In order to extend radio source counts to lower flux density, we have used the VLA to survey a small region of sky at 4.885 GHz (6 cm) to a limiting flux density of 50 μJy. Details of this deep survey are given in the paper by Kellermann et al. (these proceedings). In addition, we have observed 10 other nearby fields to a limiting flux density of 350 μJy in order to provide better statistics on sources of intermediate flux density.

This paper describes the first results of systematic near IR photometry of radio galaxies in the Leiden Berkeley Deep Survey. The LBDS contains ∼ 400 radio sources with S1.4 GHz ≥ 0.22 mJy (for details see van der Laan et al., this symposium), 50% of which have reliable optical identifications on deep multicolor KPNO 4m plates, being mainly faint blue radio galaxies (Windhorst et al., 1982). The aim of the present IR photometry program is to study their IR properties and to obtain clues as to the nature of these faint blue radio galaxies, which may be either ellipticals, possibly with recent star formation, or spirals with exceptionally high radio power. The additional optical-IR color baseline will help to solve these questions.

This paper is concerned with the distant radio galaxies in a sample of bright sources selected at 178 MHz by Laing, Riley & Longair (1982). This sample is 96% complete for sources with θ < 10′ and the bias of the 3CR catalogue against sources of large angular size has also been reduced. Deep optical searches have located many candidate identifications, but the probability of a chance coincidence with an unrelated object is appreciable, especially in the faintest cases, unless the area to be searched is small. We have therefore mapped the sources with candidate identifications having V > 20, using the VLA at a wavelength of 6 cm (Laing, Owen & Puschell, in preparation), in order to search for radio cores. We have so far located cores in 16/23 sources and set 5σ upper limits of 0.6 mJy for the remainder. None of the cores had been detected previously. In all cases, the cores coincide with optical objects, although one source (3C 340) had been misidentified. Several ambiguities have now been resolved.

Although claims are often made that photometric surveys of faint field galaxies reveal evidence for evolution over recent epochs (z<0.6), it has not yet been possible to select a single evolutionary model from comparisons with the data. Magnitude counts are sensitive to evolution but the data is well-mixed in distance because of the width of the luminosity function (LF). Colours can narrow the possibilities but the effects of redshift and morphology can only be separated using many passbands.

We have recently completed a photometric study of fourteen rich clusters of galaxies in the redshift range 0.18≤z≤0.39. The data are based on JF photographic photometry of each field. We report on the analysis of the cluster galaxy colour distributions; in particular we find that all the clusters in our sample with z ≳ 0.26 contain an excess number of blue galaxies (i.e., show the Butcher-Oemler effect). The blue excess, which was measured in terms of the ratio of the fraction of blue galaxies observed to that expected on the basis of Dressler's (1980) [morphological mix, local projected galaxy density]-correlations, ranges from 2 to ∼5. The highest value of 4.8 found in the cluster C10024+1654 (z=0.39), confirms Butcher and Oemler's (1978) observations of this cluster.

The apparent colors in a flux-complete sample of galaxies depend on the redshifts and the spectral types in the sample. These in turn depend on both luminosity evolution and evolution of the shapes of the spectra. Thus in principle a great deal about the evolution of galaxies can be learned from complete multicolor surveys, especially now that large samples can be routinely generated by automatic machine measurement. The following will review what has been learned from recent work.

Butcher and Oemler have reported that many clusters of galaxies at high redshift have enhanced populations of blue galaxies when compared to nearby clusters of similar type. Since this claim is based on broad-band colors alone, it is essential to obtain spectra of these blue objects to determine if they are actually cluster members. These spectra can also be used to provide a rough morphological classification of these objects that are too distant for detailed imaging with ground-based telescopes.

As part of a three year program to study the evolution of galaxies, quasars, and radio sources (in collaborations with R. Kron and R. Windhorst), we will use over 30 nights on the KPNO 4-m CCD Cryogenic Camera System, in the multi-aperture mode, to measure the redshifts of several hundred very faint objects. These will be selected from four fields (SA68 00h+15; Lynx 08h+45; SA57 13h+30; Herc 17h+50); for each we possess 4-m plates in four bandpasses (limits: U≃23, B≃24, V≃23, I≃21) as well as Westerbork interferometer maps to 1 mJy at 21cm (a 50cm survey is in progress). Galaxies are selected randomly by their apparent red magnitudes as measured with a PDS; quasar candidates to B≈22.5 by stellar objects which lie apart from Galactic stars in the multi-color diagram; and radio sources by their positional coincidence with optical images (∼50% of the 300 radio sources are identified). To date, 10 nights have produced spectra of ∼250 field galaxies, ∼20 radio sources, and ∼40 quasar candidates.

We have observed 3 moderate redshift clusters using a combination of 7 intermediate band filters and 2 CCDs in order to derive photometric information for cluster galaxies from 400 nm to 900 nm. Preliminary results are presented for 2 clusters: Abell 1942 (z=0.224) and Abell 1525 (z=0.259) from 580 nm to 860 nm. The CCD photometry reaches a limit equivalent to RF=21 mag with a precision of better than 0.1 mag. The galaxy colours derived from the intermediate band measurements are generally consistent with those expected at the appropriate redshift. However, in Abell 1525, and to a lesser extent in Abell 1942, a large proportion of cluster members have far red (720–860 nm) colours redder than expected. Many of these galaxies have blue photographic BJ-RF colours. A possible explanation for the anomalous CCD colours is that these galaxies possess a strong emission line component which enters the far red filter at z=0.25.

Population III has been invoked to explain the missing mass in the haloes of galaxies, the first heavy elements in our Galaxy and even to explain the whole microwave background. However there are alternative explanations for each of these phenomena. The most compelling evidence for the existence of a pregalactic generation of objects is the observed distortion of the microwave background in the millimetre range, which can be explained as radiation from Population III objects absorbed and re-emitted by dust grains. If the distortion is confirmed, we can probably conclude that the density fluctuations in the early universe were isothermal and that no neutrino can have a mass in the astrophysically interesting range 1–100 eV.

I consider experiments to confirm the substantial deviations from a Planck curve in the Woody and Richards spectrum of the microwave background, and search for conducting needles in our galaxy. Spectral deviations and needle-shaped grains are expected for a cold Big Bang, but are not required by a hot Big Bang.

If primordial fluctuations were isothermal their amplitude at recombination would be non-linear on scales Mo ≃ 106÷9 M⊙. Since the Jeans mass after recombination is MJo ≃ 8 × 105 Ω−1/2 M⊙ the clouds of mass Mo would be able to form the first generation of compact objects, the so-called Population III. These clouds would acquire angular momentum via tidal interactions with their neighbours. The importance of rotation can be conveniently characterised by the spin parameter λ = Vrotation/Vfree-fall and tidal interactions lead to a spin λo = 0.07 ± 0.03. As the cloud collapses λ increases as r−1/2. Any fragment forming in a rotating cloud would have the same spin λ as the whole cloud. It could therefore collapse only by ≃ λo2 in radius before centrifugal forces intervened, thus leaving a large geometrical cross-section for coalescence to be important. At radii r ≲ λo8/5 (Mo/MJo)2/15 ro the coalescence time is shorter than the free-fall time and no fragmentation is possible below this radius. In the primordial clouds two major factors prevent fragmentation at larger radii. First, the background radiation is still ‘hot’ and the trapping of it would prevent fragmentation until the whole cloud has collapsed to a radius 10−2 x−2/3 ro. Here x = 10−2(M/107 M⊙)1/3 is the ionization fraction given by the balance between gravitational contraction and recombination cooling. Furthermore, any small density fluctuation would lead to fragmentation only after the paternal cloud had collapsed by a factor (δ/5)2/3 in radius. For these reasons fragmentation is unlikely until centrifugal forces halt the collapse and a disk forms. The disk will be initially at T ≃ 104K but after a small fraction of H2 forms it will cool to T3 ≃ T/103K ≃ 1 and the final fragments mass could be as low as ≃ 0.2(λo/0.07)4 T32(MJo/Mo)1/3 M⊙.

One of the greatest mysteries of nature is the absence of any trace of the present structure of the nearby universe in its relict 3K emission.

If we live in an evolving world (which evolves from extremely smooth to extremely structural), our radio telescopes should see observable temperature variations of 3K in practically any world model.

The VLA has been used at 4.9 GHz to observe a small region of sky in order to extend the radio source count to low flux density (Fomalont et al., these proceedings) and to look for small scale fluctuations in the 2.7 K cosmic microwave background radiation.

Considerable astronomical interest attaches to sensitive measurements of temperature fluctuations of the microwave background on scales of a few arcmins to a few degrees. We describe here the first in a series of experiments being carried out at Jodrell Bank which are aimed at providing reliable and repeatable information on these angular scales. The first experiment used the MK II 25m dish at λ6 cm and covered scales from 10 arcmin (the beamwidth) to 60 arcmin (twice the beamthrow). At this relatively long wavelength, the atmosphere has negligible effect on the observations and day to day repeatability consistent with receiver noise alone was obtained. The observations were made in wagging mode near the North Celestial Pole (NCP) so that the two beams alternately traced out a reference circle on the sky, radius 30 arcmin, over the course of 24 hours. The NCP field was chosen since a high sensitivity discrete source survey (Pauliny-Toth et al. 1978) was already available covering the area. This meant that antenna temperatures around the reference circle could be corrected for any source induced effects ≳0.4 mK. In addition control observations were made at positions 30 arcmin East and West of the central field, so that systematic effects due to interaction of telescope sidelobes with objects in the immediate telescope environment, could be monitored and removed.

Source counts which now extend to surface densities of ∼105 sources/sr make possible a direct evaluation of the radio source contribution to the small-scale fluctuations in the microwave background on scales larger than ∼10′, at wavelengths cm. Comprehensive radio spectral data permit a straightforward and largely model-independent extrapolation of the N(S) relation to shorter wavelengths. On the other hand, Peacock and Gull (1981, hereafter PG) have constructed a set of models which incorporate a wealth of additional data, such as local luminosity functions, luminosity/redshift distributions, luminosity-spectral index correlations; they can therefore be exploited to optimize the extrapolations both to higher frequencies and to fainter flux densities. Only one of these models, however, namely No. 4, is consistent with the recent P(D) results (Wall et al. 1982; Ledden et al. 1980) which provide information on the areal density of sources at s~1mJy; therefore, in the following we shall focus on it.

Quantum fluctuations of the cosmic background have been measured in the 900 to 2000 micron range (H.P.B.W.) by means of a balloon-borne correlator operating between 5 and 150 Hz. Preliminary results indicate an upper limit √<dP2> ≤ 2.1 × 10−17 watt/(cm2 srad Hz)1/2, corresponding to the noise of a blackbody at a temperature T ≤ 3.1 K at 1σ.

We report preliminary results relative to a balloon-borne search for the large-scale anisotropy carried out in 1980 by means of two far infrared photometers centered at 400 and 1100 microns. While these results are consistent with those obtained in an earlier flight, the second, shorter wavelength channel included in the 1980 work provides interesting insights into the influence of galactic dust on such far infrared observations.

Scientific interest in large-scale anisotropy measurements is now focused on intrinsic effects, which could tell us much about the early Universe. Current experimental precision of better than 10−4 K begins to probe for interesting physical processes. However, at these levels of precision systematic effects and foreground sources present serious difficulties. Some recent results from balloon flights of a maser radiometer (λ 1.2 cm) and a cooled mixer (λ 3 mm) are discussed and interpreted. The dipole effect gives a velocity for the Local Group in the general direction of the Virgo cluster. The Earth's motion is clearly seen. There is no quadrupole detected at a level of ΔT/T ∼ 5 × 10−5.

The observed microwave background radiation is a sensitive tool for studying the fundamental features of the universe. A puzzling constancy on the celestial sphere of the temperature, T, of the equilibrium relic radiation coming to us from causally nonrelated regions of space-time points to the global spatial homogeneity and isotropy of the cosmological expansion. On the other hand, a small anisotropy of the relic background can tell a lot about the physics of the beginning of the universal expansion, where primordial cosmological perturbations, which later affect the relic isotropy, formed (see, e.g., [1,2] and other reviews on the early universe). We would like to emphasize another factor that forms mainly the large-scale structure of relic anisotropy: the spatial curvature of the background Friedmann Universe. In the light of the discovery of the large-scale anisotropy of the cosmic radiation [3–5], this problem becomes very important.