Counting the number of galaxies as a function of their apparent brightness is one of the fundamental cosmological tests, providing an important probe of both the geometry and evolutionary history of the Universe. CCD detectors have in recent years enabled astronomers to explore magnitude limits undreamed of a decade or so ago, and where important constraints can be placed on the allowable combinations of q0 and evolution. Recent work has shown that the B-band counts keep rising with a power-law distribution, with a fivefold excess in the number of galaxies at B = 26.5 over that expected from simple non-evolving models. Indeed, it has been suggested that the total numbers of galaxies already seen may be too high for a q0 = 0.5 universe, assuming there is a redshift cut-off in the galaxy distribution caused either by galaxies having strong Lyman limit systems or a low redshift of formation. As q0 = 0.5 is favoured by theoretical arguments, it is important to see if the behaviour of the counts at even fainter magnitudes can be reconciled with a high density universe. Most published counts are unreliable faintward of B ≈ 26, as the incompleteness corrections required become comparable in size to the data. We have now extended the counts to B ∼ 28, using a ∼ 24 hour CCD exposure taken on the 2.5 m Isaac Newton telescope (INT) on La Palma, together with a ∼ 10 hour exposure on a small part of this field taken using the 4.2 m William Herschel Telescope (WHT).

Rest-frame Strömgren colours are presented for a large number of galaxies in rich clusters between z = 0 and z = 1. Our observations confirm a strong, rest-frame, Butcher-Oemler effect where the fraction of blue galaxies increases from 20% at z < 0.4 to 80% at z = 0.9. After isolating the red objects in each cluster we have compared the mean colour of these old, non-star forming objects with SED models from the literature as a test for passive galaxy evolution in ellipticals. We find good agreement with single burst models which predict an epoch of galaxy formation from z = 2 to 5 (Rakos et al. 1988, 1991; Rakos & Schombert 1993). Although the results demonstrate a great deal of hope for modelling the fine details of colour evolution when our samples are extended into the near- and far-IR, there are reasons to believe that galaxies become, observationally, much more complicated beyond redshifts of 1. The rate of blue colour evolution between 0.6 and 0.9 suggests that by a redshift of 1.5 it will be impossible to tell the difference between galaxies which have completed a single burst at a formation redshift of 2 or ones which are undergoing constant star formation.

Clusters of galaxies are used to study large scale structure and evolution in the universe. The luminosity functions of clusters can be used to investigate their evolutionary effects while their spatial and angular correlation functions are a measure of large-scale clustering. There are, however, many problems with the traditional cluster catalogues that were derived by visual inspection of plate material. The widely used Abell catalogue (Abell 1958) has been shown to have significant problems in homogeneity and completeness (Postman et al. 1986).

We present the first results of cross-correlating the IRAS FSDB with the ROSAT All-Sky Survey. From the IRAS FSDB (∼ 750,000 entries) a sample of 10,317 IRAS galaxies has been extracted using the following selection criteria:

X-ray variability in the 0.1–2.4 keV ROSAT energy band with a doubling timescale of 800 s and a factor of 4 within a few hours has been detected in a 20 ksec pointing on the IRAS AGN 13224-3809. The optical spectrum indicates that IRAS 13224-3809 is a narrow-line Seyfert 1 galaxy with strong permitted Fe II emission, a member of the unusual I Zw 1 class objects. IRAS 13224-3809 appears to be one of the most rapidly variable AGN known so far. This is the first time that variability on a timescale smaller than 1000 s is reported at such high L (0.1–2.4 keV) = 3·1044erg · s−1 X-ray luminosity in Seyfert galaxies. It is also the first reported X-ray variability in I Zw 1 class objects. The δt = 800 s variation indicates that the X-rays come from a compact region of about 17 light minutes in size. Our results from the X-ray spectral analysis favour a scenario in which a hard X-ray source irradiates the accretion disk which reemits at soft X-ray energies. The absence of broad H I wings can be explained if only a part of the BLR, far from the centre, is observed and the bulk of the region, which emits the wings, is hidden. We want to draw attention to the fact that rapid X-ray variability could also be connected with the absence of broad H I lines in IRAS 13224-3809.

ROSAT All Sky Survey observations of IRAS galaxies have revealed up to now a number of (10) optically non-Seyfert galaxies with X-ray (0.1–2.4 keV) luminosities up to a few 1043erg · s−1 (Boller et al. 1992). The sources are brighter than previous detection limits of a few 1041erg · s−1 as found by Stocke et al. (1991) or Green, Anderson & Ward (1992) for Einstein sources. The optical classification is based on follow-up observations which indicate clearly the non-Seyfert (LINER and HII region-like galaxies) nature. Our investigations reveal that galaxies classified as non-Seyferts on the basis of optical spectroscopy may reach exceptionally high X-ray luminosities which are similar to that of Seyfert galaxies. On the basis of the present observational material we suppose a hidden low luminosity AGN in the centre of these objects as the source of energy production. The objects are of interest when evaluating starburst versus central activity.

The Press-Schechter formalism is used to derive the abundance of rich galaxy clusters in dependence on the cluster mass or the corresponding X-ray temperature of the hot gas confined in the cluster potential wells. We consider a characteristic double inflation spectrum in the standard CDM model leading to a hierarchical clustering scenario. Normalising the amplitude to the COBE-quadrupole, and supposing a biasing b ≈ 2, we get a reasonable fit both to the amplitude and the slope of the X-ray temperature function of Edge et al. (1990) and Henry & Arnaud (1991). In the considered model the cluster abundance changes strongly with redshift.

The nearby galaxy distribution suggests a remarkable structure in which large voids are delineated by dense walls of galaxies in a cell-like pattern. The nearby voids range in diameter from ∼ 10 to ∼ 50h−1 Mpc. Deeper surveys appear to be consistent with the nearby distribution and show no evidence of voids larger than ∼ 100h−1 ∗ Mpc. We might thus have reached the scale where the universe becomes homogeneous. The size of the largest inhomogeneities in the galaxy distribution is an important issue because it can put tight constraints on the theoretical models when confronted by the high degree of isotropy of the microwave background radiation.

Comparison of the various existing redshift surveys emphasizes the need for systematic redshift surveys over significant areas of the sky out to intermediate and large distances. Although deep pencil-beam surveys are best suited for probing a large number of voids and walls, understanding the nature of the intercepted peaks and valleys in terms of large-scale structure requires that the angular coverage of the surveys be larger than the galaxy auto-correlation length. If this condition is not satisfied, the size of the voids and the density contrast of the walls can be overestimated.

We present preliminary results of a galaxy redshift survey we are accomplishing as an ESO Key Project over about 40 square degrees in a region near the South Galactic Pole, to a limiting magnitude bJ = 19.4. Up to now ∼ 50% of the survey has been completed, providing about 2000 galaxy redshifts.

We report on the progress of the compilation and analysis of the Durham/UKST galaxy redshift survey. This survey will probe a large contiguous volume of space within a 1500 sq. deg. area of sky around the SGP. It will contain redshifts of ∼ 4000 galaxies of bJ < 17m providing detailed information about the structure of the Universe on large scales. Large features on scales of ∼ 100h−1 Mpc are clearly visible on examination of the completed section of the survey, although a statistical analysis of the survey by means of the two-point correlation function is close to zero on scales of r > 10h−1 Mpc.

The Muenster Redshift Project provides to date 0.9 million low-resolution redshifts obtained from automatic reductions of pairs of direct and low-dispersion objective prism Schmidt plates. Preliminary results obtained from subsamples of the survey are described.

Recent redshift surveys of the Nilson-, Zwicky-, and ESO-Uppsala galaxy catalogues revealed that the bright galaxies in these catalogues follow a spatial distribution where large empty regions are surrounded by sheet-like structures of galaxies and clusters (e.g. Giovanelli & Haynes 1991). From an observer's point of view, one may simply ask if the voids in the above-mentioned galaxy maps are real or if they reflect special observational selection effects, e.g. in surface brightness, integral magnitude or diameter. These catalogues contain many bright galaxies (MB ∼ M∗B), but only very few faint objects (MB ≥ M∗B + 3m). Older work on the distribution of intrinsically faint galaxies, like irregular dwarfs, claimed that the dwarfs follow the distribution which is outlined by the giant galaxies.

We present a new survey of emission line galaxies, performed with the ESO 1 m Schmidt telescope equipped with the 4° objective prism using IIIa-J photographic emulsion. The plates are digitized with the MAMA microdensitometer. A subsequent reduction of the block scans gives redshifts with a mean accuracy of 160 km/s−1, and spectrophotometric measurements of the intensity and equivalent widths of the principal emission lines. A brief discussion is given of the possible extension of quantitative reduction of slitless spectroscopy to archive plates and future large CCD array frames.

Accurate estimates of distances and peculiar velocities for galaxies may be derived with the help of multi-dimensional regression analysis using two or more distance indicators pk (corrected apparent sizes, luminosities, other distance-dependent quantities) and some calibrators q1 (velocity dispersions of the ellipticals or HI-line widths of the spirals, mean surface brightness, colours, other distance-independent quantities) together, cf. Georgiev (1992). Here an example is given for 349 spiral galaxies with axial ratio D/d > 1.4 from the sample of Fisher & Tully (1981). The p-values are the major axis and the blue magnitude and the q-values are the HI line width, type and axial ratio.

Over the past 17 years a large scale quasar monitoring programme has been underway at the Royal Observatory, Edinburgh, using COSMOS measures of a long sequence of plates from the UK 1.2 m Schmidt telescope in Australia. 3 or 4 plates were taken each year, and quasar candidates were selected solely on the basis of variability, with a minimum amplitude of 0.35 mag. over the 17 years of the survey. Of the 1000 or so quasars detected in this way, redshifts were available for about 300, which formed the sample to be investigated. Inspection of the light curves suggested a typical timescale of variation of around 5 to 10 years. To investigate the cause of variability, the timescales of subsamples were measured using the timevarying autocorrelation function (ACF).

The digital revolution in the evaluation of photographic plates and the introduction of automated quasar search techniques have drastically increased the number of known QSOs over the past decade. However, most of these QSOs are so faint that their use is limited to statistical studies. The bright end of the quasar population is still dominated by objects selected in other wavebands, such as radio, X-rays, or even infrared. We have started in 1990 a wide-angle objective-prism survey (the Hamburg/ESO Survey, HES) using the 1 m ESO Schmidt telescope (Reimers 1990). The survey is intended to cover 5000 deg2, of which about a third has been acquired up to now. The prime goal is to compile a large sample of bright (B < 17.5) QSOs suited for detailed follow-up studies, in particular for high-resolution spectroscopy. Other objectives are to search for gravitational lens candidates and to directly measure the local luminosity function of quasars. In each Schmidt field, a spectral and a direct plate are scanned with the PDS 1010G microdensitometer at Hamburg, followed by an automated candidate selection and subsequent follow-up spectroscopy with the ESO 1.52 m and 3.6 m telescopes. A novel feature in our survey is the use of an objective-prism with a dispersion of 450 å/mm at Hγ, yielding a seeing-limited spectral resolution of 10–20 å FWHM. A full documentation of the survey techniques is in preparation. First results include the discoveries of the second-brightest QSO in the south (Wisotzki et al. 1991), and of a bright double QSO at high redshift, probably a gravitational lens (Wisotzki et al. 1993). In this contribution I want to show how a wide-angle quasar survey like the HES can benefit from the high resolution of the survey spectra.

The Hamburg Quasar Survey is carrying out an objective-prism survey on Schmidt plates taken at the Spanish-German Astronomical Centre (DSAZ) on Calar Alto/Spain. We use a 1.7 deg objective-prism providing unwidened spectra with a dispersion of 1390 å/mm at Hγ on hypersensitized KODAK IIIa-J plates. The field size is 5.5 × 5.5 deg. For each field, two prism plates are taken to improve the recognition of faint spectra. A direct plate is taken to determine accurate positions, and to recognize overlaps and extended objects. The coverage of the extragalactic fields up to 1993 is given in Engels et al. (1993).

On the basis of the Second Byurakan Survey (SBS), we have produced a new complete sample of bright QSOs.

The observations were obtained using the 1.5, 3 and 4 degree objective prisms with the 40–52 inch Schmidt telescope at the Byurakan Observatory. The total sky coverage area of SBS is 1000 square degrees from R.A. 07h40m–17h15m and Dec. +49–+61.

In all, in SBS about 3000–1600 stellar objects have been selected, and about 1400 galaxies down to a limiting magnitude B ∼ 19.5.

290 QSO and 67 Sy galaxies are spectroscopically confirmed.

The estimate of surface density of SBS QSOs in the magnitude range 15.5 < B < 17.2 and redshift distribution of SBS QSOs and Sy galaxies are given.

We report first results of a photometric investigation of the optical long-term behaviour of a sample of quasars. Our study is based on the plate archive of the Tautenburg 134 cm Schmidt telescope which covers a time baseline of over 30 years.

Increasing the density of known quasars in wide fields is of great interest, especially in the frame of the search for a possible very-large-scale structuring of the Universe. We report here on the status of two photographic systematic surveys for quasar candidates that we are conducting.