In this paper, we summarize the results of an analysis of faint galaxy counts presented in Guiderdoni and Rocca-Volmerange (1989). We choose to restrict our analysis here to the examination of pure luminosity evolution.

The optical brightness of the sky due to galaxies is determined up to 15.7 Zwicky magnitude and to B = 15m.

A new catalogue of faint galaxies on a 3 deg2 area near the North Galactic Pole (NGP), complete to J =24.5 and F =23.5, has been obtained from nine Canada France Hawaii Telescope prime focus plates. The angular correlation function has been measured for the first time to separations ~1°. Preliminary results indicate a power law slope of ≈ −0.8 at small separations and no sharp break for θ ≤ 1°. We also find some evidence that the power law slope flattens to fainter limiting magnitudes.

During 1987 and 1988, we obtained 12 long-exposure Schmidt plates of the cluster Abell-426 at the Konkoly Observatory. The pictures were digitized with a microdensitometer and added with a computer. The resulting blue images clearly show extended envelopes around the bright cluster members.

The infrared emission in galaxies is strongly connected to star burst processes, while emission from the intergalactic medium results mainly from dust heated by other luminosity sources. The Virgo cluster provides an extensive region in which the properties of such infrared emission can be studied. Galaxies in the Virgo cluster with dust temperatures of 40 K and masses of dust as small as about 5 × 104M⊙ are detectable at the limit of the IRAS survey (Soifer et al., 1987). The IRAS observations of 196 optically selected galaxies in the Virgo cluster have been studied by Helou et al. (Helou et al., 1988; see also Leggett et al., 1988).

The excess of higher redshift galaxies relative to the brightest member, found by several authors in poor, loose groups, is found to be present also in nearby, small groups identified by Geller and Huchra (1983) in the Center for Astrophysics Survey. This effect is explained as being due to the presence of diffuse intragroup dust together with an early evolutionary stage of nearby galaxy groups. An expected negative correlation between color excesses of galaxies and the velocity relative to the brightest member is found to be highly significant for both B-V and U-B colors. The optical depth produced by dust in groups turns out to be on the order of one, with a density of about 10−29 g/cm3.

NGC 1399, the central galaxy of the Fornax cluster, is known to have an overabundance of globular clusters (Hanes and Harris, 1986). In order to determine the luminosity function of these globular clusters, two fields near NGC 1399 were observed in the B, V, and R band. One field was chosen near the center of NGC 1399 and the second field 20′ east of the galaxy center. The second field is supposed to contain no globular clusters and is used for comparison. Both fields were reduced with DAOPHOT (Stetson, 1987) to determine the number-magnitude relation for all detected objects (see Figure 1). The differential number counts give log N (m) = 0.84 mB for the comparison field while the differential number counts for the central field (background galaxies and globular clusters) cannot be described by this simple law. Figure 2 shows the number-magnitude relation of the excess objects in the central field (difference between all counts in the central and in the comparison field). The differential number counts N (m) of the excess objects can be represented by the superposition of three populations, each following approximately a Gaussian distribution. The population with the brightest peak luminosity (mB = 22.1 mag) is due to a galaxy cluster with an estimated redshift z = 0.3–0.4. Figure 1.

The differential number counts of the central field (upper line) and the comparison field (lower line) are displayed for the band until 0.5 mag short of the limiting magnitude. The differential number counts of the comparison field can be described by a simple exponential law; this function is displayed as a dotted line. The differential number counts of the central field cannot be approximated by a simple exponential function.

The difference among all detected objects between both fields (Ncent(m) - Ncomp(m)) is shown for the B band. The excess objects in the central field can be represented by the superposition of three populations. This three-component Gaussian model is indicated by the dotted line. The most abundant population (N > 250) with peak luminosity mB = 24.8 mag is identified with globular clusters belonging to NGC 1399.

The vacuum ultraviolet (λeff = 156 nm and δλ ≅ 30 nm) observation around the Virgo Cluster region (l = 280°–320° and b = 60°–80°) was performed by the GUV experiment, a rocket-borne two-dimensional imager. The diffuse background radiation in the high galactic latitude region was obtained after subtraction of the contributions from airglow, stars, and galaxies in the field of view. A comparison with HI 21 cm radio observations indicates a weak correlation of the diffuse ultraviolet (UV) background radiation with HI column density, suggesting a low scattering efficiency of the interstellar dust grains in the far-UV and the existence of the isotropic component in the diffuse background radiation.

We have investigated the galactic infrared background (GIRB) light that comes from the integrated emission of individual galaxies at different redshifts. By using (1) the galaxy M 82 infrared (IR) spectrum as a template spectrum of IR active galaxies and (2) the constraint given by the nucleosynthesis of the heavy elements in galaxies, we have derived the IR spectrum of the diffuse light that comes from the galaxies at different redshifts following the method by Stecker, Puget, and Fazio (1977). The observations by Matsumoto et al. (1988) impose severe constraints on the possible scenarios for the birth and evolution of the galaxies. Observations by the COBE satellite are expected to settle some important issues of this problem.

The sky survey performed by the IRAS satellite provides a very homogeneous and almost complete view of the sky at infrared wavelengths. Suitable methods from multivariate statistics and decision theory are employed to extract the extragalactic background included in the IRAS Point Source Catalog. The resulting map comprehensively represents the distribution of extragalactic objects on the sky. The various selections may be used to assess large-scale structure in the distribution of galaxies and the total infrared background due to galaxies, to follow such structures closer to the Galactic Plane than is possible with optical data and to address cosmological questions (e.g., Harmon, Lahav, and Mauers 1987). These investigations are to be extended to the more sensitive Co-Added Catalog.

The possible presence of general extragalactic extinction has been studied by many authors. Extragalactic dust can be associated with a pregalactic star population and/or it can be ejected by galaxies during their evolution.

We propose that photons produced by decaying particles may account for the recently observed isotropic infrared background (IRB) between 1 and 5 μm. We find that for decaying particle masses mx between 5 and 18 keV, lifetime τd between 2 and 7 × 1010 s, and photon branching ratio Bγ between 4 and 9 × 10−4, the observed spectrum of decay photons is consistent with the observed spectrum of the IRB. The same parameters can explain the submillimeter background.

We present moderate to high signal-to-noise high-resolution (R ≈ 150,000–170,000) optical spectra toward ζ Oph. Gaussian fits to our data indicate a value of the line-width parameter b, of b = 1.4 ± 0.2 km s−1, along this line of sight. When CN is used as an indirect probe of the cosmic microwave background (CMB) temperature, the line profile is used to determine saturation corrections in the line. This affects column density calculations, which are reflected in the excitation temperature. Current measurements of the b-value along this line of sight range from 0.88 ± 0.02 km s−1 (Crane et al. 1986) to 1.3 ± 0.1 km s−1 (Hegyi, Traub, and Carleton 1972). The extreme range of these b-values yield saturation corrections to the CMB temperature that differ by 0.05 K, which is equal to the quoted precision of current measurements. Preliminary analysis of observations toward HD 29647 indicate that TCMB = 2.70 ± 0.14 K at 2.64 mm toward this line of sight.

We present very high signal-to-noise observations of the (1,0) and (0,0) vibrational bands of interstellar CN near 3580 and 3874 Å toward HD 21483. Corrected for saturation with a derived b-value of 1.29±0.05 km s-1, these CN line strengths yield excitation temperatures of 2.83±0.09 and 2.76±0.07 K for the J=1-2 and J=0-1 rotational transitions at 1.32 and 2.64 mm. In the absence of local CN excitation, these values represent the brightness temperature of the cosmic microwave background (CMB) radiation at these wavelengths. Millimeter observations have revealed no CN emission at 2.64 mm toward HD 21483 and allow us to set a 2σ upper limit of 0.11 K on the contribution of local processes to the J=0-1 excitation. Considering this limit and the lesser likelihood of local J=1-2 excitation, our observations indicate a CMB temperature of 2.83±0.09 K at 1.32 mm.

Recent observations (Matsumoto et al., 1988) indicate that at submillimeter wavelengths the spectrum of the cosmic background radiation (CBR) deviates from that of Planckian blackbody with a temperature T0R = 2.76 K. The relative excess of the flux ζ(v) = [F(v) – F0(v)] / F0(v) (where F(v) and F0(v) are the registered flux and the flux of the blackbody radiation at the frequency of the observations) are 0.6 at a frequency v1 = 380 GHz (λ = 709 μm) and 3.4 at a frequency v2 = 624 GHz (λ = 481 μm).

The study of the anisotropies of the submillimeter relict radiation (RR) can provide important arguments to select among different theoretical scenarios (Panek and Rudak 1988). However, interstellar dust (ISD) emission is present in this spectral region and its patchy distribution can heavily contaminate anisotropy measurements. For example, the most sensitive measurement of CBR anisotropies has been reported so far in a broad band around 1 mm (Melchiorri et al. 1981): the detection of anisotropy is statistically very significant, but its cosmological origin is questionable.

Deep observations of the cosmic microwave background (CMB) have been made at 10 GHz with beamwidths of 5° and 8° using a triple-beam technique, which greatly reduces atmospheric effects. Significant signals are detected with an rms of ΔT/T ~ 4×10−5. These signals could be intrinsic to the CMB and are providing fundamental information about galaxy formation in the early universe. A component of this 10 GHz emission may be coming from galactic synchrotron features. This galactic contribution will be elucidated in forthcoming 15 and 30 GHz observations.

The motion of the earth with respect to the distant matter frame produces a spectral distortion in the observed background radiation given by 1

The second-order approximation in β gives (de Bernardis et al., 1989) 2 where α≅(dlnI/dln v) = (v/I)(dI/dv). The first term in cosθ of equation (2) is the usual dipole anisotropy, the second constant term is the equivalent of the transverse Doppler effect in special relativity, and the third term is the quadrupole anisotropy. It is interesting to note that the quadrupole term is zero in the Rayleigh-Jeans region of the blackbody spectrum: Q ≈ 1/2(3–α)(2–α)β2cos2θ.

The Nagoya-Berkeley experiment has revealed a substantial excess over the blackbody radiation in the submillimetre part of wavelengths. Its origin is unknown. The concept of high-redshift cosmological dust (e.g., Hayakawa et al., 1987), though not without problems, remains one of the simplest explanations. It is clear that other types of observations will be necessary to identify the source of the excess. Needless to say, searches for cosmic background radiation (CBR) intensity fluctuations on fine angular scales in the submillimetre region are especially desired.

Matsumoto et al. (1988) have reported a significant distortion in the spectrum of microwave background radiation in the submillimetre waveband 400-700 μ. This follows a rocket experiment by a team from Nagoya and Berkeley in February, 1987. This experiment has resulted in a series of papers which have attempted to interpret this excess (see Carr, 1988). This result may force us to revise the process of universe recombination and/or to resort to nonequilibrium processes. The distortion of the cosmic microwave background radiation (CMB) from Planck spectrum may necessarily arise because of the production of energetic quanta in the process of recombination which lead to retarding former and distortion of CMB both in the Wein region and the Rayleigh-Jeans region (Zeldovich, Kurt, and Sunyaev, 1969; Lumbarskii and Sunyaev, 1983).