Comparison of the optical and X-ray obscuration in AGN
Resumen del trabajo presentado al XXIX XMM-Newton SSC consortium meeting, celebrado en Madrid (Es... more Resumen del trabajo presentado al XXIX XMM-Newton SSC consortium meeting, celebrado en Madrid (Espana) del 14 al 15 de marzo de 2016.
Testing the unified model of Active Galactic Nuclei in X-ray selected type 1 and type 2 quasars
Resumen del trabajo presentado al Symposium X-Ray Universe, celebrado en Dublin (Irlanda) del 16 ... more Resumen del trabajo presentado al Symposium X-Ray Universe, celebrado en Dublin (Irlanda) del 16 al 19 de junio de 2014.
To provide insight into the apparent mismatch between the optical and X-ray absorption properties... more To provide insight into the apparent mismatch between the optical and X-ray absorption properties observed in 10-30 % of Active Galactic Nuclei (AGN), we have conducted a detailed study of two X-ray unabsorbed AGN with a type-2 optical spectroscopic classification. In addition to high quality X-ray spectroscopic observations, that we used to determine both the AGN luminosities and absorption, we have a VLT/XSHOOTER UV-to-near-IR high resolution spectrum for each object, that we used to determine the AGN intrinsic emision corrected for both contamination from the AGN hosts and extinction. Our analysis has revealed that the apparent mismatch is provoked by galaxy dilution. We dilution of two AGN with extreme properties: one of them has an intrinsically very high Balmer decrement while the other lies in a galaxy more massive than expected.
Many different classes of X-ray sources contribute to the Galactic landscape at high energies. Al... more Many different classes of X-ray sources contribute to the Galactic landscape at high energies. Although the nature of the most luminous X-ray emitters is now fairly well understood, the population of low-to-medium X-ray luminosity (L X = 10 27−34 erg s −1) sources remains much less studied, our knowledge being mostly based on the observation of local members. The advent of wide field and high sensitivity X-ray telescopes such as XMM-Newton now offers the opportunity to observe this low-to-medium L X population at large distances. We report on the results of a Galactic plane survey conducted by the XMM-Newton Survey Science Centre (SSC). Beyond its astrophysical goals, this survey aims at gathering a representative sample of identified X-ray sources at low latitude that can be used later on to statistically identify the rest of the serendipitous sources discovered in the Milky Way. The survey is based on 26 XMM-Newton observations, obtained at |b| < 20 deg, distributed over a large range in Galactic longitudes and covering a summed area of 4 deg 2. The flux limit of our survey is 2 × 10 −15 erg cm −2 s −1 in the soft (0.5-2 keV) band and 1 × 10 −14 erg cm −2 s −1 in the hard (2-12 keV) band. We detect a total of 1319 individual X-ray sources. Using optical follow-up observations supplemented by crosscorrelation with a large range of multi-wavelength archival catalogues we identify 316 X-ray sources. This constitutes the largest group of spectroscopically identified low latitude X-ray sources at this flux level. The majority of the identified X-ray sources are active coronae with spectral types in the range AM at maximum distances of ∼1 kpc. The number of identified active stars increases towards late spectral types, reaching a maximum at K. Using infrared colours we classify 18% of the stars as giants. The observed distributions of F X /F V , X-ray and infrared colours indicates that our sample is dominated by a young (100 Myr) to intermediate (600 Myr) age population with a small contribution of close main sequence or evolved binaries. We find other interesting objects such as cataclysmic variables (d ∼ 0.6−2 kpc), low luminosity high mass stars (likely belonging to the class of γ-Cas-like systems, d ∼ 1.5−7 kpc), T Tauri and Herbig-Ae stars. A handful of extragalactic sources located in the highest Galactic latitude fields could be optically identified. For the 20 fields observed with the EPIC pn camera, we have constructed log N(>S) − log S curves in the soft and hard bands. In the soft band, the majority of the sources are positively identified with active coronae and the fraction of stars increases by about one order of magnitude from b = 60 • to b = 0 • at an X-ray flux of 2 × 10 −14 erg cm −2 s −1. The hard band is dominated by extragalactic sources, but there is a small contribution from a hard Galactic population formed by CVs, HMXB candidates or γ-Cas-like systems and by some active coronae that are also detected in the soft band. At b = 0 • the surface density of hard sources brighter than 1 × 10 −13 erg cm −2 s −1 steeply increases by one order of magnitude from l = 20 • to the Galactic centre region (l = 0.9 •).
Trabajo presentado al X-Ray Astronomy: 'Current challenges and New Frontiers in the Next Deca... more Trabajo presentado al X-Ray Astronomy: 'Current challenges and New Frontiers in the Next Decade', celebrado en Bologna (Italia) del 8 al 13 de septiembre de 2019.
Monthly Notices of the Royal Astronomical Society, 2021
We present a new, multimission catalogue of ultraluminous X-ray source (ULX) candidates, based on... more We present a new, multimission catalogue of ultraluminous X-ray source (ULX) candidates, based on recent data releases from each of the XMM–Newton, Swift, and Chandra observatories (the 4XMM-DR10, 2SXPS, and CSC2 catalogues, respectively). This has been compiled by cross-correlating each of these X-ray archives with a large sample of galaxies primarily drawn from the HyperLEDA archive. Significant efforts have been made to clean the sample of known non-ULX contaminants (e.g. foreground stars, background active galactic nuclei, supernovae), and also to identify ULX candidates that are common to the different X-ray catalogues utilized, allowing us to produce a combined ‘master’ list of unique sources. Our sample contains 1843 ULX candidates associated with 951 different host galaxies, making it the largest ULX catalogue compiled to date. Of these, 689 sources are catalogued as ULX candidates for the first time. Our primary motivation is to identify new sources of interest for detailed...
Monthly Notices of the Royal Astronomical Society, 2017
We present optical spectroscopy of candidate active galactic nuclei (AGN) pinpointed by a Swift f... more We present optical spectroscopy of candidate active galactic nuclei (AGN) pinpointed by a Swift follow-up campaign on unidentified transients in the XMM-Newton Slew Survey, increasing the completeness of the identifications of AGN in the Survey. Our Swift follow-up campaign identified 17 X-ray Telescope-detected candidate AGN, of which 9 were selected for optical follow-up and a further two were confirmed as AGN elsewhere. Using data obtained at the William Herschel Telescope, Very Large Telescope and New Technology Telescope, we find AGN features in seven of the candidates. We classify six as Seyfert types 1.0-1.5, with broad-line region velocities spanning 2000-12000 km s −1 , and identify one as a possible type II AGN, consistent with the lack of a soft band X-ray detection in the Slew Survey. The virial black hole mass estimates for the sample lie between 1× 10 8 and 3× 10 9 M , with one source likely emitting close to its Eddington rate, L Bol /L Edd ∼ 0.9. We find a wide redshift range 0.08 < z < 0.9 for the nine now confirmed AGN drawn from the unidentified Slew Survey sample. One source remaining unclassified shows outbursts rarely seen before in AGN. We conclude that AGN discovered in this way are consistent with the largely non-varying, Slew-selected, known AGN population. We also find parallels with XMM-Newton Bright Serendipitous Survey AGN selected from pointed observations, and postulate that shallow X-ray surveys select AGN drawn from the same populations that have been characterized in deeper X-ray-selected samples.
Monthly Notices of the Royal Astronomical Society, 2016
We study a sample of six X-ray-selected broad absorption line (BAL) quasi-stellar objects (QSOs) ... more We study a sample of six X-ray-selected broad absorption line (BAL) quasi-stellar objects (QSOs) from the XMM-Newton Wide Angle Survey. All six objects are classified as BALQSOs using the classic balnicity index, and together they form the largest sample of X-ray-selected BALQSOs. We find evidence for absorption in the X-ray spectra of all six objects. An ionized absorption model applied to an X-ray spectral shape that would be typical for non-BAL QSOs (a power law with energy index α = 0.98) provides acceptable fits to the X-ray spectra of all six objects. The optical to X-ray spectral indices, α OX , of the X-ray-selected BALQSOs, have a mean value of α OX = 1.69 ± 0.05, which is similar to that found for X-ray-selected and optically selected non-BAL QSOs of a similar ultraviolet luminosity. In contrast, optically selected BALQSOs typically have much larger α OX and so are characterized as being X-ray weak. The results imply that X-ray selection yields intrinsically X-ray bright BALQSOs, but their X-ray spectra are absorbed by a similar degree to that seen in optically selected BALQSO samples; X-ray absorption appears to be ubiquitous in BALQSOs, but X-ray weakness is not. We argue that BALQSOs sit at one end of a spectrum of X-ray absorption properties in QSOs related to the degree of ultraviolet absorption in C IV 1550 Å.
We present the distributions of the geometrical covering factors of the dusty tori (f 2) of activ... more We present the distributions of the geometrical covering factors of the dusty tori (f 2) of active galactic nuclei (AGNs) using an X-ray selected complete sample of 227 AGNs drawn from the Bright Ultra-hard XMM-Newton Survey. The AGNs have z from 0.05 to 1.7, 2-10 keV luminosities between 10 42 and 10 46 erg s −1 , and Comptonthin X-ray absorption. Employing data from UKIDSS, 2MASS, and the Wide-field Infrared Survey Explorer in a previous work, we determined the rest-frame 1-20 μm continuum emission from the torus, which we model here with the clumpy torus models of Nenkova et al. Optically classified type 1 and type 2 AGNs are intrinsically different, with type 2 AGNs having, on average, tori with higher f 2 than type 1 AGNs. Nevertheless, ∼20% of type 1 AGNs have tori with large covering factors, while ∼23%-28% of type 2 AGNs have tori with small covering factors. Low f 2 are preferred at high AGN luminosities, as postulated by simple receding torus models, although for type 2 AGNs the effect is certainly small. f 2 increases with the X-ray column density, which implies that dust extinction and X-ray absorption take place in material that share an overall geometry and most likely belong to the same structure, the putative torus. Based on our results, the viewing angle, AGN luminosity, and also f 2 determine the optical appearance of an AGN and control the shape of the rest-frame ∼1-20 μm nuclear continuum emission. Thus, the torus geometrical covering factor is a key ingredient of unification schemes.
Context. Our knowledge of the properties of AGN, especially those of optical type-2 objects, is v... more Context. Our knowledge of the properties of AGN, especially those of optical type-2 objects, is very incomplete. Because extragalactic source count distributions are dependent on the cosmological and statistical properties of AGN, they provide a direct method of investigating the underlying source populations. Aims. We aim to constrain 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. Methods. We have used 1129 XMM-Newton observations at |b| > 20 • covering a total sky area of 132.3 deg 2 to compile the largest complete samples of X-ray selected objects to date both in the 0.5−1 keV, 1−2 keV, 2−4.5 keV, 4.5−10 keV bands employed in standard XMM-Newton data processing and in the 0.5−2 keV and 2−10 keV energy bands more usually considered in source count studies. Our survey includes in excess of 30 000 sources and spans fluxes from ∼10 −15 to 10 −12 erg cm −2 s −1 below 2 keV and from ∼10 −14 to 10 −12 erg cm −2 s −1 above 2 keV where the bulk of the cosmic X-ray background energy density is produced. Results. The very large sample size we obtained means our results are not limited by cosmic variance or low counting statistics. A break in the source count distributions was detected in all energy bands except the 4.5−10 keV band. We find that an analytical model comprising 2 power-law components cannot adequately describe the curvature seen in the source count distributions. The shape of the log N(>S) − log S is strongly dependent on the energy band with a general steepening apparent as we move to higher energies. This is due to the fact that 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 −1 , 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.
Resumen del trabajo presentado al IV Meeting of AGN Research in Spain, celebrado en La Laguna, Te... more Resumen del trabajo presentado al IV Meeting of AGN Research in Spain, celebrado en La Laguna, Tenerife del 27 al 28 de octubre de 2016.
Context. Core extremely red quasars (core ERQ) have been proposed to represent an intermediate ev... more Context. Core extremely red quasars (core ERQ) have been proposed to represent an intermediate evolutionary phase in which a heavily obscured quasar blows out the circumnuclear interstellar medium with very energetic outflows before it becomes an optical quasar. Aims. We investigate whether the properties of core ERQ fit the AGN orientation-based unification scenario. Methods. We revised the general UV and optical emission line properties of core ERQ in the context of the orientation-based scenario. We used diagnostic diagrams based on UV emission line ratios and UV-to-optical line kinematic information to compare the physical and kinematic gas properties of core ERQ with those of other luminous narrow- and broad-line AGN. In particular, we provide a revised comparison of the [OIII] kinematics in 21 core ERQ (20 from Perrotta et al. 2019, MNRAS, 488, 4126 and SDSS J171420.38+414815.7, based on GTC EMIR near-infrared spectroscopy) with other samples of quasars with matching luminosit...
SDSS J110012.38+084616.3: A Compton-thick or X-ray weak AGN?
The space density of the most powerful absorbed AGN (QSO2) and their contribution to the AGN lumi... more The space density of the most powerful absorbed AGN (QSO2) and their contribution to the AGN luminosity output remains uncertain. Many of these objects are severely attenuated, so hard X-ray surveys alone do not fully prove the bulk of the obscured QSO population in the nearby Universe. We propose a 80 ksec XMM-Newton observation of an optically selected QSO2 at z~0.1. Comparing its [OIII] and 2-10 keV luminosities the source is likely a Compton-thick AGN. However, the X-ray spectral analysis seems to indicate that it might be instead Compton thin and X-ray weak. The proposed observations will allow us to unveil the true nature of this source and will give us key information on whether objects such as this are intrinsically different to the QSO2 population detected in hard X-ray surveys.
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Papers by Silvia Mateos