We present an XMM-Newton time-resolved spectral analysis of the narrow-line Seyfert 1 galaxy Mrk 766. We analysed eight available observations taken between May 2000 and June 2005 with the EPIC-pn ...camera in order to investigate the X-ray spectral variability produced by changes in the mass accretion rate. The 0.2 − 10 keV spectra are extracted in time bins longer than 3 ks to have at least 3 × 104 net counts in each bin and then accurately trace the variations of the best-fit parameters of our adopted Comptonization spectral model. We tested a bulk-motion Comptonization (BMC) model which is in general applicable to any physical system powered by accretion onto a compact object, and assumes that soft seed photons are efficiently up-scattered via inverse Compton scattering in a hot and dense electron corona. The Comptonized spectrum has a characteristic power law shape, whose slope was found to increase for large values of the normalization of the seed component, which is proportional to the mass accretion rate ṁ (in Eddington units). Our baseline spectral model also includes a warm absorber lying on the line of sight and radiation reprocessing from the accretion disc or from outflowing matter in proximity to the central compact object. Our study reveals that the normalization-slope correlation, observed in Galactic black hole sources (GBHs), also holds for Mrk 766: variations of the photon index in the range Γ ~ 1.9−2.4 are indeed likely to be related to the variations of ṁ, as observed in X-ray binary systems. We finally applied a scaling technique based on the observed correlation to estimate the BH mass in Mrk 766. This technique is commonly and successfully applied to measure masses of GBHs, and this is the first time it has been applied in detail to estimate the BH mass in an AGN. We obtained a value of MBH = 1.26-0.77+1.00×106 M⊙, which is in very good agreement with that estimated by the reverberation mapping.
The black hole-and-galaxy (BH-galaxy) co-evolution paradigm predicts a phase where most of the star formation (SF) and BH accretion takes place in gas-rich environments, namely, in what are likely to ...be very obscured conditions. In the first phase of this growth, some of the galactic gas is funnelled toward the centre of the galaxy and is accreted into the supermassive BH, triggering active galactic nucleus (AGN) activity. The large quantity of gas and dust hides the emission and the AGN appears as an obscured (type 2) AGN. The degree of obscuration in type 2 AGNs may even reach values as high as N H > 10 24 cm −2 (i.e., Compton-thick, CT). Population synthesis models of the X-ray background (XRB) suggest that a large population of CT-AGN is, in fact, needed to explain the still unresolved XRB emission at energy above 20 keV. In this work, we investigated the properties of 94 Ne V 3426 Å-selected type 2 AGN in COSMOS at z = 0.6 − 1.2, performing optical-to-far-infrared (FIR) spectral energy distribution (SED) fitting of COSMOS2020 photometric data to estimate the AGN bolometric luminosity and stellar mass, star formation rate, age of the oldest stars, and molecular gas mass for their host-galaxy. In addition, we performed an X-ray spectral analysis of the 36 X-ray-detected sources to obtain reliable values of the AGN obscuration and intrinsic luminosity, as well as to constrain the AGN properties of the X-ray-undetected sources. We found that more than two-thirds of our sample is composed of very obscured sources ( N H > 10 23 cm −2 ), with about 20% of the sources being candidate CT-AGN and half being AGNs in a strong phase of accretion ( λ Edd > 0.1). We built a mass- and redshift-matched control sample and its comparison with the Ne V sample indicates that the latter has a higher fraction of sources within the main sequence of star-forming galaxies and shows little evidence for AGNs quenching the SF. As the two samples have similar amounts of cold gas available to fuel the SF, this difference points towards a higher efficiency in forming stars in the Ne V -selected sample. The comparison with the prediction from the in situ co-evolution model suggests that Ne V is an effective tool for selecting galaxies in the obscured growth phase of the BH-galaxy co-evolution paradigm. We find that the “quenching phase” is still to come for most of the sample and only few galaxies show evidence of quenched SF activity.
In this paper, we release accurate photometric redshifts for 1692 counterparts to Chandra sources in the central square degree of the Cosmic Evolution Survey (COSMOS) field. The availability of a ...large training set of spectroscopic redshifts that extends to faint magnitudes enabled photometric redshifts comparable to the highest quality results presently available for normal galaxies. We demonstrate that morphologically extended, faint X-ray sources without optical variability are more accurately described by a library of normal galaxies (corrected for emission lines) than by active galactic nucleus (AGN) dominated templates, even if these sources have AGN-like X-ray luminosities. Preselecting the library on the bases of the source properties allowed us to reach an accuracy with a fraction of outliers of 5.8% for the entire Chandra-COSMOS sample. In addition, we release revised photometric redshifts for the 1735 optical counterparts of the XMM-detected sources over the entire 2 deg2 of COSMOS. For 248 sources, our updated photometric redshift differs from the previous release by Delta *Dz > 0.2. These changes are predominantly due to the inclusion of newly available deep H-band photometry (H AB = 24 mag). We illustrate once again the importance of a spectroscopic training sample and how an assumption about the nature of a source together, with the number and the depth of the available bands, influences the accuracy of the photometric redshifts determined for AGN. These considerations should be kept in mind when defining the observational strategies of upcoming large surveys targeting AGNs, such as eROSITA at X-ray energies and the Australian Square Kilometre Array Pathfinder Evolutionary Map of the Universe in the radio band.
We present the X-ray analysis of 30 luminous quasars at z ≃ 3.0 − 3.3 with pointed XMM–Newton observations (28–48 ks) originally obtained by our group to test the suitability of active galactic ...nuclei as standard candles for cosmological studies. The sample was selected in the optical from the Sloan Digital Sky Survey Data Release 7 to be representative of the most luminous, intrinsically blue quasar population, and by construction boasts a high degree of homogeneity in terms of optical and UV properties. In the X-rays, only four sources are too faint for a detailed spectral analysis, one of which is formally undetected. Neglecting one more object later found to be radio-loud, the other 25 quasars are, as a whole, the most X-ray luminous ever observed, with rest-frame 2–10 keV luminosities of 0.5 − 7 × 1045 erg s−1. The continuum photon index distribution, centred at Γ ∼ 1.85, is in excellent agreement with those in place at lower redshift, luminosity, and black-hole mass, confirming the universal nature of the X-ray emission mechanism in quasars. Even so, when compared against the well-known LX–LUV correlation, our quasars show an unexpectedly varied behaviour, splitting into two distinct subsets. About two-thirds of the sources are clustered around the relation with a minimal scatter of 0.1 dex, while the remaining one-third appear to be X-ray underluminous by factors of > 3−10. Such a large incidence (≈25%) of X-ray weakness has never been reported in radio-quiet, non-broad absorption line (BAL) quasar samples. Several factors could contribute to enhancing the X-ray weakness fraction among our z ≃ 3 blue quasars, including variability, mild X-ray obscuration, contamination from weak-line quasars, and missed BALs. However, the X-ray weak objects also have, on average, flatter spectra, with no clear evidence of absorption. Indeed, column densities in excess of a few ×1022 cm−2 can be ruled out for most of the sample. We suggest that, at least in some of our X-ray weak quasars, the corona might experience a radiatively inefficient phase due to the presence of a powerful accretion-disc wind, which substantially reduces the accretion rate through the inner disc and therefore also the availability of seed photons for Compton up-scattering. The origin of the deviations from the LX–LUV relation will be further investigated in a series of future studies.
Aim. According to coevolutionary scenarios, nuclear activity and star formation play relevant roles in the early stages of galaxy formation. We aim at identifying them in high-redshift galaxies by ...exploiting high-resolution and high-sensitivity X-ray and millimeter-wavelength data to confirm the presence or absence of star formation and nuclear activity and describe their relative roles in shaping the spectral energy distributions and in contributing to the energy budgets of the galaxies. Methods. We present the data, model, and analysis in the X-ray and millimeter (mm) bands for two strongly lensed galaxies, SDP.9 (HATLAS J090740.0-004200) and SDP.11 (HATLAS J091043.1-000322), which we selected in the Herschel-ATLAS catalogs for their excess emission in the mid-IR regime at redshift ≳1.5. This emission suggests nuclear activity in the early stages of galaxy formation. We observed both of them with Chandra ACIS-S in the X-ray regime and analyzed the high-resolution mm data that are available in the ALMA Science Archive for SDP.9. By combining the information available in mm, optical, and X-ray bands, we reconstructed the source morphology. Results. Both targets were detected in the X-ray, which strongly indicates highly obscured nuclear activity. ALMA observations for SDP.9 for the continuum and CO(6-5) spectral line with high resolution (0.02 arcsec corresponding to ~65 pc at the distance of the galaxy) allowed us to estimate the lensed galaxy redshift to a better accuracy than pre-ALMA estimates (1.5753 ± 0.0003) and to model the emission of the optical, millimetric, and X-ray band for this galaxy. We demonstrate that the X-ray emission is generated in the nuclear environment, which strongly supports that this object has nuclear activity. On the basis of the X-ray data, we attempt an estimate of the black hole properties in these galaxies. Conclusions. By taking advantage of the lensing magnification, we identify weak nuclear activity associated with high-z galaxies with high star formation rates. This is useful to extend the investigation of the relationship between star formation and nuclear activity to two intrinsically less luminous high-z star-forming galaxies than was possible so far. Given our results for only two objects, they alone cannot constrain the evolutionary models, but provide us with interesting hints and set an observational path toward addressing the role of star formation and nuclear activity in forming galaxies.
We investigate, for the first time at z~3, the clustering properties of 189 Type 1 and 157 Type 2 X-ray active galactic nuclei (AGNs) of moderate luminosity (left angle bracketL sub(bol)right angle ...bracket = 10 super(45.3) erg s super(-1)), with photometric or spectroscopic redshifts in the range 2.2 < z < 6.8. This result requires a drop in the halo masses of Type 1 and 2 COSMOS AGNs at z ~ 3 compared to z lap 2 XMM-COSMOS AGNs with similar luminosities. A model which assumes that the AGNs activity is triggered by major mergers is quite successful in predicting both the low halo mass of COSMOS AGNs and the typical mass of luminous SDSS quasars at z~3, with the latter inhabiting more massive halos respect to moderate luminosity AGNs. Following our clustering measurements, we argue that this fast BH growth at z~3 in AGNs with moderate luminosity occurs in DMHs with typical mass of ~ 6x 10 super(12) h super(-1) M sub(middot in circle).
The X-ray luminosity function (XLF) of active galactic nuclei (AGN) offers a robust tool to study the evolution and the growth of the supermassive black-hole population over cosmic time. Owing to the ...limited area probed by X-ray surveys, optical surveys are routinely used to probe the accretion in the high-redshift Universe z ≥ 3. However, optical surveys may be incomplete because they are strongly affected by dust redenning. In this work we derive the XLF and its evolution at high redshifts ( z ≥ 3) using a large sample of AGN selected in different fields with various areas and depths covering a wide range of luminosities. Additionally, we put the tightest yet constraints on the absorption function in this redshift regime. In particular, we used more than 600 soft X-ray selected (0.5 − 2 keV) high- z sources in the Chandra deep fields, the Chandra COSMOS Legacy survey, and the XMM-XXL northern field. We derived the X-ray spectral properties for all sources via spectral fitting, using a consistent technique and model. To model the parametric form of the XLF and the absorption function, we used a Bayesian methodology, allowing us to correctly propagate the uncertainties for the observed X-ray properties of our sources and also the absorption effects. The evolution of XLF is in agreement with a pure density evolution model similar to what is witnessed at optical wavelengths, although a luminosity-dependent density evolution model cannot be securely ruled out. A large fraction (∼60%) of our sources are absorbed by column densities of N H ≥ 10 23 cm −2 , while ∼17% of the sources are Compton-Thick. Our results favour a scenario where both the interstellar medium of the host and the AGN torus contribute to the obscuration. The derived black hole accretion rate density is roughly in agreement with the large-scale cosmological hydrodynamical simulations, if one takes into account the results that the X-ray AGN are hosted by massive galaxies, while it differs from that derived using JWST data. The latter could be due to the differences in the AGN and host-galaxy properties.
Context. In this work, we test feedback propagation models on the test case of 2MASS 0918+2117 (2M0918), a z = 0.149 X-ray variable AGN that shows tentative evidence for nuclear ultra-fast outflows ...(UFOs) in a 2005 XMM-Newton observation. We also investigate whether UFOs can be related to the observed X-ray variability. Aims. We observed 2M0918 with XMM-Newton and NuSTAR in 2020 to confirm the presence of and characterize the UFOs. We performed a kinematic analysis of the publicly available 2005 SDSS optical spectrum to reveal and measure the properties of galaxy-scale ionized outflows. Furthermore, we constructed 20-year-long light curves of observed flux, line-of-sight column density, and intrinsic accretion rate from the spectra of the first four SRG/eROSITA all-sky surveys and archival observations from Chandra and XMM-Newton . Methods. We detect UFOs with v ∼ 0.16 c and galaxy-scale ionized outflows with velocities of ∼700 km s −1 . We also find that the drastic X-ray variability (factors > 10) can be explained in terms of variable obscuration and variable intrinsic luminosity. Results. Comparing the energetics of the two outflow phases, 2M0918 is consistent with momentum-driven wind propagation. 2M0918 expands the sample of AGN with both UFOs and ionized gas winds from 5 to 6 and brings the sample of AGN hosting multiscale outflows to 19, contributing to a clearer picture of feedback physics. From the variations in accretion rate, column density, and ionization level of the obscuring medium, we propose a scenario that connects obscurers, an accretion enhancement, and the emergence of UFOs.
Aims. We study the spectral properties of the unresolved cosmic X-ray background (CXRB) in the 1.5–7.0 keV energy band with the aim of providing an observational constraint on the statistical ...properties of those sources that are too faint to be individually probed. Methods. We made use of the Swift X-ray observation of the Chandra deep field South complemented by the Chandra data. Exploiting the lowest instrument background (Swift) together with the deepest observation ever performed (Chandra) we measured the unresolved emission at the deepest level and with the best accuracy available today. Results. We find that the unresolved CXRB emission can be modeled by a single power law with a very hard photon index Γ = 0.1 ± 0.7 and a flux of 5-2.6+3.2 erg s-1 cm-2 deg-2 in the 2.0–10 keV energy band (1σ error). Thanks to the low instrument background of the Swift-XRT, we significantly improved the accuracy with respect to previous measurements. Conclusions. These results point towards a novel ingredient in AGN population synthesis models, namely a positive evolution of the Compton-thick AGN population from local Universe to high redshift.
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