Search

We present the X-ray luminosity function of AGN in three energy bands (Soft: 0.5-2 keV, Hard: 2-10 keV and Ultrahard: 4.5-7.5 keV). We have used the XMS survey along with other highly complete flux-limited deeper and shallower surveys for a total of 1009, 435 and 119 sources in the Soft, Hard and Ultrahard bands, respectively. We have modeled the intrinsic absorption of the Hard and Ultrahard sources (NH function) and computed the intrinsic X-ray luminosity function in all bands using a Maximum Likelihood fit technique to an analytical model. We find that the X-ray luminosity function (XLF) is best described by a Luminosity-Dependent Density Evolution (LDDE) model. Our results show a good overall agreement with previous results in the Hard band, although with slightly weaker evolution. Our model in the Soft band present slight discrepancies with other works in this band, the shape of our present day XLF being significantly flatter. We find faster evolution in the AGN detected in the Ultrahard band than those in the Hard band. The fraction of absorbed AGN in the Hard and Ultrahard bands is dependent on the X-ray luminosity. We find evidence of evolution of this fraction with redshift in the Hard band but not in the Ultrahard band, possibly due to the low statistics. Our best-fit XLF shows that the high-luminosity AGN are fully formed earlier than the less luminous AGN. The latter sources account for the vast majority of the accretion rate and mass density of the Universe, according to an anti-hierarchical black hole growth scenario., Comment: 16 pages, 12 figures, accepted for publication in Astronomy and Astrophysics

We have constrained the extragalactic source count distributions over a broad range of X-ray fluxes and in various energy bands to test whether the predictions from X-ray background synthesis models agree with the observational constraints provided by our measurements. We have used 1129 XMM-Newton observations at |b|>20 deg covering a sky area of 132.3 deg^2 to compile the largest complete samples of X-ray objects to date in the 0.5-1 keV, 1-2 keV, 2-4.5 keV, 4.5-10 keV, 0.5-2 keV and 2-10 keV energy bands. Our survey includes in excess of 30,000 sources down to ~10^-15 erg/cm^2/s below 2 keV and down to ~10^{-14} erg/cm^2/s above 2 keV. A break in the source count distributions was detected in all energy bands except the 4.5-10 keV band. An analytical model comprising 2 power-law components cannot adequately describe the curvature seen in the source count distributions. The shape of the logN(>S)-logS is strongly dependent on the energy band with a general steepening apparent as we move to higher energies. This is due to non-AGN populations, comprised mainly of stars and clusters of galaxies, contribute up to 30% of the source population at energies <2 keV and at fluxes >10^{-13} erg/cm^2/s, and these populations of objects have significantly flatter source count distributions than AGN. We find a substantial increase in the relative fraction of hard X-ray sources at higher energies, from >55% below 2 keV to >77% above 2 keV. However the majority of sources detected above 4.5 keV still have significant flux below 2 keV. Comparison with predictions from the synthesis models suggest that the models might be overpredicting the number of faint absorbed AGN, which would call for fine adjustment of some model parameters such as the obscured to unobscured AGN ratio and/or the distribution of column densities at intermediate obscuration., Comment: Accepted for publication in Astronomy and Astrophysics. Abridged Abstract. 23 pages, 47 figures, 8 tables

Aims: Pointed observations with XMM-Newton provide the basis for creating catalogues of X-ray sources detected serendipitously in each field. This paper describes the creation and characteristics of the 2XMM catalogue. Methods: The 2XMM catalogue has been compiled from a new processing of the XMM-Newton EPIC camera data. The main features of the processing pipeline are described in detail. Results: The catalogue, the largest ever made at X-ray wavelengths, contains 246,897 detections drawn from 3491 public XMM-Newton observations over a 7-year interval, which relate to 191,870 unique sources. The catalogue fields cover a sky area of more than 500 sq.deg. The non-overlapping sky area is ~360 sq.deg. (~1% of the sky) as many regions of the sky are observed more than once by XMM-Newton. The catalogue probes a large sky area at the flux limit where the bulk of the objects that contribute to the X-ray background lie and provides a major resource for generating large, well-defined X-ray selected source samples, studying the X-ray source population and identifying rare object types. The main characteristics of the catalogue are presented, including its photometric and astrometric properties ., Comment: 27 pages (plus 8 pages appendices), 15 figures. Minor changes following referee's comments; now accepted for publication in A & A. Note that this paper "V", not paper "VI" in the series. Previous posting was incorrect in this regard

(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

Simbol-X is a French-Italian mission, with a participation of German laboratories, for X-ray astronomy in the wide 0.5-80 keV band. Taking advantage of emerging technology in mirror manufacturing and spacecraft formation flying, Simbol-X will push grazing incidence imaging up to ~80 keV, providing an improvement of roughly three orders of magnitude in sensitivity and angular resolution compared to all instruments that have operated so far above 10 keV. This will open a new window in X-ray astronomy, allowing breakthrough studies on black hole physics and census and particle acceleration mechanisms. We describe briefly the main scientific goals of the Simbol-X mission, giving a few examples aimed at highlighting key issues of the Simbol-X design., Comment: Proc. of the workshop "Simbol-X: The hard X-ray universe in focus", Bologna 14-16 May, 2007

We will briefly discuss the importance of sensitive X-ray observations above 10 keV for a better understanding of the physical mechanisms associated to the Supermassive Black Hole primary emission and to the cosmological evolution of the most obscured Active Galactic Nuclei., Comment: 6 pages, 5 figures, to appear in proceedings of "Simbol-X: the hard X-ray Universe in focus", held in Bologna (Italy), May 14-16, 2007

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

We present the XMM-Newton Medium sensitivity Survey (XMS), including a total of 318 X-ray sources found among the serendipitous content of 25 XMM-Newton target fields. The XMS comprises four largely overlapping source samples selected at soft (0.5-2 keV), intermediate (0.5-4.5 keV), hard (2-10 keV) and ultra-hard (4.5-7.5 keV) bands, the first three of them being flux-limited. We report on the optical identification of the XMS samples, complete to 85-95%. At the intermediate flux levels sampled by the XMS we find that the X-ray sky is largely dominated by Active Galactic Nuclei. The fraction of stars in soft X-ray selected samples is below 10%, and only a few per cent for hard selected samples. We find that the fraction of optically obscured objects in the AGN population stays constant at around 15-20% for soft and intermediate band selected X-ray sources, over 2 decades of flux. The fraction of obscured objects amongst the AGN population is larger (~35-45%) in the hard or ultra-hard selected samples, and constant across a similarly wide flux range. The distribution in X-ray-to-optical flux ratio is a strong function of the selection band, with a larger fraction of sources with high values in hard selected samples. Sources with X-ray-to-optical flux ratios in excess of 10 are dominated by obscured AGN, but with a significant contribution from unobscured AGN., Comment: A&A, accepted

According to the latest versions of synthesis modeling of the Cosmic X-ray Background, Compton Thick AGN should represent ~50% of the total absorbed AGN population. However, despite their importance in the cosmological context, only a few dozens of Compton Thick AGN have been found and studied so far. We will briefly review this topic and discuss the improvement in this field offered by the Simbol-X mission with its leap in sensitivity (E>10 keV) of more than a factor 500 with respect to previous X-ray missions., Comment: Solicited talk at the conference "Simbol-X: the Hard X-ray Universe in focus" held in Bologna, 14-16 May 2007. 8 pages, 5 figures, 2 tables

We present the results of infrared L-band (3-4 micron) and M-band (4-5 micron) VLT-ISAAC spectroscopy of five bright Ultraluminous InfraRed Galaxies (ULIRGs) hosting an AGN. From our analysis we distinguish two types of sources: ULIRGs where the AGN is unobscured (with a flat continuum and no absorption features at 3.4 micron and 4.6 micron), and those with highly obscured AGNs (with a steep, reddened continuum and absorption features due to hydrocarbons and CO). Starburst activity is also present in all of the sources as inferred from the 3.3 micron PAH emission line. A strong correlation is found between continuum slope and CO optical depth, which suggests that deep carbon monoxide absorption is a common feature of highly obscured ULIRG AGN. Finally we show that the AGN dominates the 3-4 micron emission, even if its contribution to the bolometric luminosity is small., Comment: 24 pages, 4 figures, accepted for publication in ApJ

AIMS: We investigate here the nature of all the sources (35 in total) in the XBS survey (which is 86% optically identified) showing an optical spectrum dominated by the light from the host galaxy with no evidence (or little evidence) for the presence of an AGN. METHODS: We use the X-ray spectral analysis to assess the presence of an AGN in these sources and to characterize its properties. RESULTS: We detect AGN activity in 33 out of 35 sources. The remaining 2 sources are the ones with the lowest X-ray luminosity in the sample (L[2-10keV]<10^41 erg s^-1) and their X-ray emission could be produced within the host galaxy. We find that the ``recognition problem'' for AGN is very critical in the low-luminosity regime (at least 60% of the AGN with L[2-10keV]<10^43 erg s^-1 are elusive) becoming negligible for high X-ray luminosities (~1.5% of elusive AGN with L[2-10keV]>10^44 erg s^-1). This problem affects mostly absorbed AGN (~40% of type~2 AGN in the survey are elusive) but also a significant fraction of unabsorbed AGN (8%). CONCLUSIONS: We find that the simplest explanations of why these 33 (or most of them) AGNs are elusive are two: at low X-ray luminosities (<10^43 erg s^-1) the most important reason is the intrinsically low AGN/galaxy contrast (optical dilution) while at high luminosities (>10^44 erg s^-1) it is due to the optical absorption (in the Compton-thin regime, i.e. NH<10^24 cm^-2). Alternative hypotheses, like the presence of Compton-thick sources, BL Lac objects or ``non-standard'' AGN (e.g. with alpha_OX<1 or with weak/absorbed Narrow Line Region) are not supported by the data although we cannot exclude the presence in the sample of a few sources of these types., Comment: accepted for publication in A&A, 17 pages, 9 figures

We present optical and X-ray data for a sample of serendipitous XMM-Newton sources that are selected to have 0.5-2 keV vs 2-4.5 keV X-ray hardness ratios which are harder than the X-ray background. The sources have 2-4.5 keV X-ray flux >= 10^-14 cgs, and in this paper we examine a subsample of 42 optically bright (r < 21) sources; this subsample is 100 per cent spectroscopically identified. All but one of the optical counterparts are extragalactic, and we argue that the single exception, a Galactic M star, is probably a coincidental association. The X-ray spectra are consistent with heavily absorbed power laws (21.8 < log NH < 23.4), and all of them appear to be absorbed AGN. The majority of the sources show only narrow emission lines in their optical spectra, implying that they are type-2 AGN. Only a small fraction of the sources (7/42) show broad optical emission lines, and all of these have NH < 10^23 cm^-2. This implies that ratios of X-ray absorption to optical/UV extinction equivalent to > 100 times the Galactic gas-to-dust ratio are rare in AGN absorbers (at most a few percent of the population), and may be restricted to broad absorption-line QSOs. Seven objects appear to have an additional soft X-ray component in addition to the heavily absorbed power law. We consider the implications of our results in the light of the AGN unified scheme. We find that the soft components in narrow-line objects are consistent with the unified scheme provided that > 4 per cent of broad-line AGN have ionised absorbers that attenuate their soft X-ray flux by >50 per cent. In at least one of the X-ray absorbed, broad-line AGN in our sample the X-ray spectrum requires an ionised absorber, consistent with this picture., Comment: accepted for publication in MNRAS

AXIS (An XMM-Newton International Survey) is a survey of 36 high Galactic latitude XMM-Newton observations covering 4.8 deg2 and containing 1433 serendipitous X-ray sources detected with 5-sigma significance. We have studied the X-ray source counts in four energy bands soft (0.5-2 keV), hard (2-10 keV), XID (0.5-4.5 keV) and ultra-hard (4.5-7.5 keV). We have combined this survey with shallower and deeper surveys. Our source counts results are compatible with most previous samples in the soft, XID, ultra-hard and hard bands. The fractions of the XRB resolved in the surveys used in this work are 87%, 85%, 60% and 25% in the soft, hard, XID and ultra-hard bands, respectively. Extrapolation of our source counts to zero flux are not enough to saturate the XRB intensity. Only galaxies and/or absorbed AGN may be able contribute the remaining unresolved XRB intensity. Our results are compatible, within the errors, with recent revisions of the XRB intensity in the soft and hard bands. The maximum fractional contribution to the XRB comes from fluxes within about a decade of the break in the source counts (~1e-14 cgs), reaching ~50% of the total in the soft and hard bands. Using only AXIS sources, we have studied the angular correlation in those bands using a novel robust technique. Angular clustering (widely distributed over the sky and not confined to a few deep fields) is detected at 99-99.9% significance in the soft and XID bands, with no detection in the hard and ultra-hard band (probably due to the smaller number of sources). We cannot confirm the detection of significantly stronger clustering in the hard-spectrum hard sources. Medium depth surveys such as AXIS are essential to determine the evolution of the X-ray emission in the Universe below 10 keV., Comment: 28 pages, 10 figures, A&A accepted

Context: The comparison of observed counts in a given sky direction with predictions by Galactic models yields constraints to the spatial distribution and the stellar birthrate of young stellar populations. In this work we present the results of the analysis of the stellar content of the XMM-Newton Bright Serendipitous Survey (XBSS). This unbiased survey includes a total of 58 stellar sources selected in the 0.5 -- 4.5 keV energy band, having a limiting sensitivity of $10^{-2}$ cnt s$^{-1}$ and covering an area of 28.10 sq. deg. Aims: Our main goal is to understand the recent star formation history of the Galaxy in the vicinity of the Sun. Methods: We compare the observations with the predictions obtained with XCOUNT, a model of the stellar X-ray content of the Galaxy. The model predicts the number and properties of the stars to be observed in terms of magnitude, colour, population and $f_\mathrm{x}/f_\mathrm{v}$ ratio distributions of the coronal sources detected with a given instrument and sensitivity in a specific sky direction. Results: As in other shallow surveys, we observe an excess of stars not predicted by our Galaxy model. Comparing the colours of the identified infrared counterparts with the model predictions, we observe that this excess is produced by yellow (G+K) stars. The study of the X-ray spectrum of each source reveals a main population of stars with coronal temperature stratification typical of intermediate-age stars. As no assumptions have been made for the selection of the sample, our results must be representative of the entire Solar Neighbourhood. Some stars show excess circumstellar absorption indicative of youth., Comment: Accepted for publication in Astronomy and Astrophysics: 02/10/2006

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 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 figures

The optical rest-frame sizes of 10 of the most massive (~5x10^{11}h_{70}^{-2}M_sun) galaxies found in the near-infrared MUNICS survey at 1.2

We present the XMM-Newton and the optical-VLT spectra along with the optical and the near-infrared photometric data of one of the brightest X-ray (F(2-10 keV)~1e-13 erg/s cm^2) extremely red objects (R-K>=5) discovered so far. The source, XBSJ0216-0435, belongs to the XMM-Newton Bright Serendipitous Survey and it has extreme X-ray-to-optical (~220) and X-ray-to-near-infrared (~60) flux ratios. Thanks to its brightness, the X-ray statistics are good enough for an accurate spectral analysis by which the presence of an X-ray obscured (NH>1e22 cm^-2) QSO (L(2-10 keV)=4e45 erg/s) is determined. A statistically significant (~99%) excess around 2 keV in the observed-frame suggests the presence of an emission line. By assuming that this feature corresponds to the iron Kalpha line at 6.4 keV, a first estimate of the redshift of the source is derived (z_x~2). The presence of a high redshift QSO2 has been finally confirmed through dedicated VLT optical spectroscopic observations (z_o=1.985+/-0.002). This result yields to an optical validation of a new X-ray Line Emitting Object (XLEO) for which the redshift has been firstly derived from the X-ray data. XBSJ0216-0435 can be considered one of the few examples of X-ray obscured QSO2 at high redshift for which a detailed X-ray and optical spectral analysis has been possible. The spectral energy distribution from radio to X-rays is also presented. Finally from the near-infrared data the luminosity and the stellar mass of the host galaxy has been estimated finding a new example of the coexistence at high-z between massive galaxies and powerful QSOs., Comment: Accepted for publication on A&A; 7 pages, 6 figures

We present 3-5 micron spectroscopy of the interacting system NGC 6240, showing the presence of two active galactic nuclei. The brightest (southern) nucleus shows up with a starburst-like emission, with a prominent 3.3 micron emission feature. However, the presence of an AGN is revealed by the detection of a broad Br alpha emission line, with a width of ~1,800 km/s. The spectrum of the faintest (northern) nucleus shows typical AGN features, such as a steep continuum and broad absorption features in the M-band. We discuss the physical properties of the dusty absorbers/emitters, and show that in both nuclei the AGN is dominant in the 3-5 micron band, but its contribution to the total luminosity is small (a few percent of the starburst emission)., Comment: 10 pages, 2 figures, accepted for publication in ApJ Letters

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 the results of L-band spectroscopical observations of local bright ULIRGs, performed with ISAAC at the VLT. We discuss the L-band spectral features of seven single sources, and the statistical properties of a complete sample of 15 sources obtained combining our observations with other published 3-4 micron spectra. Our main results are: 1. When a spectral indicator suggesting the presence of an AGN (low equivalent width of the 3.3 micron emission line, steep lambda-f_lambda spectrum, presence of an absorption feature at 3.4 micron) is found, the AGN is always confirmed by independent analysis at other wavelengths. Conversely, in all known AGNs at least one of the above indicators is present. 2. Two new diagnostic diagrams are proposed combining the above indicators, in which starbursts and AGNs are clearly and completely separated. 3. The above diagnostic techniques are possible with spectra of relatively low quality, which can be obtained for several tens of ULIRGs with currently available telescopes. This makes L-band spectroscopy the current best tool to disentangle AGNs and starbursts contributions in ULIRGs. 4. The L-band properties of ULIRGs are heterogeneous. However, we show that all the spectral differences among ULIRGs can be reproduced starting from pure intrinsic AGN and SB spectra and varying two parameters: the amount of dust extinction of the AGN component, and the relative AGN/SB contribution to the bolometric luminosity. 5. Using the above decomposition model, we show that AGNs in ULIRGs have a low dust-to-gas ratio and a dust extinction curve different from Galactic. 6. The estimate of the contribution of AGNs in a complete sample show that AGNs are hosted by ~2/3 of ULIRGs, but their energetic contribution is relevant only in ~20% of the sample., Comment: 20 Pages, 7 figures, accepted for publication in MNRAS

Results obtained from an X-ray spectral survey of nearby Seyfert galaxies using XMM--Newton are reported. The sample was optically selected, well defined, complete in B mag, and distance limited: it consists of the nearest (D<22 Mpc) 27 Seyfert galaxies (9 of type 1, 18 of type 2) taken from the Ho et al. (1997) sample. This is one of the largest atlases of hard X-ray spectra of low-L active galaxies ever assembled. All nuclear sources except two Sey 2s are detected between 2-10 keV, half for the first time ever, and average spectra are obtained for all of them. Nuclear luminosities reach values down to 10**38 erg/s. The shape of the distribution of X-ray parameters is affected by the presence of Compton-thick objects (> 30% among type 2s). The latter have been identified either directly from their intense FeK line and flat X-ray spectra, or indirectly with flux diagnostic diagrams which use isotropic indicators. After taking into account these highly absorbed sources, we find that (i) the intrinsic X-ray spectral properties (i.e., spectral shapes and luminosities above 2 keV) are consistent between type 1 and type 2 Sey, as expected from ``unified models'', (ii) Sey galaxies as a whole are distributed fairly continuously over the entire range of Nh, between 10**20 and 10**25 cm**-2, and (iii) while Sey 1s tend to have lower Nh and Sey 2s tend to have the highest, we find 30% and 10% exceptions, respectively. Overall the sample well represents the average intrinsic X-ray spectral properties of nearby AGN, including a proper estimate of the distribution of their absorbing columns. Finally, we conclude that, with the exception of a few cases, the present study agrees with predictions of unified models of Sey galaxies, and extends their validity down to very low luminosities., Comment: 23 pages, 4 tables, 4 figures, 2 Appendices with 27 source spectra and notes, to be published in the Astronomy & Astrophysics Journal

This paper presents new Chandra and BeppoSAX observations aimed at investigating the optical/X-ray mismatch in the enigmatic class of the Composite galaxies, discovered by a cross-correlation of IRAS and ROSAT all sky survey catalogues. These galaxies have been classified as star-forming objects on the basis of their optical spectra, while the detection of weak broad wings in the H(alpha) emission in a few of them and their high X-ray luminosity in the ROSAT band indicated the presence of an active nucleus. The analysis of Chandra observations for 4 Composites has revealed nuclear point-like sources, with a typical AGN spectrum (Gamma = 1.7-1.9) and little intrinsic absorption. A strong flux variability has been observed on different time scales, in particular most of the sources were brighter at the ROSAT epoch. Although of relative low luminosity for the AGN class (L(2-10 keV) = 3-60 x 10^{41} erg/s), the active nucleus is nevertheless dominant in the X-ray domain. At other wavelengths it appears to be overwhelmed by the starburst and/or host galaxy light, yielding the Composite classification for these objects., Comment: 20 pages, 10 figures, accepted by ApJ

We present the analysis of 10 massive early-type galaxies at $z\sim1.5$. They have been identified by means of a near-IR low resolution spectroscopic follow-up of a complete sample of 36 bright (K' $<$ 18.5) Extremely Red Objects (EROs, R-K'$>$ 5) selected from the Munich Near-IR ClusterSurvey (MUNICS; Drory et al. 2001). The low resolution near-IR spectra constrain their redshift at $1.2 2$ for all the galaxies and $z_{f} \geq 4$ for the oldest ones. The comparison of the 4000\AA break and of the overall spectral shape of the average spectrum of the 10 galaxies at $z\sim1.5$ with those of their local counterpartsconfirms that field massive early-type galaxies formed the bulk of their stellar mass at $2

The XMM-Newton observation of the optically Type 1 AGN AXJ0447-0627 (z=0.214) unambiguously reveals a complex, bright and prominent set of lines in the 4-8 keV rest frame energy range. Although, from a phenomenological point of view, the observed properties can be described by a simple power law model plus 5 narrow Gaussian lines (at rest frame energies of nearly 4.49, 5.55, 6.39, 7.02 and 7.85 keV), we find that a model comprising a power law (Gamma of the order of 2.2), a reflected relativistic continuum, a narrow Fe I Kalpha line from neutral material as well as a broad Fe Kalpha relativistic line from a ionized accretion disk represents a good physical description of the data. The ''double horned'' profile of the relativistic line implies an inclination of the accretion disk of the order of 45 degree, and an origin in a narrow region of the disk, from R_in of the order of 19 GM/c^2 to R_out of the order of 30 GM/c^2. The narrow Fe I Kalpha line from neutral material is probably produced far from the central black hole, most likely in the putative molecular torus. Although some of these properties have been already found in other Type 1 AGN and discussed in the literature, at odd with the objects reported so far we measure high equivalent widths (EWs) of the observed lines: nearly 1.4 keV for the ``double horned'' relativistic line and nearly 0.4 keV for the narrow line., Comment: 16 pages, 3 figures, Latex manuscript; accepted for publication in ApJ

We present the first optical validation of an X-ray Line-Emitting Object (XLEO) discovered in the XMM-Newton observation of the Chandra Deep Field South. The object is an AGN at z_x ~ 0.66. An optical spectrum of the source indeed confirms and refines (z_o = 0.665) the redshift obtained from the X-ray line. The X-ray and optical properties of the source are presented and discussed., Comment: 13 pages, 3 figures. Accepted for publication by ApJL

We spectroscopically identified 7 massive evolved galaxies with magnitudes 17.8~1.5, a factor 1.5 lower than the density (8.4(+-1) x 10^{-5} Mpc^{-3}) of early-types with comparable masses at z=0. The incompleteness (30%) of our spectroscopic observations accounts for this discrepancy. Thus, our data do not support a decrease of the comoving density of early-type galaxies with masses comparable to the most massive ones in the local Universe up to z~1.7. This suggests that massive evolved galaxies do not play an important role in the evolution of the mass density outlined by recent surveys in this redshift range, evolution which instead has to be ascribed to the accretion of the stellar mass in late-type galaxies. Finally, the presence of such massive evolved galaxies at these redshifts suggests that the assembly of massive spheroids has taken place at z>2 supporting a high efficiency in the accretion of the stellar mass in massive halos in the early Universe., Comment: Accepted for publication in MNRAS Letters, 5 pages, 3 figures

We present preliminary results from a novel search for X-ray Line Emitting Objects (XLEOs) in XMM-Newton images. Three sources have been detected in a test-run analysis of 13 XMM-Newton observations. The three objects found are most likely extremely absorbed AGN characterized by a column density NH~10^24cm^-2. Their redshift has been directly determined from the X-ray data, by interpreting the detected emission line as the 6.4 keV Fe line. The measured equivalent width of the X-ray line is, in all three cases, several keV. This pilot study demonstrates the success of our search method and implies that a large sample of XLEOs can be obtained from the public XMM-Newton data archive., Comment: 10 pages, 3 figures, accepted for publication in ApJ Letters

We present XMM-Newton data centered on one of the MUNICS Near Infrared Cluster Survey fields (S2F1) and we discuss the X-ray properties of the 6 X-ray emitting EROs found. For one of them we have already obtained the redshift using near-infrared spectroscopic data, while for the remaining 5 EROs the analysis is based on photometric redshifts. We find evidence for the presence of an X-ray obscured QSO in at least 5 out of the 6 X-ray emitting EROs. For these 5 objects we derive intrinsic (2-10 keV) luminosities in excess of 10^44 erg/s and intrinsic column densities higher than 10^22 cm^-2. These values have been obtained through a basic X-ray spectral analysis for the three brightest sources and through the analysis of the hardness ratios for the remaining two. All of these 5 X-ray emitting EROs appear extended in the optical/near-infrared bands indicating that the host galaxy emission dominates at these wavelengths. This suggests that the hosted AGNs are likely to be absorbed also in the optical/near-infrared bands: i.e. they are likely X-ray obscured possible type 2 QSOs. For the remaining ERO the presence of an AGN is suggested both by its high 0.5-2 keV luminosity (L(0.5-2 keV)~10^43 erg/s) and by its X-ray-to-optical flux ratio. In this case the quality of the present data prevents us from placing firm constraints on the AGN type hosted. Finally, the near-IR spectrum obtained for one of the 6 EROs classifies the host galaxy as an elliptical at z~1.7 with a stellar mass well in excess of 10^11 M_\odot. This result corroborates the possible link between the QSO activity and the formation of massive spheroids., Comment: Accepted for publication on A&A; 10 pages, 5 figures

This paper presents the X-ray spectroscopy of an X-ray selected sample of 25 radio-loud (RL) AGNs extracted from the XBSS sample. The main goal is to study the origin of the X-ray spectral differences usually observed between radio-loud and radio-quiet (RQ) AGNs. To this end, a comparison sample of 53 RQ AGNs has been also extracted from the same XBSS sample and studied together with the sample of RL AGNs. We have focused the analysis on the distribution of the X-ray spectral indices of the power-law component that models the large majority of the spectra in both samples. We find that the mean X-ray energy spectral index is very similar in the 2 samples and close to alpha_X~1. However, the intrinsic distribution of the spectral indices is significantly broader in the sample of RL AGNs. In order to investigate the origin of this difference, we have divided the RL AGNs into blazars and ``non-blazars'', on the basis of the available optical and radio information. We find strong evidence that the broad distribution observed in the RL AGN sample is mainly due to the presence of the blazars. Furthermore, within the blazar class we have found a link between the X-ray spectral index and the value of the radio-to-X-ray spectral index suggesting that the observed X-ray emission is directly connected to the emission of the relativistic jet. This trend is not observed among the ``non-blazars'' RL AGNs. This favours the hypothesis that, in these latter sources, the X-ray emission is not significantly influenced by the jet emission and it has probably an origin similar to the RQ AGNs. Overall, the results presented here indicate that the observed distribution of the X-ray spectral indices in a given sample of RL AGNs is strongly dependent on the amount of relativistic beaming present in the selected sources., Comment: 18 pages, 10 figures, accepted for publication in A&A

The Early Data Release of the Sloan Digital Sky Survey (SDSS) contains 150 Narrow-Line Seyfert 1 (NLS1) galaxies, most of them previously unknown. We present here the study of the X-ray emission from two of these active galaxies (SDSS J030639.57+000343.2 and SDSS J141519.50-003021.6), based upon XMM-Newton observations. The spectral and timing characteristics of the two sources are presented and compared against the typical properties of known NLS1 galaxies. We found that these two NLS1 are within the dispersion range of the typical values of this class of AGN, although with some interesting features that deserve further studies., Comment: 5 pages, 8 figures. Accepted for publication on A&A Main Journal

An enigmatic, small class of IR and X-ray luminous sources, named ``Composite'' starburst/Seyfert galaxies, has been defined from IRAS and RASS data. The objects have optical spectra dominated by the features of HII galaxies (plus, in some cases, weak Seyfert signatures) but X-ray luminosities higher than expected from starbursts and more typical of Seyfert nuclei. The true nature of this class of objects is still unknown. We present Chandra data of four of these galaxies that were obtained to investigate the nature of the X-ray source. The X-ray spectrum, the lack of any significant extended component, and the observed variability indicate that the AGN is the dominant component in the X-ray domain., Comment: 4 pages; 3 figure; proceedings of XLVIII Congresso della Societa' Astronomica Italiana, Milano, Italy 19-23 april 2004, to be published on MemSAIt; Eds. A. Wolter; G. Israel; F. Bacciotti

ABRIDGED. We present "The XMM-Newton Bright Serendipitous Survey", two flux-limited samples with flux limit fx ~7E-14 cgs in the 0.5-4.5 keV (BSS) and 4.5-7.5 keV (HBSS) energy band, respectively. After discussing the survey strategy, we present the basic data on a complete sample of 400 X-ray sources derived from the analysis of 237 XMM-Newton fields. The survey covers an area of 28.10 (25.17 for the HBSS) sq. deg. Up to now ~71% (~90%) of the sources have been spectroscopically identified making the BSS (HBSS) the sample with the highest number of identified XMM-Newton sources published so far. We find that: a) the optical counterpart in the majority (~90%) of cases has a magnitude brighter than the POSS II limit; b) the majority of the objects identified so far are broad line AGN. No obvious trend of the source spectra (as deduced from the Hardness Ratios analysis) as a function of the count rate is seen and the average spectra of the "extragalactic" population corresponds to an X-ray energy spectral index of ~0.8 (~0.64) for the BSS (HBSS) sample. About 13% (40%) of the sources are described by an energy spectral index flatter than that of the CXB. We measure a surface density of optically type 1 and type 2 AGN of 1.63+/-0.25 deg-2 and 0.83+/-0.18$ deg-2, respectively; optically type 2 AGN represent 34+/-9% of the total AGN population. Finally, we find a clear separation, in the hardness ratio diagram and in the (hardness ratio) vs. (X-ray to optical flux ratio) diagram, between "coronal emitting" stars and extragalactic sources., Comment: 42 pages, 7 figures, 8 Tables, Accepted for publication in A&A

We present here "The XMM-Newton Bright Serendipitous Survey", a survey program conducted by the XMM-Newton Survey Science Center. In particular we discuss the main goals of this project, we present the sample(s) and the current optical breakdown and we discuss some broad band spectral properties as derived from an hardness ratio analysis of the single sources. Finally we report the 4.5--7.5 keV Log(N$>$S)-LogS for type 1 and type 2 AGN., Comment: On Behalf of the XMM-Newton Survey Science Centre (SSC) Consortium, 6 pages, 3 figures, Presented at the 48th meeting of the Italian Astronomical Society, Milan, April 19-23, 2004. To appear in the Proceedings

We report the discovery of a Compton-thick AGN and of intense star-formation activity in the nucleus and disk, respectively, of the nearly edge-on superwind galaxy NGC 4666. Spatially unresolved emission is detected by BeppoSAX only at energies <10 keV, whereas spatially resolved emission from the whole disk is detected by XMM-Newton. A prominent (EW ~ 1-2 keV) emission line at ~6.4 keV is detected by both instruments. From the XMM-Newton data alone the line is spectrally localized at E ~ 6.42 +/- 0.03 keV, and seems to be spatially concentrated in the nuclear region of NGC 4666. This, together with the presence of a flat (Gamma ~ 1.3) continuum in the nuclear region, suggests the existence of a strongly absorbed (i.e., Compton-thick) AGN, whose intrinsic 2-10 keV luminosity is estimated to be L_{2-10} > 2 x 10^{41} erg/s. At energies <1 keV the integrated (BeppoSAX) spectrum is dominated by a ~0.25 keV thermal gas component distributed throughout the disk (resolved by XMM-Newton). At energies ~2-10 keV, the integrated spectrum is dominated by a steep (G > 2) power-law (PL) component. The latter emission is likely due to unresolved sources with luminosity L ~ 10^{38} - 10^{39} erg/s that are most likely accreting binaries (with BH masses <8 M_sun). Such binaries, which are known to dominate the X-ray point-source luminosity in nearby star-forming galaxies, have Gamma ~ 2 PL spectra in the relevant energy range. A Gamma ~ 1.8 PL contribution from Compton scattering of (the radio-emitting) relativistic electrons by the ambient FIR photons may add a truly diffuse component to the 2-10 keV emission., Comment: A&A, in press (10 pages, 14 figures.) Full gzipped psfile obtainable from http://www.bo.iasf.cnr.it/~malaguti/r_stuff.html

Based on recent work on spectral decomposition of the emission of star-forming galaxies, we assess whether the integrated 2-10 keV emission from high-mass X-ray binaries (HMXBs), L_{2-10}^{HMXB}, can be used as a reliable estimator of ongoing star formation rate (SFR). Using a sample of 46 local (z < 0.1) star forming galaxies, and spectral modeling of ASCA, BeppoSAX, and XMM-Newton data, we demonstrate the existence of a linear SFR-L_{2-10}^{HMXB} relation which holds over ~5 decades in X-ray luminosity and SFR. The total 2-10 keV luminosity is not a precise SFR indicator because at low SFR (i.e., in normal and moderately-starbursting galaxies) it is substantially affected by the emission of low-mass X-ray binaries, which do not trace the current SFR due to their long evolution lifetimes, while at very high SFR (i.e., for very luminous FIR-selected galaxies) it is frequently affected by the presence of strongly obscured AGNs. The availability of purely SB-powered galaxies - whose 2-10 keV emission is mainly due to HMXBs - allows us to properly calibrate the SFR-L_{2-10}^{HMXB} relation. The SFR-L_{2-10}^{HMXB} relation holds also for distant (z ~ 1) galaxies in the Hubble Deep Field North sample, for which we lack spectral information, but whose SFR can be estimated from deep radio data. If confirmed by more detailed observations, it may be possible to use the deduced relation to identify distant galaxies that are X-ray overluminous for their (independently estimated) SFR, and are therefore likely to hide strongly absorbed AGNs., Comment: Astronomy & Astrophysics, in press (15 pages, 7 figures, 4 tables)

We discuss XMM-Newton and BeppoSAX observations of MKN 231, the lowest-redshift Broad Absorption Line (BAL) QSO known so far and one of the best-studied Ultra Luminous Infrared Galaxies. By combining the XMM-Newton spectral resolution and the high-energy bandpass of BeppoSAX we have been able to study in more detail than previously possible its 0.2--50 keV spectral properties. The BeppoSAX PDS data unveiled, for the first time, a highly absorbed ($N_H\sim 2\times 10^{24}$cm$^{-2}$) power-law component. We find that: a) below 10 keV we are seeing only reprocessed radiation through reflection and/or scattering; b) the intrinsic 2-10 keV luminosity of MKN 231 is $1^{+1.0}_{-0.5} \times 10^{44}$ ergs s$^{-1}$, i.e. more than an order of magnitude greater than previous measurements; c) the starburst activity significantly contributes to the soft ($E<2$ keV) X-ray emission., Comment: 11 pages,3 figures, Latex manuscript, Accepted for publication in Astronomy and Astrophysics

XMM-Newton observations are presented for the z=0.83 cluster of galaxies MS1054-0321, the highest redshift cluster in the Einstein Extended Medium Sensitivity Survey (EMSS). The temperature inferred by the XMM-Newton data, T=7.2 (+0.7, -0.6) keV, is much lower than the temperature previously reported from ASCA data, T=12.3 (+3.1, -2.2) keV (Donahue et al. 1998), and a little lower than the Chandra temperature, T=10.4(+1.7, -1.5) keV, determined by Jeltema et al. 2001. The discrepancy between the newly derived temperature and the previously derived temperatures is discussed in detail. If one allows the column density to be a free parameter, then the best fit temperature becomes T=8.6 (+1.2, -1.1) keV, and the best fit column density becomes N_(H)=1.33 (+0.15 -0.14) x 10^20 atoms/cm^2. The iron line is well detected in the XMM-Newton spectrum with a value for the abundance of Z=0.33 (+0.19 -0.18) Zsol, in very good agreement with previous determinations. The derived XMM X-ray luminosity for the overall cluster in the 2-10 keV energy band is L_X=(3.81 +/- 0.19) x 10^44 h^-2 erg s^-1 while the bolometric luminosity is L_BOL=(8.05+/-0.40) x 10^44 h^-2 erg s^-1. The XMM-Newton data confirm the substructure in the cluster X-ray morphology already seen by ROSAT and in much more detail by Chandra. The central weak lensing clump is coincident with the main cluster component and has a temperature T=8.1 (+1.3, -1.2) keV. The western weak lensing clump coincides with the western X-ray component which is much cooler with a temperature T=5.6 (+0.8, -0.6)$ keV. Given the newly determined temperature, MS1054-0321 is no longer amongst the hottest clusters known., Comment: To appear in the A&A main Journal, 13 pages including 3 postscript figures and 4 tables. Figs. 1, 4, 5 and 7 are too large and are not given here. The whole paper as pdf file is posted at http://www.ira.cnr.it/~gioia/PUB/publications.html

This paper presents the analysis of a statistically complete sample of 28 serendipitous X-ray sources selected in 82 pointed XMM-Newton fields down to a count-rate of 0.002 counts s^-1(4.5-7.5 keV energy band). This is the first sample selected in this energy range to have complete spectroscopic identifications and redshift determinations for all the objects. Apart from one Galactic source (an interacting binary), all the objects are AGNs. Their optical and X-ray properties (derived from the spectral analysis of the XMM-EPIC data) are compared together. The good correlation between the optical spectral type and the X-ray absorption properties supports the AGN unified model. Only one object that does not fit the relation between optical and X-ray absorption is found, namely a Seyfert 1.9 with no evidence of obscuration in the X-ray band (NH<1.3x10^20 cm^-2). In total, 7 sources out of 27 are heavily obscured in the X-ray (NH>10^22 cm^-2), corresponding to a surface density of 0.7 deg^-2 at the flux limit the sample (4-7x10^-14 erg s^-1 cm^-2 in the 4.5-7.5 keV energy band). Among these obscured objects, two sources show a large (intrinsic) luminosity (L_[2-10keV]>10^44 erg s^-1) and are thus classified as type 2 QSO. Finally, we have compared the fraction of X-ray absorbed AGNs (26%) with that predicted by the current XRB synthesis models at the flux limit of the survey. We find that the models significantly (~90% confidence level) over predict the fraction of absorbed AGNs thus confirming also in this hard energy band (4.5-7.5 keV) similar results recently obtained in the 2-10 keV band., Comment: Accepted for publication in A&A

We present the preliminary results of an on-going near-IR low resolution spectroscopic follow-up of a complete sample of 30 bright (K'<18.5) EROs selected over 360 arcmin^2 from the MUNICH survey. Among the 13 EROs observed so far, 7 turned out to be early-type galaxies at 1.21., Comment: 2 pages, 1 figure. To appear in the proceedings of the Venice conference "Multiwavelength Mapping of Galaxy Formation and Evolution"

Here we present the results obtained from the analysis of 75 ksec of XMM-Newton observations of a sample of EROs selected from one MUNICS field (K'<19.5 mag). We find 6 EROs with a X-ray counterpart down to a 2--10 keV flux limit of ~10^{-15} cgs. For all of them the X-ray--to--optical flux ratios and the 2--10 keV luminosities suggest the presence of AGN. In particular, a complete X-ray spectral analysis shows that high luminosity, obscured AGNs (i.e. QSO2 candidates) are present in 3 of them., Comment: 2 pages, 1 figure. To appear in the proceedings of the Venice conference "Multiwavelength Mapping of Galaxy Formation and Evolution"

We present deep Chandra and XMM obervations of the galaxy cluster RDCS1252.9-2927, which was selected from the ROSAT Deep Cluster Survey (RDCS) and confirmed by extensive spectroscopy with the VLT at redshift z=1.237. With the Chandra data, the X-ray emission from the intra-cluster medium is well resolved and traced out to 500 kpc, thus allowing a measurement of the physical properties of the gas with unprecedented accuracy at this redshift. We detect a clear 6.7 keV Iron K line in the Chandra spectrum providing a redshift within 1% of the spectroscopic one. By augmenting our spectroscopic analysis with the XMM data (MOS detectors only), we significantly narrow down the 1 sigma error bar to 10% for the temperature and 30% for the metallicity, with best fit values kT = 6.0(+0.7,-0.5) keV, Z = 0.36(+0.12,-0.10) Z_sun. In the likely hypothesis of hydrostatic equilibrium, we measure a total mass of M_{500} = (1.9+-0.3)10^14 h_70^{-1}M_sun within R_{Delta=500} = 536 kpc. Overall, these observations imply that RDCS1252.9-2927 is the most X-ray luminous and likely the most massive bona-fide cluster discovered to date at z>1. When combined with current samples of distant clusters, these data lend further support to a mild evolution of the cluster scaling relations, as well the metallicity of the intra-cluster gas. Inspection of the cluster mass function in the current cosmological concordance model (h,Omega_m,Omega_Lambda)=(0.7,0.3,0.7) and sigma_8=0.7-0.8 shows that RDCS1252.9-2927 is an M* cluster at z=1.24, in keeping with number density expectations in the RDCS survey volume., Comment: 9 pages, 1 color figure (fig6.jpg). The Astronomical Journal in press (Jan 2004). Full resolution preprint available at http://www.eso.org/~prosati/RDCS1252/

We are carrying on a near-IR very low resolution spectroscopic follow-up in parallel with XMM-Newton observations of a complete sample of ~30 bright (K'<18.5) Extremely Red Objects (EROs) selected over an area of 360 arcmin^2 of the MUNICS survey. We here present the preliminary results of the spectroscopic and X-ray data analysis., Comment: 2 pages, "Multiwavelength Cosmology" Mykonos, June 2003, conference proceedings

We present an L-band spectrum of the Ultraluminous Infrared Galaxy IRAS 19254-7245 (the Superantennae), obtained with VLT-ISAAC. The high signal to noise ratio allows a study of the main spectral features with unprecedented detail for an extragalactic source. We argue that the main energy source in the IR is an obscured AGN. This is indicated by the low equivalent width of the 3.3 micron PAH feature, the broad absorption feature at 3.4 um, and the steep continuum at lambda>3.7 um (f_lambda ~lambda^(2.7)). The substructure of the 3.4 um absorption feature indicates that the absorption is due to hydrocarbon chains of 6-7 carbon atoms., Comment: 12 pages, 3 figures. ApJ Letters, in press

We present BeppoSAX and XMM-Newton observations of MKN 231. These observations and in particular the BeppoSAX PDS data allowed us to unveil, for the first time, the highly absorbed (N$_H\sim 2\times10^{24}$ cm$^{-2}$) AGN component. We find that: a) the AGN powering MKN231 has an intrinsic 2-10 keV luminosity of $1^{+1}_{-0.5}\times 10^{44}$ erg/s; b) the strong starburst activity contributes significantly in the 0.1-10 keV energy range. We propose that the starburst activity strongly contributes to the far infrared luminosity of MKN 231; this is also suggested by the multiwavelength properties of MKN 231., Comment: 4 pages, 2 fugures, Proc. of the meeting: "The Restless High-Energy Universe" (Amsterdam, The Netherlands), E.P.J. van den Heuvel, J.J.M. in 't Zand, and R.A.M.J. Wijers Eds

Recent BeppoSAX observations of Arp 299, a powerful far-IR merging starburst system composed of IC 694 and NGC 3690, clearly unveiled for the first time in this system the presence of a strongly absorbed active galactic nucleus (AGN). However the system was not spatially resolved by BeppoSAX. Here we present the analysis of archival Chandra and (for the first time) XMM-Newton observations, which allow us to disentangle the X-ray emission of the two galaxies. The detection of a strong 6.4 keV line in NGC 3690 clearly demonstrates the existence of an AGN in this galaxy, while the presence of a strong 6.7 keV Fe-Kalpha line in the spectrum of IC 694 suggests that also this nucleus might harbor an AGN. This would be the second discovery of two AGNs in a merging system after NGC 6240., Comment: 7 pages, 2 figures, Latex manuscript. Revised version after referee' comments; accepted for publication by ApJ (January 10, 2004)

We discuss the X-ray, optical and radio properties of AX J0843+2942, a high luminosity Type 2 AGN found in the ASCA Hard Serendipitous Survey. The X-ray spectrum is best described by an absorbed power-law model with photon index of Gamma = 1.72 (+0.3 -0.6) and intrinsic absorbing column density of NH = 1.44 (+0.33 -0.52) x 10E23 cm-2. The intrinsic luminosity in the 0.5-10 keV energy band is ~ 3x10E45 erg s-1, well within the range of quasar luminosities. AX J0843+2942, positionally coincident with the core of a triple and strong (S_1.4 GHz ~ 1 Jy; P_1.4 GHz ~ 9 x 10E33 erg s-1 Hz-1) radio source, is spectroscopically identified with a Narrow Line object (intrinsic FWHM of all the permitted emission lines <= 1200 km s-1) at z=0.398, having line features and ratios typical of Seyfert-2 like objects. The high X-ray luminosity, coupled with the high intrinsic absorption, the optical spectral properties and the radio power, allow us to propose AX J0843+2942 as a Radio-Loud "Type 2 QSO". A discussion of the SED of this object is presented here together with a comparison with the SED of Ultra Luminous Infrared Galaxies, other "Type 2 QSO" candidates from the literature, and "normal" Radio-Quiet and Radio-Loud QSOs., Comment: 10 pages, 7 figures, Latex manuscript, Accepted for publication in Ast ronomy and Astrophysics

XMM-Newton observations of 10 ULIRGs are reported. The aim is to investigate in hard X-rays a complete ULIRG sample selected from the bright IRAS 60$\mu$m catalogue. All sources are detected in X-rays, 5 of which for the first time. These observations confirm that ULIRGs are intrinsically faint X-rays sources, their observed X-ray luminosities being typically L(2-10 keV)<1E42-43 erg/s, whereas their bolometric luminosities are L>1E45 erg/s. In all sources we find evidence for thermal emission from hot plasma with kT~0.7keV, dominating the X-ray spectra below 1keV, and likely associated with a nuclear or circumnuclear starburst. This thermal emission appears uncorrelated with the FIR luminosity, suggesting that,in addition to the ongoing rate of star formation, other parameters may also affect it. The soft X-ray emission appears to be extended on a scale of ~30kpc for Mkn231 and IRAS19254-7245, possible evidence of galactic superwinds. In these 2 sources, in IRAS20551-4250 and IRAS23128-5919 we find evidence for the presence of hidden AGNs, while a minor AGN contribution may be suspected also in IRAS20100-4156. In particular, we have detected a strong Fe line at 6.4keV in the spectrum of IRAS19254-7245 and a weaker one in Mkn231, suggestive of deeply buried AGNs. For the other sources, the X-ray luminosities and spectral shapes are consistent with hot thermal plasma and X-ray binary emissions of mainly starburst origin. We find that the 2-10keV luminosities in these sources, most likely due to high-mass X-ray binaries, are correlated with L_FIR: both luminosities are good indicators of the current global SFR in the galaxy. The composite nature of ULIRGs is then confirmed, with hints for a predominance of the starburst over the AGN phenomenon in these objects., Comment: Accepted for publication on MNRAS; 16 pages, 7 figures

We have performed a detailed analysis of 3 optically normal galaxies extracted from the XMM Bright Serendipitous Source Sample. Thanks to the good statistics of the XMM-Newton data, we have unveiled the presence of an AGN in all of them. In particular, we detect both X-ray obscured (N_H>10^{22} cm^{-2}) and unobscured (N_H<10^{22} cm^{-2}) AGN with intrinsic 2--10 keV luminosities in the range between 10^{42} -- 10^{43} erg s^{-1}. We find that the X-ray and optical properties of the sources discussed here could be explained assuming a standard AGN hosted by galaxies with magnitudes M_R

An unbiased estimate of the average intrinsic X-ray properties and column density distribution of Seyfert galaxies in the local Universe is crucial to validate unified models of active galactic nuclei (AGNs) and to synthesis models for the X-ray background. We present here preliminary results obtained from an on-going XMM-Newton study (~250 ks awarded in the EPIC GT) on a well-defined, statistically complete, and significant sample of nearby Seyfert galaxies., Comment: 4 pages, 3 figures, to appear in "Carnegie Observatories Astrophysics Series, Vol. 1: Coevolution of Black Holes and Galaxies," ed. L. C. Ho (Pasadena: Carnegie Observatories, http://www.ociw.edu/ociw/symposia/series/symposium1/proceedings.html)'

We present the results obtained with BeppoSAX observations of the three Composite Seyfert/star-forming galaxies: IRAS 20051-1117, IRAS 04392-0123 and IRAS 01072+4954. These sources belong to an enigmatic class of X-ray sources detected in the ROSAT All-Sky Survey (Moran et al. 1996) which is composed of 6 low redshift galaxies. Their optical spectra are dominated by the features of HII galaxies while their X-ray luminosities (< 10^{42} ergs/s) are typical of Seyfert galaxies. IRAS 20051-1117 shows a 2-10 keV spectrum well described by a power-law with photon index = 1.9 and low intrinsic absorption. This result, the ratio Flux(2-10 keV)/Flux([OIII]) and the significant X-ray variability detected, clearly rule out a Compton thick nature of this source. IRAS 04392-0123 and IRAS 01072+4954, instead, have a BeppoSAX flux a factor of ~ 50-80 smaller than in the previous ROSAT observations, resulting in poor statistics, that prevents detailed modeling., Comment: 4 pages, 2 figures. To appear in "Carnegie Observatories Astrophysics Series, Vol. 1: Coevolution of Black Holes and Galaxies," ed. L. C. Ho (Pasadena: Carnegie Observatories, http://www.ociw.edu/ociw/symposia/series/symposium1/proceedings.html)