P. Andreani

Quasar Clustering: Evidence for an Increase with Redshift and Implications for the Nature of Active Galactic Nuclei

The evolution of quasar clustering is investigated with a new sample of 388 quasars with 0.3 0.0 are excluded at a 0.3% probability level, compared with ~ 0.8 found for galaxies. The observed clustering properties appear qualitatively consistent with a scenario of Ω = 1 cold dark matter in which (1) the difference between the quasar and the galaxy clustering can be explained as a difference in the effective bias and redshift distributions and (2) the quasars, with a lifetime of t ~ 108 yr, sparsely sample halos of mass greater than Mmin ~ 1012-1013 h-1 M☉. We also discuss the possibility that the observed change in the quasar clustering is due to an increase in the fraction of early-type galaxies as quasar hosts at high z.

The Enhancement and Decrement of the Sunyaev-Zeldovich Effect toward the ROSAT Cluster RX J0658–5557*

We report simultaneous observations of the X-ray cluster RX J0658-5557 at 1.2 and 2 mm made with a double-channel photometer on the Swedish ESO Submillimeter Telescope (SEST) in search of Sunyaev-Zeldovich (SZ) effect. The SZ data were analyzed using the relativistically correct expression for the Comptonization, and we find (2.60?0.79)?10?4 from the detected decrement, which is consistent with that computed using the X-ray (ROSAT and ASCA) observations. The uncertainty includes contributions from statistical uncertainties in the detection, systematics, and calibration. The 1.2 mm channel data alone give rise to a larger Comptonization parameter; this result is discussed in terms of contamination from foreground sources and/or dust in the cluster or from a possible systematic effect. We then make use of a combined analysis of the ROSAT and ASCA X-ray satellite observations to determine an isothermal model for the SZ surface brightness. Since the cluster is asymmetrical and probably in a merging process, models are only approximate. The associated uncertainty can, however, be estimated by exploring a set of alternative models. We then find a factor of 1.3 for the global uncertainty on the Comptonization parameter. Combining the SZ and the X-ray measurements, we determine a value for the Hubble constant. The 2 mm data are consistent with H0(q0=?)=53+38?28 km s-1 Mpc-1, where the uncertainty is dominated by the uncertainty in the models of the X-ray plasma halo.

Millimetric properties of IRAS galaxies — III. Luminosity functions, sub-mm counts and contributions to the sky background

We exploit observations at 1.25 mm with the ESO-SEST telescope of a southern galaxy sample, selected from the IRAS PSC and complete to

Diffuse galactic emission at millimetric wavelengths

S_{60}=2 Jy

THE VARIANCE OF QUASAR COUNTS IN CELLS

, to derive the FIR and mm luminosity functions and the conditional probability distributions of FIR and mm luminosity of galaxies. The reliability of these estimates is ensured by the good observed correlation of the far-infrared and mm emissions. This detailed knowledge of the millimetric properties of galaxies is used to simulate the extragalactic sub-mm sky (background intensity, small-scale anisotropy signals, and discrete source statistics) -- that will be investigated soon by a variety of ground-based and space observatories. We find, in particular, that the recent tentative detection of a sub-mm background would require, if confirmed, strong evolution with cosmic time of the galaxy long-wavelength emissivity. We finally emphasize the difficulty to test such evolution through observations from currently available millimetric sites on ground.

Looking for the S-Z Effect towards Distant ROSAT Clusters of Galaxies

Millimetric continuum observations of the Galactic disk at b about -8 deg and l about 290-310 deg has been achieved during the Italian 1987-1988 scientific expedition in Antarctica. Emission was detected from few southern clouds (the Chamaeleon region and a cirrus cloud), and their energy distributions reveal an excess in the long wavelength range. This fact is interpreted as being due to the presence of a cold component of the interstellar material coexisting with the warm dust responsible for the emission detected by IRAS. Then, a multiple nature of the interstellar dust is suggested also in regions far from the Galactic bulge. 45 refs.

The Evolution of the Clustering of QSOs

{}From three quasar samples with a total of 1038 objects in the redshift range

Looking for the Sunyaev-Zeldovich Effect toward Distant [ITAL]ROSAT[/ITAL] Clusters of Galaxies

1.0 \div 2.2

Cold dust around high-redshift quasars

we measure the variance

Submillimetre observations of galaxies – I. First results

\sigma^2