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We present a SINFONI integral field kinematical study of 33 galaxies at z~3 from the AMAZE and LSD projects which are aimed at studying metallicity and dynamics of high-redshift galaxies. The number of galaxies analyzed in this paper constitutes a significant improvement compared to existing data in the literature and this is the first time that a dynamical analysis is obtained for a relatively large sample of galaxies at z~3. 11 galaxies show ordered rotational motions (~30% of the sample), in these cases we estimate dynamical masses by modeling the gas kinematics with rotating disks and exponential mass distributions. We find dynamical masses in the range 2 \times 10^9 M\odot - 2 \times 10^11 M\odot with a mean value of ~ 2 \times 10^10 M\odot. By comparing observed gas velocity dispersion with that expected from models, we find that most rotating objects are dynamically "hot", with intrinsic velocity dispersions of the order of ~90 km s-1. The median value of the ratio between the maximum disk rotational velocity and the intrinsic velocity dispersion for the rotating objects is 1.6, much lower than observed in local galaxies value (~10) and slightly lower than the z~2 value (2 - 4). Finally we use the maximum rotational velocity from our modeling to build a baryonic Tully-Fisher relation at z~3. Our measurements indicate that z~3 galaxies have lower stellar masses (by a factor of ten on average) compared to local galaxies with the same dynamical mass. However, the large observed scatter suggests that the Tully-Fisher relation is not yet "in place" at these early cosmic ages, possibly due to the young age of galaxies. A smaller dispersion of the Tuly-Fisher relation is obtained by taking into account the velocity dispersion with the use of the S_0.5 indicator, suggesting that turbulent motions might have an important dynamical role., Comment: A&A accepted

We present a catalog of optical spectroscopic identifications of sources detected by Spitzer at 3.6 or 24 micron down to 10 and 280 microJy, respectively, in the SWIRE/XMM-Newton/ELAIS-S1 field and classified via line width analysis and diagnostic diagrams. A total of 1376 sources down to R~24.2 mag have been identified (1362 detected at 3.6 micron, 419 at 24 micron, and 405 at both) by low-resolution optical spectroscopy carried out with FORS2, VIMOS, and EFOSC2 at the Very Large Telescope and 3.6m ESO telescopes. The spectroscopic campaigns have been carried out over the central 0.6 square degrees area of ELAIS-S1 which, in particular, has also been observed by XMM-Newton and Chandra. We find the first direct optical spectroscopic evidence that the fraction of active galactic nuclei (AGN; mostly AGN2) increases with increasing F(24 micron)/F(R) ratio, reaching values of 70(+/-20)% in the range 316

We present initial results of an ESO-VLT large programme (AMAZE) aimed at determining the evolution of the mass-metallicity relation at z>3 by means of deep near-IR spectroscopy. Gas metallicities are measured, for an initial sample of nine star forming galaxies at z~3.5, by means of optical nebular lines redshifted into the near-IR. Stellar masses are accurately determined by using Spitzer-IRAC data, which sample the rest-frame near-IR stellar light in these distant galaxies. When compared with previous surveys, the mass-metallicity relation inferred at z~3.5 shows an evolution much stronger than observed at lower redshifts. The evolution is prominent even in massive galaxies, indicating that z~3 is an epoch of major action in terms of star formation and metal enrichment also for massive systems. There are also indications that the metallicity evolution of low mass galaxies is stronger relative to high mass systems, an effect which can be considered the chemical version of the galaxy downsizing. The mass-metallicity relation observed at z~3.5 is difficult to reconcile with the predictions of some hierarchical evolutionary models. Such discrepancies suggest that at z>3 galaxies are assembled mostly with relatively un-evolved sub-units, i.e. small galaxies with low star formation efficiency. The bulk of the star formation and metallicity evolution probably occurs once small galaxies are already assembled into bigger systems., Comment: 19 pages, 11 figures, A&A in press, replaced with accepted version

(ABRIDGED) We investigate here the XLF of absorbed (Nh between 4E21 and E24 cm-2) and unabsorbed (Nh < 4E21 cm-2) AGN, the fraction of absorbed AGN as a function of Lx (and z), the intrinsic Nh distribution of the AGN population, and the XLF of Compton Thick (Nh > E24 cm-2) AGN. To carry out this investigation we have used the XMM-Newton Hard Bright Serendipitous Sample (HBSS) a complete sample of bright X-ray sources (fx > 7E-14 cgs) at high galactic latitude (|b| > 20 deg) selected in the 4.5-7.5 keV energy band. The HBSS sample is now almost completely identified (97% spectroscopic ID) and it can be safely used for a statistical investigation. The HBSS contains 62 AGN out of which 40 are unabsorbed (or marginally absorbed; Nh < 4E21 cm-2) and 22 are absorbed (Nh between 4E21 and E24 cm-2). Absorbed and unabsorbed AGN are characterized by two different XLF with the absorbed AGN population being described by a steeper XLF, if compared with the unabsorbed ones, at all luminosities. The intrinsic fraction F of absorbed AGN with L(2-10 keV) > 3E42 cgs is 0.57+/-0.11; we find that F decreases with the intrinsic luminosity, and probably, increases with the redshift. Our data are consistent with a flat Log Nh distribution for Nh between E20 and E24 cm-2. Finally, by comparing the results obtained here with those obtained using an optically selected sample of AGN we derive, in an indirect way, the XLF of Compton Thick AGN. The density ratio between Compton Thick AGN (Nh > E24 cm-2) and Compton Thin AGN (Nh < E24 cm-2) decreases from 1.08+/-0.44 at Lx E43 cgs to 0.23+/-0.15 at Lx E45 cgs., Comment: Accepted for publication in A&A; 14 pages + 1 Appendix; 10 figures in the main text + 1 figure in the Appendix; 3 Tables

We present preliminary results of an ESO-VLT large programme (AMAZE) aimed at determining the evolution of the mass-metallicity relation at z~3 by means of deep near-IR spectroscopy. Gas metallicities and stellar masses are measured for an initial sample of nine star forming galaxies at z~3.3. When compared with previous surveys, the mass-metallicity relation inferred at z~3.3 shows an evolution significantly stronger than observed at lower redshifts. There are also some indications that the metallicity evolution of low mass galaxies is stronger relative to high mass systems, an effect which can be considered as the chemical version of the galaxy downsizing. The mass-metallicity relation observed at z~3.3 is difficult to reconcile with the predictions of some hierarchical evolutionary models. We shortly discuss the possible implications of such discrepancies., Comment: 6 pages, 4 figures, to appear in the proceedings of "A Century of Cosmology: Past, Present and Future" (Venezia, August 2007)

X-ray Bright Optically Normal Galaxies (XBONGs) constitute a small but not negligible fraction of hard X-ray selected sources in recent Chandra and XMM-Newton surveys. Even though several possibilities were proposed to explain why a relatively luminous hard X-ray source does not leave any significant signature of its presence in terms of optical emission lines, the nature of XBONGs is still subject of debate. We aim to a better understanding of their nature by means of a multiwavelength and morphological analysis of a small sample of these sources. Good-quality photometric near-infrared data (ISAAC/VLT) of four low-redshift (z=0.1-0.3) XBONGs, selected from the HELLAS2XMM survey, have been used to search for the presence of the putative nucleus, applying the surface-brightness decomposition technique through the least-squares fitting program GALFIT. The surface brightness decomposition allows us to reveal a nuclear point-like source, likely to be responsible of the X-ray emission, in two out of the four sources. The results indicate that moderate amounts of gas and dust, covering a large solid angle (possibly 4pi) at the nuclear source, combined with the low nuclear activity, may explain the lack of optical emission lines. The third XBONG is associated with an X-ray extended source and no nuclear excess is detected in the near infrared at the limits of our observations. The last source is associated to a close (d< 1 arcsec) double system and the fitting procedure cannot achieve a firm conclusion., Comment: 20 pages, 12 figures, A&A in press

AIMS: We present the optical classification and redshift of 348 X-ray selected sources from the XMM-Newton Bright Serendipitous Survey (XBS) which contains a total of 400 objects (identification level = 87%). About 240 are new identifications. In particular, we discuss in detail the classification criteria adopted for the Active Galactic Nuclei population. METHODS: By means of systematic spectroscopic campaigns and through the literature search we have collected an optical spectrum for the large majority of the sources in the XBS survey and applied a well-defined classification ``flow-chart''. RESULTS: We find that the AGN represent the most numerous population at the flux limit of the XBS survey (~10^-13 erg cm^-2 s^-1) constituting 80% of the XBS sources selected in the 0.5-4.5 keV energy band and 95% of the ``hard'' (4.5-7.5 keV) selected objects. Galactic sources populate significantly the 0.5-4.5 keV sample (17%) and only marginally (3%) the 4.5-7.5 keV sample. The remaining sources in both samples are clusters/groups of galaxies and normal galaxies (i.e. probably not powered by an AGN). Furthermore, the percentage of type2 AGN (i.e. optically absorbed AGNs with A_V>2mag) dramatically increases going from the 0.5-4.5 keV sample (f=N_AGN2/N_AGN=7%) to the 4.5-7.5 keV sample (f=32%). We finally propose two simple diagnostic plots that can be easily used to obtain the spectral classification for relatively low redshift AGNs even if the quality of the spectrum is not good., Comment: 14 pages plus 7 additional pages of table, accepted for publication on A&A

(Abridged) We present the results of the photometric and spectroscopic identification of 110 hard X-ray selected sources (6e-15 1000, while their Lx, L(R) and Nh are similar. This suggests that while the central engine of narrow-line AGNs and XBONGs looks similar, the narrow-line region in XBONGs could be strongly inhibited or obscured., Comment: Accepted for publication in A&A, 18 pages, 19 figures

We discuss here the main goals and some interesting results of the "XMM-Newton Bright Serendipitous Survey", a research program conducted by the XMM-Newton Survey Science Center in two complementary energy bands (0.5-4.5 keV and 4.5-7.5 keV) in the bright (>~7E-14) flux regime. The very high identification rate (96%) for the X-ray source sample selected in the 4.5-7.5 keV band is used here to have, in this energy range, an "unbiased" view of the extragalactic hard X-ray sky at bright fluxes., Comment: 6 pages, 3 figures, proceedings of the conference "The X-ray Universe 2005", held in San Lorenzo de El Escorial, Spain, 26-30 September 2005, organized by the European Space Astronomy Centre (ESAC) of ESA

We present VLT near-IR spectroscopic observations of three X-ray sources characterized by extremely high X-ray-to-optical ratios (X/O>40), extremely red colors (6.3

We have determined the cosmological evolution of the density of AGN and of their Nh distribution as a function of the un-absorbed 2-10 keV luminosity up to redshift 4. We used the HELLAS2XMM sample combined with other published catalogs, yielding a total of 508 AGN. Our best fit is obtained with a luminosity-dependent density evolution (LDDE) model where low luminosity (Lx~10^43 erg s^-1) AGN peak at z~0.7, while high luminosity AGN (Lx>10^45 erg s^-1) peak at z~2.0. A pure luminosity evolution model (PLE) can instead be rejected. There is evidence that the fraction of absorbed (Nh>10^22 cm^-2) AGN decreases with the intrinsic X-ray luminosity, and increases with the redshift. Our best fit solution provides a good fit to the observed counts, the cosmic X-ray background, and to the observed fraction of absorbed AGN as a function of the flux in the 10^-1510^44 erg s^-1) AGN have a density of 267 deg^-2 at fluxes S(2-10)>10^-15 erg s^-1 cm^-2. Using these results, we estimate a density of supermassive black holes in the local Universe of 3.2 (h^2_70) x 10^5 M_sol Mpc^-3, which is consistent with the recent measurements of the black hole mass function in the local galaxies., Comment: 16 pages, 20 figures. Scheduled on ApJ, Vol. 635, 2005 December 20

We present a statistical analysis of the Chandra observation of the source field around the 3C 295 galaxy cluster (z=0.46) aimed at the search for clustering of X-ray sources. Three different methods of analysis, namely a chip by chip logN-logS, a two dimensional Kolmogorov-Smirnov test, and the angular correlation function (ACF) show a strong overdensity of sources in the North-East of the field. In particular, the ACF shows a clear signal on scales of 0.5 - 5 arcmin. This correlation angle is > 2 times higher than that of a sample of 8 ACIS-I field at the 2.5 sigma confidence level. If this overdensity is spatially associated to the cluster, we are observing a 'filament' of the large scale structure of the Universe. We discuss some first results that seem to indicate such an association., Comment: 4 pages, 8 ps figures, proceeding of the 6th italian workshop on AGNs

We present a statistical analysis of the Chandra observation of the source field around the 3C 295 galaxy cluster (z=0.46). Three different methods of analysis, namely a chip by chip logN-logS, a two dimentional Kolmogorov-Smirnov (KS) test, and the angular correlation function (ACF) show a strong overdensity of sources in the North-East of the field, that may indicate a filament of the large scale structure of the Universe toward 3C 295., Comment: Proceeding of the workshop "Outskirts of Galaxy Clusters: intense life in the suburbs" Turin, March 12-16, 2004; 3 pages, 6 .ps figures

The spectroscopic analysis of 117 serendipitous sources in the HELLAS2XMM 1df (1 degree field) survey is described. Of these, 106 sources, of which 86% have a spectroscopic redshift, are used to evaluate the fraction of X-ray absorbed (log NH>22) Active Galactic Nuclei (AGN) in the 2--10 keV flux range 0.8-20E-14 erg/cm2/s. This fraction turns out lower than what is predicted by two well known Cosmic X-Ray Background synthesis models, and the discrepancy is significant at the 99.999% level. This result consolidates the findings recently obtained by other authors. In the flux interval explored, the data are consistent with an intrinsic distribution of the absorbing columns (flat per decade above logNH>21) independent of luminosity and redshift, together with an AGN luminosity function evolving purely in luminosity. It is shown that, on the other hand, extrapolation to lower fluxes fails to reproduce the results inferred from the Chandra Deep Field North survey. It is found that about 40% of the high luminosity sources in our sample have best fit logNH>22, and the surface density of these X-ray obscured QSOs can then be estimated at about 48 per square degree, at the flux limit of ~1E-14} erg/cm2/s of the HELLAS2XMM 1df survey. As a side issue, 5 or 6 out of 60 sources, that is about 10%, identified with broad line AGN, turn out to be affected by logNH>22 absorption., Comment: A&A in press

We present a multi-wavelength catalog (15 um, R, K-band, 1.4 GHz flux) plus spectroscopic identifications for 406 15 um sources detected in the ELAIS region S1, over the flux density range 0.5

We present the results of deep near-infrared observations of 11 hard X-ray selected sources in the Hellas2XMM survey, with faint optical magnitude (R>24) and high X-ray-to-optical flux ratio. All but one of the sources have been detected in the Ks band, with bright counterparts (Ks<19) and red colors (R-K>5), and therefore belong to the ERO population. A detailed analysis of the surface brightness profiles allows us to classify all of the NIR counterparts. There are 2 point-like objects, 7 elliptical galaxies and one source with a disky profile. None of the extended sources shows any evidence for the presence of a central unresolved object tracing the putative X-ray emitting AGN. Using both the R-K colors and the morphological information, we have estimated for all the sources a ``minimum photometric redshift'', ranging between 0.8 and 2.4; the elliptical hosts have zmin=0.9-1.4. We computed the X-ray properties using these redshifts: most of the sources have NH>10^{22}, with unabsorbed X-ray luminosities up to 10^{45}erg s^{-1}. These objects therefore belong to the population of obscured (Type II) quasars and, from a statistical point of view, they turn out to be a non-negligible fraction (~10%) of the most luminous AGN. Selecting the high X/O sources for a follow-up study in the NIR is therefore a powerful technique aimed at studying at high redshift the hosts of Type II AGN. Overall, our results seem to indicate that the hosts are mostly elliptical galaxies at z~1, and that these near-IR bright objects would be among the most massive spheroids at these epochs., Comment: 15 pages, 8 figures. Accepted for publication in A&A. V2: minor typos corrected

We present results from the photometric and spectroscopic identification of 122 X-ray sources discovered by XMM-Newton in the 2-10 keV band (the HELLAS2XMM 1dF sample). One of the most interesting results (which is found also in deeper sourveys) is that ~20% of the sources have an X-ray to optical flux ratio (X/O) ten times or more higher than that of optically selected AGN. Unlike the faint sources found in the ultra-deep Chandra and XMM-Newton surveys, which reach X-ray (and optical) fluxes >~10 times lower than in the HELLAS2XMM sample, many of the extreme X/O sources in our sample have R~25 and are therefore accessible to optical spectroscopy. We report the identification of 13 sources with extreme X/O values. While four of these sources are broad line QSO, eight of them are narrow line QSO, seemingly the extension to very high luminosity of the type 2 Seyfert galaxies., Comment: To appear in Proceeding of the "Multi-Wavelength Cosmology" Conference held in Mykonos, Greece, June 2003, ed.M. Plionis (Kluwer)

We present extensive optical, radio and infrared follow-up observations of a sample of 35 hard X-ray (2-10 keV) selected sources discovered serendipitously in the PV XMM-Newton observation of the radio-loud quasar PKS 0312-77 field, for which also an archival Chandra observation is available. The observations have been carried out as part of the HELLAS2XMM survey, a program aimed to understand the nature of the sources responsible for the bulk of the hard X-ray Background (XRB). The identification of the optical counterparts greatly benefits from the positional accuracy obtained from Chandra and radio observations. As a consequence, the spectroscopic completeness of the present sample (80%) is limited only by the faintness of the optical counterparts. The multiwavelength coverage of our survey allows us to unveil a large spread in the overall properties of hard X-ray selected sources. At low redshift (z<1), the source breakdown includes Broad Line AGN, Narrow Emission-Line Galaxies, and optically ``normal'' galaxies. All the ten sources at z>1 are spectroscopically classified as Broad Line AGNs. A few of them show significant intrinsic X-ray absorption (N(H)>10^22 cm^-2), further supporting previous evidence of a decoupling between optical and X-ray properties at high luminosities and redshifts. Finally, a non negligible fraction (15%) of the hard X-ray sources are not detected down to the limiting magnitude of the optical images. The corresponding high X-ray to optical flux ratio, X-ray and optical-infrared colors strongly suggest that they are high redshift, obscured AGN., Comment: 16 pages, 10 figures, accepted for publication in Astronomy & Astrophysics (aa.cls included)

We present results from the photometric and spectroscopic identification of 122 X-ray sources recently discovered by XMM-Newton in the 2-10 keV band (the HELLAS2XMM 1dF sample). Their flux cover the range 8E-15-4E-13 cgs and the total area surveyed is 0.9 deg2. About 20% of the hard X-ray selected sources have an X-ray to optical flux ratio (X/O) ten times or more higher than that of optically selected AGN. Unlike the faint sources found in the ultra-deep Chandra and XMM-Newton surveys, which reach X-ray (and optical) fluxes more than one order of magnitude lower than the HELLAS2XMM survey sources, many of the extreme X/O sources in our sample have R<=25 and are therefore accessible to optical spectroscopy. We report the identification of 13 sources with X/O>10: 8 are narrow line QSO (i.e. QSO2), four are broad line QSO. We use a combined sample of 317 hard X-ray selected sources (HELLAS2XMM 1dF, CDFN 1Msec, SSA13 and Lockman Hole flux limited samples), 221 with measured z, to evaluate the cosmological evolution of the hard X-ray source's number and luminosity densities. Looking backward in time, the low luminosity sources (logL(2-10keV) = 43-44 erg/s) increase in number at a rate different than the high luminosity sources (logL(2-10keV)>44.5 erg/s), reaching a maximum around z=1 and then levelling off beyond z=2. This translates into an accretion driven luminosity density which is dominated by sources with logL(2-10keV) < 44.5 erg/s up to at least z=1, while the contribution of the same sources and of those with logL(2-10keV)>44.5 erg/s appear to be comparable between z=2 and 4., Comment: v2, minor changes, A&A in press