Some methods currently in use for the classification of the optical forms of the ‘compact’ galaxies and quasi-stellar objects are reviewed. It is shown that the category ‘Seyfert Galaxy’ is basically a spectroscopic (rather than a form) classification.

An optical form-classification is described which is, in principle, identical with published classification criteria for QSO, N-type, and compact objects. The importance of maintaining rigid form-standards is emphasized.

A brief description is given of methods used to find 745 compact galaxies in a 36 sq deg-field around M3. These constitute 24–40% of all galaxies in this area, brighter than 18.5 magnitude in B. Significant clustering found is related to Zwicky clusters of compact galaxies. Photographic 3-color photometry has been carried out. There seems to be no physical difference between cluster and field objects. The catalogue is to be published elsewhere, together with finding charts and detailed discussion of the photometry and statistics.

On the basis of their optical spectra, compact objects are divided into 3 classes according to the probable nature of their energy sources, as follows:

1. (1) Non-thermal: This class includes Seyfert nuclei, most N-type radio galaxies, and also very luminous Zwicky compact objects. The existence of high-velocity clouds, and a wide variety of densities and temperatures appear to be common characteristics of these objects. QSOs are considered to be related, with similar but more extreme properties.

2. (2) Hot, massive stars: This class includes some small galaxies, parts of galaxies or appendages to galaxies, which are usually much less luminous than class (1) objects.

3. (3) Stellar: Some compact galaxies having only absorption line spectra fall into this class.

A variety of morphological forms exists amongst class (1) and (2) objects.

Emission line spectra of QSOs are reviewed, and related to the physical conditions in the emitting regions.

Many features of the distribution of emission and absorption line redshifts of QSO spectra and of the distribution of the differences between emission and absorption line redshifts may be due to observational selection. However, it seems significant that all six of the absorption line objects of largest redshift have multiple absorption systems. Observations seem to favor more strongly the hypothesis that the multiple absorption line systems are due to clouds associated with the QSO rather than in the intervening space. The multiple absorption line systems of the QSOs PKS 0237–23, Ton 1530 and 4C 05.34 are discussed. The persistence of the Lyman-α absorption feature and identification of multiple-absorption line systems strongly suggests that unidentified absorption lines shortward of the Lyman-α emission also arise from the Lyman-α transition.

Studies of galaxies during the last seventy years have turned up a large array of peculiar objects. Vigorous work on these was rare until a few years ago when quasars were discovered. It then became clear that an understanding of quasars might come from an understanding of the less-extreme peculiar galaxies. It was further clear that even the physical processes occurring in nuclei of peculiar galaxies were far from easy to understand.

The wide absorption troughs of certain resonance lines in the spectra of the QSOs PHL 5200 and RS 23 are produced by pure scattering and must therefore be compensated by an equal amount of emission. Analysis of the transfer of resonance-line radiation through a differentially expanding atmosphere shows that the absorption-emission profiles can be quantitatively understood on this basis.

The profiles of the Balmer lines in NGC 5548 as reported by Dibai et al. (1968) were somewhat asymmetric, whereas those reported by Anderson (1970) are smooth and symmetric. We present profiles which are strongly asymmetric, resembling those of Dibai et al. Evidently electron scattering is not the sole principal broadening agent and we must deal with velocities ∼ 2500 km s−1 in a very small volume.

The transient nature of the P-Cygni type profiles in the Balmer lines of NGC 4151 has previously been noted (Cromwell and Weymann, 1970). These lines have since disappeared, at the resolution available to us, in a time of 3 months. A model in which frequent outbursts of shells or filaments produce transient features in the Balmer lines, while the accumulated material from past outbursts produces the relatively stable HeI λ 3889 feature, seems the most plausible.

I would like to present some new data concerning the Seyfert type galaxies Markarian 9, 10 and 42 (Khachikian, 1968; Arp et al., 1968; Khachikian and Weedman, 1969).

Current infrared observations of Seyfert galaxies, QSOs, and compact galaxies in the lists of Markarian and Zwicky have been reviewed. The bright Seyfert galaxies generally show similar infrared excesses at the longer wavelengths accessible from the ground. Only NGC 1068 has been observed, by F. J. Low, in the 100μ region; if the spectral distributions of all Seyfert galaxies are similar to that of NGC 1068, the intrinsic luminosities vary from 1 to 100 × 1044 erg s−1. Measurements by Kleinmann and Low, Gillett and Stein, Pacholczyk, and Penston and Neugebauer at 10 and 2μ apparently confirm variability of NGC 1068 and NGC 4151 on a time scale too short to allow the infrared radiation to come predominantly from dust shells.

The published infrared observations of QSOs have been limited to wavelengths shorter than 3.5μ except for 3C 273. The energy distributions either show a power law fall-off, a flat spectrum, or a combination of these two. Those four QSOs which show large variability all have steep power law spectra. If one accepts that the distance of QSOs are cosmological, the extrapolated luminosity at 2μ of several QSOs exceeds that of 3C 273. The integrated luminosity of 3C 273 depends critically on the spectrum in the unobserved 10–1000μ region, but is probably in the range 1047 to 1048 erg s−1.

The infrared observations of the compact Markarian and Zwicky objects show a correlation between the infrared excess and the broad optical emission lines. Presumably the infrared can be used to differentiate between the stellar and non-thermal components of the radiation from these objects.

The polarized optical and centimetric fluxes from BL Lac have their maxima at position angles which are roughly orthogonal. A similar tendency is found in other QSOs. If these fluxes are of synchrotron radiation then the magnetic fields associated with the optical and centimetric radiation are likely to be highly inclined with respect to each other. The implications of this are discussed.

This paper reports (1) a possible 5.1 yr period in the optical variations of the nucleus of NGC 4151; and (2) variations with a time-scale of a few days in the 2.2 micron flux density of NGC 1068, implying that the size of the infrared emitting region is not larger than a few times 1015 cm.

Light fluctuations have been found in all 22 QSOs studied by measurement of plates from the Harvard collection, which cover the last eighty years. The conclusions of this study are: (i) There appear to be at least three general classes of variation: (a) erratic, small-amplitude variations, (b) erratic, large-amplitude variations, and (c) slow quasi-periodic variations, e.g. as in 3C 273; (ii) No significant differences were detected between the rates of rise and decline of luminosity; (iii) Definite secular trends over at least 50 years were found in 5 QSOs; (iv) No simple clearcut periods greater than one year have been found; (v) There may be a trend of decreasing amplitude of fluctuations in apparent magnitude with increasing luminosity.

The fluctuations in optical brightness of the quasi-stellar object 3C 273 have been investigated to determine whether the suggested periodicity of ∼ 10 yr is supported by the observational data extending over 80 yr. New methods of obtaining information from the power spectrum have been used, and moments and trends have also been investigated. No statistically-supportable evidence has been found in the power spectrum for such a non-random variation. The moments and trends are consistent with random fluctuations. If the observed fluctuations are of shot-noise character, due to random outbursts of light, the individual pulses must occur at the rate of 15 ± 5 per year and have an average effective length of 3.2 ± 1 yr. These conclusions were verified by computer-generation and power-spectrum analysis of such random signals. Thus any periodic variation in the brightness of 3C 273, if present, is completely obscured by random fluctuations. The power spectrum, moments, and trend are all consistent with random but long-lasting outbursts of light.

Many people have attacked the problem of synthesizing the stellar population of the galaxies. We have performed such a synthesis, by using only the intensities of absorption lines in the nuclei of galaxies. It is then possible to obtain a synthesized continuous spectrum even if there are several possible solutions for the stellar composition, and the computed continuum does not vary much with the assumed model of stellar population.

The method is to fit the equivalent widths of the absorption lines using different stellar compositions. In order to avoid any instrumental effect, we have observed different lines and bands from 3500 to 8500 å in stars of various well-known stellar types and luminosity classes, under the same conditions as the galaxies.

We have applied this method to some ‘ordinary’ nuclei and to some Seyfert ones. As an example, we show the results for M81 and for NGC 1068.

Compact radio stars are associated with both galaxies and quasi-stellar objects; and there appears to be no way to distinguish between the radio galaxies and the quasi-stellar radio sources from their radio properties alone.

The compact radio sources are opaque at the longer radio wavelengths and have spectra that are either peaked or complex. They have a complex brightness distribution and often contain components less than 0.001 arc sec in size.

Many of the compact sources show large intensity variations and in NGC 1275 there is evidence for a change in the angular size during one year.

From 1965 to 1967 radio link interferometers were operated between Jodrell Bank and Malvern, at wavelengths of 21, 11, and 6 cm. Preliminary results were published by Adgie et al. (1965), Barber et al. (1966), Palmer et al. (1967) and Miley et al. (1967). The full analysis of these data has now been completed. Donaldson et al. (1969) report that six sources were unresolved, and they set size limits in the range 0.1 to 0.01 arc sec. Seven sources were found to contain unresolved components, and similar but less complete data were obtained on 33 other sources. Four sources (3C 119, 138, 147, and 237) were shown to have double or more complex structures. (Donaldson and Smith, 1970; Donaldson et al., 1970). The cores of 3C 274 and four other sources were shown to have elongations in the range 0.3 to 0.03 arc sec. One of these is 3C 287, and when the data on this source are combined with those of Clark et al. (1968) at 1660 MHz it appears that this source is a double of separation 0.08 arc sec in position angle 025°. This differs from the interpretation given by Clark et al. Some new data were also obtained on the well known double sources 3C 405 and 1938-15.

The statistics on the angular structures of quasars have been more than doubled. Quasars are discussed from both morphological and statistical viewpoints and the angular diameter-redshift relation has been confirmed.

Ten percent of the intrinsically bright elliptical galaxies contain compact radio sources (angular size < 3 arc sec) with radio luminosity ∼ 1040 erg s−1. The presence of a compact source is correlated with the presence of extended radio emission and with the presence of optical emission lines.

Results of a three-year investigation into the variability of 55 Parkes sources at 13 cm are presented. Thirty-six of the sources comprise a complete sample of QSS with fluxes exceeding 2 flux units. The remaining sources include most other known or likely variables stronger than 2 flux units. The relationship between spectra and variability in QSS is investigated and it is confirmed that variables generally have flat low frequency spectra. A possible relationship between redshift and specific types of intensity variations is considered. Limits on the secular change in the intensity of non-variable QSS are set and are generally found to be ± 1.5% p.a. at 13 cm. Results for the remaining 19 sources are discussed and some preliminary findings of an extension patrol to include weaker sources in the range 1-2 flux units are given.

Observations of the quasars 3C 273 and 3C 279 at 8 mm were begun in 1967 with the 22-m radio telescope of the Crimean Astrophysical Observatory of the Academy of Sciences of the USSR and have been continued subsequently (V. A. Efanov et al., 1968, 1969, 1970a, 1970b).