The role of relativistic jets in the heaviest and most active supermassive black holes at high redshift

In powerful radio-quiet active galactic nuclei (AGN), black holes heavier than one billion solar masses form at a redshift ~1.5-2. Supermassive black holes in jetted radio-loud AGN seems to form earlier, at a redshift close to 4. The ratio of active radio-loud to radio-quiet AGN hosting heavy black holes is therefore a rather a strong function of redshift. We report on some recent evidence supporting this conclusion, gathered from the Burst Alert Telescope (BAT, onboard Swift) and by the Large Area Telescope (LAT, onboard Fermi). We suggest that the more frequent occurrence of relativistic jets in the most massive black holes at high redshifts, compared to later times, could be due to the average black hole spin being greater in the distant past, or else to the jet helping a fast accretion rate (or some combination of the two scenarios). We emphasize that the large total accretion efficiency of rapidly spinning black holes inhibits a fast growth, unless a large fraction of the available gravitational energy of the accreted mass is not converted into radiation, but used to form and maintain a powerful jet.Comment: 6 pages, 3 figures, accepted for publication in MNRAS, main journa

Heavily obscured AGN in the local Universe

We present here a new powerful diagnostic plot to select heavily obscured AGN in the local universe by combining infrared (Spitzer, IRAS) and X-ray (XMM) information. On the basis of this plot, we selected a sample of X-ray obscured sources in the 2XMM catalogue and found seven newly discovered Compton-thick AGN candidates.Comment: 2 pages, 2 figures, To appear in refereed Proceedings of "X-ray Astronomy 2009: Present Status, Multi-Wavelength Approach and Future Perspectives", Bologna, Italy, September 7-11, 2009, AIP, eds. A. Comastri, M. Cappi, and L. Angelin

XMM-Newton observations of ULIRGs I: A Compton-thick AGN in IRAS19254-7245

We present the XMM-Newton observation of the merging system IRAS 19254-7245, also known as The Superantennae, whose southern nucleus is classified as a Seyfert 2 galaxy. The XMM-Newton data have allowed us to perform a detailed X-ray imaging and spectral analysis of this system. We clearly detect, for the first time in this system, a strong EW ~ 1.4 keV Fe emission line at 6.49+/-0.1 keV (rest-frame). The X-ray spectrum requires a soft thermal component (kT~0.9 keV; L(0.5-2) ~ 4E41 cgs), likely associated with the starburst, and a hard power-law continuum above 2 keV (observed L(2-10) ~ 4E42 cgs). We confirm the flatness of this latter component, already noted in previous ASCA data. This flatness, together with the detection of the strong Fe-Kalpha line and other broad band indicators, suggest the presence of a Compton-thick AGN with intrinsic luminosity > 1E44 cgs. We show that a Compton-thick model can perfectly reproduce the X-ray spectral properties of this object.Comment: 6 pages, 4 figures, Latex manuscript, Accepted for publication in Astronomy and Astrophysic

The Kormendy relation of massive elliptical galaxies at z~1.5. Evidence for size evolution ?

We present the morphological analysis based on HST-NIC2 (0.075 arcsec/pixel) images in the F160W filter of a sample of 9 massive field (> 10^{11} M_\odot) galaxies spectroscopically classified as early-types at 1.2<z<1.7. Our analysis shows that all of them are bulge dominated systems. In particular, 6 of them are well fitted by a de Vaucouleurs profile (n=4) suggesting that they can be considered pure elliptical galaxies. The remaining 3 galaxies are better fitted by a Sersic profile with index 1.9<n<2.3 suggesting that a disk-like component could contribute up to 30% to the total light of these galaxies. We derived the effective radius R_e and the mean surface brightness within R_e of our galaxies and we compared them with those of early-types at lower redshifts. We find that the surface brightness of our galaxies should get fainter by 2.5 mag from z~1.5 to z~0 to match the surface brightness of the local ellipticals with comparable R_e, i.e. the local Kormendy relation. Luminosity evolution without morphological changes can only explain half of this effect, as the maximum dimming expected for an elliptical galaxy is ~1.6 mag in this redshift range. Thus, other parameters, possibly structural, may undergo evolution and play an important role in reconciling models and observations. Hypothesizing an evolution of the effective radius of galaxies we find that R_e should increase by a factor 1.5 from z~1.5 to z~0.Comment: Accepted for publication in MNRAS, 15 pages, 8 figure