control; but experience has shown it nevertheless to be reliable for galaxies in general, whilst it is hoped that few, if any, higher-luminosity Seyfert nuclei remain undetected.
In Barbieri and Cristiani (1986) the results of a preliminary objective prism survey in the SA94 were reported, in Barbieri et al. (1987) these results were compared with the colour survey of Mitchell et al. (1984). The study continued with the creation of a sample of UVX candidates in the 10 central square degrees of the field.
Radio, FIR, spectral and X-ray data by 11 parameters for the AGNs samples of Sy1, Sy1.5, Sy2 types and LINERs are compiled. All samples are processed by the multivariate statistical methods including factor and discriminant analysises. The following results are obtained:
– LINERs by principal factors, determining NLR and the central engine are clearly separated from the Seyfert galaxies.
– All types of the Seyfert galaxies in all have the same NLR.
– Intermediate Seyfert type is real. These AGNs are much more similar to Sy1 type objects than to Sy2.
Variability of QSOs serves not only as an independent search technique but also as another parameter to correlate with such properties as luminosity (in radio, optical, X-ray), redshift, spectral features, color, etc., so as to better understand AGNs. We present some preliminary results on a variability study of an essentially complete sample using 4 m prime focus plates of a 0.3 deg2 field at the North Galactic Pole (SA57). The faintness of our survey, B ≈ 23; the precision of the measurements (σ ≤ 0.05 mag); and the availability of redshifts for many of the candidates provide an opportunity to study QSO variability in regimes previously unexplored (c.f. Bonoli et al. 1979 or Hawkins 1986).
We have observed a homogeneous sample of Seyfert 1 and 1.5 galaxies with the aim to determine the luminosity function of Seyfert nuclei. Observations were made with the CCD cameras of Asiago and Loiano Observatories in B, V and R bands in order to isolate the contribution of different stellar populations. A photometric decomposition into three components (disc, bulge and nucleus) was fitted to the observed luminosity profiles to separate the nuclear and the host galaxy contributions and to understand whether underlying galaxies actually behave as “normal” galaxies.
The study of quasars clustering could become an important discriminant among different scenarios of the formation of large scale structure. The quasar clustering has now been confirmed and measured (Chu and Fang, 1986; Shaver, 1988) and the evolution of quasar clustering has been reported (Fang, Chu and Zhu, 1985; Chu and Fang, 1986). In the present work a large sample of about 3600 quasars in Hewitt-Burbidge catalog is employed and it is divided into several subsamples with different redshift ranges, a comparison of the correlation function in different subsamples provides then a mean of studying the evolution of the clustering with cosmology time.
Following the discovery by Djorgovski et al. (1985) of a companion to the high redshift quasar PKS 1614+051, we initiated a systematic search for such objects with the Danish 1.5 meter telescope at La Silla. The observing technique is CCD exposures in narrow filters (FWHM=100Å) centered on the redshifted Lyα. For an exposure time of 40 min. Our limiting magnitude is around 22.0 (where the r.m.s. error is approximately ±0.15), according to test runs with DAOPHOT. The aim of the search is to clarify the nature of such companions: are they “primordial” galaxies? Lyα clouds associated with the quasar? - and how frequent is such a phenomenon? Up to now we have covered 26 fields around quasars with redshift ≥3.0 (which is about 25% of all high redshift quasars in the Veron and Veron Catalogue). Furthermore 12 fields around z≈2.5 has also been observed (see Table 1). A quick visual inspection of all our frames has not revealed any companions except for the object found by Djorgovski et al. (which is easily picked up by our technique). However, a thorough photometric reduction (using DAOPHOT) might reveal fainter candidates. Taken together with the fields reported observed by Hu and Cowie (1987) and Djorgovski et al. (1987), a total of about 50 fields have so far been observed. The preliminary conclusion is therefore that such companions, whatever they might be, are very rare, and certainly much rarer than similar systems found around quasars of low redshift.
An all-sky 12μm flux-limited sample of 392 galaxies has been selected from the IRAS Point Source Catalog. More than 20% of the sample harbor active nuclei (with Seyfert 1 or 2 or LINER emission-line spectra). Thus one byproduct of this work is the definition of a large complete sample of bright active galaxies, with roughly equal percentages of Sy 1's, Sy 2's and LINERs. Since we now have virtually all (93%) the redshifts for the sample galaxies, the far-infrared luminosity functions of all classes of galaxies have been derived using IRAS coadded data. Since our luminosity functions for Sy 1 and Sy 2 are indistinguishable from those of the optically selected CfA sample, the 12μm selection appears to be an efficient and complete technique for finding active galactic nuclei. Optical spectrophotometry and near-IR photometry of the sample is being obtained to compute accurate bolometric luminosities.
The UV continuum spectrum is used to extract the mass (and accretion rate) of quasars and AGN, assuming the UV is dominated by the emission from a thin accretion disk. This is done by fitting the observed luminosity and spectral slope in the UV by an accretion disk mode, giving the accretion parameters (black hole mass and accretion rate). An independent estimate of the mass is obtained using the emission-line method, which assumes that the velocity dispersion of the broad emission-line s is induced by the gravitational potential of the central compact object. For a sample of 36 quasars and Seyfert 1 galaxies, for which both data, the UV spectrum and the Hβ line width are available, the masses calculated with the two independent methods are in good agreement (within a factor of 2 for 75% of the sample) and highly correlated. Over three orders of magnitude in luminosity, the mass is found to increase less than linearely with luminosity, being in the range 108 < M < 1010M⊙, with L(1450A)/LEdd ranging from 0.001 for Seyferts to 0.03 for bright quasars.
Recent observations of luminous IRAS galaxies (LIR > 1011 L⊙) have revealed that virtually all are extremely rich in molecular gas with H2 abundances 5–20 times that of the Milky Way, and deep CCD imaging indicates that most are recent galactic mergers. Interferometric observations at millimeter wavelengths for five of these galaxies demonstrate that approximately half of the interstellar matter is contained in the central kpc. This gas concentration can result in the formation of a massive central star cluster. The deep potential of the central star cluster and the high density of interstellar gas ensure that virtually all of the gas lost during late stellar evolution sinks to the center of the cluster, building up a central, massive black hole. For a coeval star cluster of 4×109 M⊙, a central mass of approximately 1.5×109 M⊙ will accumulate within approximately 108 years and accretion at an average rate of 7 M⊙ yr−1 over this time will result in a mean accretion luminosity of 1013 L⊙. This luminosity, radiated at X-ray and uv wavelengths from the inner accretion disk ionizes the mass loss envelopes of the surrounding red giant stars providing an origin for the broad emission line regions of QSO's. The large linewidths would then be due to orbital motion in the massive central star cluster.
This review discusses the present understanding of the inner region of AGN. Several fundamental questions are adressed, such as the determination of the central mass, the accretion rate and the presence or absence of massive accretion disks. The “standard model”, used until recently to deduce the density, ionization, geometry and other physical properties of AGN, is facing sever difficulties and several unsolved problems, such as the hydrogen line ratio, the FeII spectrum, the energy budget discrepency and the confinement of the broad line clouds may force us to abandon it all together. The new line-continuum reverberation measurements are perhaps the most important developement of recent years and their significance is discussed in relation to the other mentioned problems. Thin or thick accretion disks are likely to be present in the very center of AGNs. The theory of such disks is not advanced enough to provide accurate spectral calculations and the best way to identify them is to look for the signature of their nonisotropic radiation field in well selected samples. Several new developements and ideas, such as disk shaped emission line region, stars and stellar winds as broad line clouds, dust emission and very small-very dense BLR are also discussed.
The emission lines of OVV quasars can vary significantly within a month, more rapidly than expected from photoionization models. This can be explained by anistropic continuum emission and joins several other lines of evidence suggesting anisotropic emission of the optical /uv continuum in AGN.
Emission lines variability of Seyfert galaxy NGC 1275 nucleus in the scales of years and months has been observed since 1971 (I. Pronik, 1980). The photoelectric observations of I. Pronik and N. Merkulova (1987) show, that the variability in Hβ and 4959+ 5007 A [OIII] lines occurs also in the time scale of several days. Hereinafter the analysis of Hβ and [OIII] variable emission lines within months is presented according to photographic observations carried out from 1971 till 1982 by I. Pronik (1980), V. Doroshenko and V. Terebizh (1983) and K. Chuvaev (1985).