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COBE has provided preliminary results on the spectral distribution of both Cosmic Background Radiation (CBR) brightness and dipole anisotropy. We combine these data in order to compare COBRA results with those of COBE and to obtain more stringent upper limits to CBR spectral distortions. The possibility of having detected extragalactic diffuse lines is discussed.

The last few years have seen a large development of mm technology and ultra-sensitive detectors devoted to microwave astronomy and astrophysics. The possibility to deal with large numbers of these detectors assembled into multi--pixel imaging systems has greatly improved the performance of microwave observations, even from ground--based stations, especially combining the power of multi--band detectors with their new imaging capabilities. Hereafter, we will present the development of a multi--pixel solution devoted to Sunyaev--Zel'dovich observations from ground--based telescopes, that is going to be operated from the Millimetre and Infrared Testagrigia Observatory., 5 pages, 3 figures, to be published in th eProceedings of the 2K1BC Workshop, July 9-13, 2001 - Breuil-Cervinia

We describe a measurement of the angular power spectrum of anisotropies in the Cosmic Microwave Background (CMB) from 0.3 degrees to ~10 degrees from the North American test flight of the BOOMERANG experiment. BOOMERANG is a balloon-borne telescope with a bolometric receiver designed to map CMB anisotropies on a Long Duration Balloon flight. During a 6-hour test flight of a prototype system in 1997, we mapped > 200 square degrees at high galactic latitudes in two bands centered at 90 and 150 GHz with a resolution of 26 and 16.6 arcmin FWHM respectively. Analysis of the maps gives a power spectrum with a peak at angular scales of ~1 degree with an amplitude ~70 uK., 5 pages, 1 figure LaTeX, emulateapj.sty

We show how combined large-beam infra-red and radio observations toward the Virgo Cluster may be explained by assuming the existence of a large tepid halo surrounding the giant galaxy M87. Such a halo would be able to close the cluster gravitationally. If interpreted as being due to bremmstrahlung radiation by a tepid extended halo, it also explains the infra-red observations, and it has important implications for the physics of M87.

We analyse the spectral shape and possible spurious distortions of the Sunyaev-Zel'dovich effect, arising from the interaction of the cosmic background radiation with hot gases of rich clusters, in the millimetric region. We show that one can measure this effect with high accuracy with present-day infrared detectors, obtaining a larger amount of information than by using radio systems. In particular, one can accurately measure the temperature of the cosmic background radiation without the usual absolute calibration of the detector.

We analyze the anisotropies in the extragalactic infrared background and in the source counts in standard cosmology perturbed by large-scale, small-amplitude density fluctuations. The dipole anisotropy of the diffuse background is connected to the dipole of the cosmic background radiation and of the source counts, and a full consistency with a large (≃ 7%) anisotropy in the IRAS source counts is found to imply a low density (Ω0 ≃ 0.2) universe, contrary to a previous claim. We analyze also higher order harmonics. Using the IRAS Low-Resolution All-Sky Maps we obtain an upper limit of 0.17MJy/sr on the dipole of the 100 μm background and show that it is consistent with a source-count anisotropy of 7% only for a low intensity, I ≤ 1.2 M Jy/sr, of the background itself.

The observations of the Zel'dovich effect in galaxy clusters are reviewed. The failure to detect the effect at short wavelengths is interpreted as proof of the existence of intergalactic dust. Small and fast spinning grains can emit the power needed to compensate the decrease in temperature expected from the Zel'dovich effect.

The classical cosmological theories, based on the solution of field equations, have encountered a certain number of difficulties. To overcome these, cosmologists tend to consider new theories, especially for the early epochs of the Universe where general relativity is expected to fail.

The possibility of detecting diffuse sky radiation in the (250÷3000) μm range is discussed on the basis of recent measurements performed at the mountain observatory of Testa Grigia (3500 m a.s.l.) on the atmospheric emission and on the atmospheric noise. It is shown how, in many cases, the limits assigned by the residual atmospheric emission are well below the sensitivity of the available infra-red detectors; as a consequence some new experiments of background astronomy are suggested.

We measured the anisotropy of the cosmic background radiation at the angular scale of 2/sup 0/ in the millimetric wavelength region, in the course of the NASA-ESA ASSESS II Mission. We set upper limits on the anisotropy in several sky regions, the most stringent one being ..delta..T/T

Results of our wide beam radio observations of M87 are given here. Combined with the infrared observations of Virgo (Ceccarelli et al. 1982), we show that in order to explain both the radio and infrared observations, it is convenient to postulate an extended tepid (∼(+5) K ) halo, in addition to a hot (∼(+8) K ) halo surrounding M87. This tepid halo would be able to close the system gravitationally.

We have evaluated the accuracy in maintaining the differential modulation parallel to the horizon, which is required to reduce the atmospheric background below the detector noise in an infrared telescope operating under optimized conditions.

Results concerning zodiacal dust emission are reported from an IR sky survey experiment performed during a balloon flight on July 30, 1984 which explored five wavelength bands centered at 11, 19, 50, 108, and 225 microns. The dust density n decreases at a rate slower than r exp -1.3 with increasing heliocentric distance. The trend of n depends critically on the radial variation of the temperature which, in turn, depends on the chemical composition of the grains. The spatial distribution of the dust is in good agreement with that previously inferred from IR measurements. A comparison between IR and optical observations points out the uncertainties affecting the estimates of the dust density obtained with both methods. The emission spectrum of the dust is used to discriminate among the different species of grains, showing that the observations can be accounted for by an appropriate mixture of graphite and silicates. 18 references.