The large scale clustering of radio sources

The observed two-point angular correlation function, w(theta), of mJy radio sources exhibits the puzzling feature of a power-law behaviour up to very large (almost 10 degrees) angular scales which cannot be accounted for in the standard hierarchical clustering scenario for any realistic redshift distribution of such sources. After having discarded the possibility that the signal can be explained by a high density local source population, we find no alternatives to assuming that - at variance with all the other extragalactic populations studied so far, and in particular with optically selected quasars - radio sources responsible for the large-scale clustering signal were increasingly less clustered with increasing look-back time, up to at least z=1. The data are accurately accounted for in terms of a bias function which decreases with increasing redshift, mirroring the evolution with cosmic time of the characteristic halo mass, M_{star}, entering the non linear regime. In the framework of the `concordance cosmology', the effective halo mass controlling the bias parameter is found to decrease from about 10^{15} M_{sun}/h at z=0 to the value appropriate for optically selected quasars, 10^{13} M_{sun}/h, at z=1.5. This suggests that, in the redshift range probed by the data, the clustering evolution of radio sources is ruled by the growth of large-scale structure, and that they are associated with the densest environments virializing at any cosmic epoch. The data provide only loose constraints on radio source clustering at z>1 so we cannot rule out the possibility that at these redshifts the clustering evolution of radio sources enters a different regime, perhaps similar to that found for optically selected quasars. The dependence of w(theta) on cosmological parameters is also discussed.Comment: 9 pages, 8 figures. Accepted for publication on MNRA

Star formation across cosmic time with radio surveys. The promise of the SKA

This lecture briefly reviews the major recent advances in radio astronomy made possible by ultra-deep surveys, reaching microJansky flux density levels. A giant step forward in many fields, including the study of the evolution of the cosmic star formation history is expected with the advent of the Square Kilometer Array (SKA).Comment: 28 pages, 3 figures, to be published in the Proceedings of the 3rd Cosmology School in Cracow, July 201

Impact of foregrounds on Cosmic Microwave Background maps

We discuss the possible impact of astrophysical foregrounds on three recent exciting results of Cosmic Microwave Background (CMB) experiments: the WMAP measurements of the temperature-polarization (TE) correlation power spectrum, the detection of CMB polarization fluctuations on degree scales by the DASI experiment, and the excess power on arcminute scales reported by the CBI and BIMA groups. A big contribution from the Galactic synchrotron emission to the TE power spectrum on large angular scales is indeed expected, in the lower frequency WMAP channels, based on current, albeit very uncertain, models; at higher frequencies the rapid decrease of the synchrotron signal may be, to some extent, compensated by polarized dust emission. Recent measurements of polarization properties of extragalactic radio sources at high radio frequency indicate that their contamination of the CMB polarization on degree scales at 30 GHz is substantially below the expected CMB E-mode amplitude. Adding the synchrotron contribution, we estimate that the overall foreground contamination of the signal detected by DASI may be significant but not dominant. The excess power on arc-min scales detected by the BIMA experiment may be due to galactic-scale Sunyaev-Zeldovich effects, if the proto-galactic gas is heated to its virial temperature and its cooling time is comparable to the Hubble time at the epoch of galaxy formation. A substantial contamination by radio sources of the signal reported by the CBI group on scales somewhat larger than BIMA's cannot be easily ruled out.Comment: 10 pages, 5 figures, to appear in proc. int. conf. "Thinking, Observing and Mining the Universe", Sorrento, Sept. 200