F. Nicastro

Universidad Nacional Autónoma de México, Ciudad de México, The Federal District, Mexico

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Publications (200)659.12 Total impact

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    ABSTRACT: The backbone of the large-scale structure of the Universe is determined by processes on a cosmological scale and by the gravitational interaction of the dominant dark matter. However, the mobile baryon population shapes the appearance of these structures. Theory predicts that most of the baryons reside in vast unvirialized filamentary structures that connect galaxy groups and clusters, but the observational evidence is currently lacking. Because the majority of the baryons are supposed to exist in a large-scale, hot and dilute gaseous phase, X-rays provide the ideal tool to progress our understanding. Observations with the Athena+ X-ray Integral Field Unit will reveal the location, chemical composition, physical state and dynamics of the active population of baryons.
    06/2013;
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    ABSTRACT: This White Paper, submitted to the recent ESA call for science themes to define its future large missions, advocates the need for a transformational leap in our understanding of two key questions in astrophysics: 1) How does ordinary matter assemble into the large scale structures that we see today? 2) How do black holes grow and shape the Universe? Hot gas in clusters, groups and the intergalactic medium dominates the baryonic content of the local Universe. To understand the astrophysical processes responsible for the formation and assembly of these large structures, it is necessary to measure their physical properties and evolution. This requires spatially resolved X-ray spectroscopy with a factor 10 increase in both telescope throughput and spatial resolving power compared to currently planned facilities. Feedback from supermassive black holes is an essential ingredient in this process and in most galaxy evolution models, but it is not well understood. X-ray observations can uniquely reveal the mechanisms launching winds close to black holes and determine the coupling of the energy and matter flows on larger scales. Due to the effects of feedback, a complete understanding of galaxy evolution requires knowledge of the obscured growth of supermassive black holes through cosmic time, out to the redshifts where the first galaxies form. X-ray emission is the most reliable way to reveal accreting black holes, but deep survey speed must improve by a factor ~100 over current facilities to perform a full census into the early Universe. The Advanced Telescope for High Energy Astrophysics (Athena+) mission provides the necessary performance (e.g. angular resolution, spectral resolution, survey grasp) to address these questions and revolutionize our understanding of the Hot and Energetic Universe. These capabilities will also provide a powerful observatory to be used in all areas of astrophysics.
    06/2013;
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    ABSTRACT: We present the first results from our pilot 500 ks Chandra Low Energy Transmission Grating Large Program observation of the soft X-ray brightest source in the z 0.4 sky, the blazar 1ES 1553+113, aimed to secure the first uncontroversial detections of the missing baryons in the X-rays. We identify a total of 11 possible absorption lines, with single-line statistical significances between 2.2σ and 4.1σ. Six of these lines are detected at high single-line statistical significance (3.6 ≤ σ ≤ 4.1), while the remaining five are regarded as marginal detections in association with either other X-ray lines detected at higher significance and/or far-ultraviolet (FUV) signposts. Three of these lines are consistent with metal absorption at z 0, and we identify them with Galactic O I and C II. The remaining eight lines may be imprinted by intervening absorbers and are all consistent with being high-ionization counterparts of FUV H I and/or O VI intergalactic medium signposts. In particular, five of these eight possible intervening absorption lines (single-line statistical significances of 4.1σ, 4.1σ, 3.9σ, 3.8σ, and 2.7σ), are identified as C V and C VI Kα absorbers belonging to three WHIM systems at zX = 0.312, zX = 0.237, and zX = 0.133, which also produce broad H I (and O VI for the zX = 0.312 system) absorption in the FUV. For two of these systems (zX = 0.312 and 0.237), the Chandra X-ray data led the a posteriori discovery of physically consistent broad H I associations in the FUV (for the third system the opposite applies), so confirming the power of the X-ray-FUV synergy for WHIM studies. The true statistical significances of these three X-ray absorption systems, after properly accounting for the number of redshift trials, are 5.8σ (zX = 0.312; 6.3σ if the low-significance O V and C V Kβ associations are considered), 3.9σ (zX = 0.237), and 3.8σ (zX = 0.133), respectively.
    The Astrophysical Journal 05/2013; 769(2):90. · 6.73 Impact Factor
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    A. Gupta, S. Mathur, Y. Krongold, F. Nicastro
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    ABSTRACT: The Seyfert 1 galaxy Ark 564 was observed with Chandra high energy transmission gratings for 250 ks. We present the high resolution X-ray spectrum that shows several associated absorption lines. The photoionization model requires two warm absorbers with two different ionization states (logU=0.39\pm0.03 and logU=-0.99\pm0.13), both with moderate outflow velocities (~100 km s^-1) and relatively low line of sight column densities (logNH=20.94 and 20.11 cm^-2). The high ionization phase produces absorption lines of OVII, OVIII, NeIX, NeX, MgXI, FeXVII and FeXVIII while the low ionization phase produces lines at lower energies (OVI & OVII). The pressure--temperature equilibrium curve for the Ark 564 absorber does not have the typical "S" shape, even if the metallicity is super-solar; as a result the two warm-absorber phases do not appear to be in pressure balance. This suggests that the continuum incident on the absorbing gas is perhaps different from the observed continuum. We also estimated the mass outflow rate and the associated kinetic energy and find it to be at most 0.006% of the bolometric luminosity of Ark~564. Thus it is highly unlikely that these outflows provide significant feedback required by the galaxy formation models.
    The Astrophysical Journal 01/2013; 768(2). · 6.73 Impact Factor
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    A. Gupta, S. Mathur, Y. Krongold, F. Nicastro
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    ABSTRACT: We present \chandra high energy transmission grating spectra of the narrow-line Seyfert-1 galaxy Ark 564. The spectrum shows numerous absorption lines which are well modeled with low velocity outflow components usually observed in Seyfert galaxies \citep{Gupta2013}. There are, however, some residual absorption lines which are not accounted for by low-velocity outflows. Here we present identifications of the strongest lines as $K\alpha$ transitions of \oviin (two lines) and \ovin at outflow velocities of $\sim 0.1c$. These lines are detected at $6.9\sigma$, $6.2\sigma$, and $4.7\sigma$ respectively and cannot be due to chance statistical fluctuations. Photoionization models with ultra-high velocity components improves the spectral fit significantly, providing further support for the presence of relativistic outflow in this source. Without knowing the location of the absorber, its mass and energy outflow rates cannot be well constrained; we find $\dot{E}(outflow)/L_{bol}$ lower limit of $\geq 0.006$% assuming a bi-conical wind geometry. This is the first time that absorption lines with ultra-high velocities are unambiguously detected in the soft X-ray band. The presence of outflows with relativistic velocities in AGNs with Seyfert-type luminosities is hard to understand and provides valuable constraints to models of AGN outflows. Radiation pressure is unlikely to be the driving mechanism for such outflows and magneto-hydrodynamic may be involved.
    The Astrophysical Journal 01/2013; 772(1). · 6.73 Impact Factor
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    ABSTRACT: We present the X-ray spectral results from the longest X-ray multi-mirror mission-Newton observation, 133 ks, of the low luminosity active galactic nucleus NGC 7213. The hardness ratio analysis of the X-ray light curves discloses a rather constant X-ray spectral shape, at least for the observed exposure time, enabling us to perform X-ray spectral studies using the total observed spectrum. Apart from a neutral Fe K\alpha emission line, we also detect narrow emission lines from the ionised iron species, Fe xxv and Fe xxvi. Our analysis suggests that the neutral Fe K\alpha originates from a Compton-thin reflector, while the gas responsible for the high ionisation lines is collisionally excited. The overall spectrum, in the 0.3-10 keV energy band, registered by the European Photon Imaging Camera, can be modelled by a power-law component (with a slope of \Gamma\simeq1.9) plus two thermal components at 0.36 and 8.84 keV. The low-energy thermal component is entirely consistent with the X-ray spectral data obtained by the Reflection Grating Spectrometer between 0.35-1.8 keV.
    Monthly Notices of the Royal Astronomical Society 12/2012; 429(4). · 5.52 Impact Factor
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    ABSTRACT: We investigate the X-ray properties of three interacting luminous infrared galaxy systems. In one of these systems, IRAS 18329+5950, we resolve two separate sources. A second, IRAS 20550+1656, and third, IRAS 19354+4559, have only a single X-ray source detected. We compare the observed emission to PSF profiles and determine that three are extended in emission. One is compact, which is suggestive of an AGN, although all of our profiles have large uncertainties. We then model the spectra to determine soft (0.5--2 keV) and hard (2--10 keV) luminosities for the resolved sources and then compare these to relationships found in the literature between infrared and X-ray luminosities for starburst galaxies. We obtain luminosities of $\log(L_{\textrm{soft}}/\lsol) = 7.32,\:7.06,\:7.68$ and $\log(L_{\textrm{hard}}/\lsol) = 7.33,\: 7.07,\: 7.88$ for IRAS 18329+5950, IRAS 19354+4559, and IRAS 20550+1656, respectively. These are intermediate to two separate predictions in the literature for star-formation-dominated sources. Our highest quality spectrum of IRAS 20550+1656 suggests super-solar abundance of alpha elements at $2\sigma$ significance, with $\log(\frac{\alpha}{\alpha_{\odot}}) = [\alpha] = 0.4\pm0.2$. This is suggestive of recent enrichment with Type II supernovae, consistent with a starburst environment. The X-ray properties of the target galaxies are most likely due to starbursts, but we cannot conclusively rule out AGN.
    11/2012;
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    ABSTRACT: In this paper we investigate the power spectrum of the unresolved 0.5-2 keV cosmic X-ray background (CXB) with deep Chandra 4-Msec (Ms) observations in the Chandra Deep Field South (CDFS). We measured a signal that, on scales >30 arcsec, is significantly higher than the shot noise and is increasing with angular scale. We interpreted this signal as the joint contribution of clustered undetected sources like active galactic nuclei (AGN), galaxies and the intergalactic medium (IGM). The power of unresolved cosmic source fluctuations accounts for ˜12 per cent of the 0.5-2 keV extragalactic CXB. Overall, our modelling predicts that ˜20 per cent of the unresolved CXB flux is produced by low-luminosity AGN, ˜25 per cent by galaxies and ˜55 per cent by the IGM. We do not find any direct evidence of the so-called 'warm hot intergalactic medium' (i.e. matter with 105 < T < 107 K and density contrast δ < 1000), but we estimated that it could produce about 1/7 of the unresolved CXB. We placed an upper limit on the space density of postulated X-ray-emitting early black holes at z > 7.5 and compared it with supermassive black hole evolution models.
    Monthly Notices of the Royal Astronomical Society 11/2012; 427(1):651-663. · 5.52 Impact Factor
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    ABSTRACT: About 30-40 percent of the expected number of baryons is still missing in the local Universe (z \lesssim 0.4). They are predicted to be hiding in a web of intergalactic gas at temperatures of about 10^5-10^7 K (the WHIM). Detecting this matter has had limited success so far, because of its low-density and high temperature, which makes it difficult to detect with current far-ultraviolet and X-ray instrumentation. Here we present the first results from our pilot 500 ks Chandra-LETG observation of the soft X-ray brightest source in the z > 0.4 sky, the blazar 1ES 1553+113. We identify a total of 11 possible absorption lines, with single-line statistical significances between 2.2-4.1 sigma. Six of these lines are detected at high significance (3.6 < \sigma < 4.1), while the remaining five are regarded as marginal detections in association with either other X-ray lines detected at higher significance and/or FUV signposts. Three of these lines are consistent with metal absorption at z~0. The remaining 8 lines may be imprinted by intervening absorbers and are all consistent with being high-ionization counterparts of FUV HI and/or OVI IGM signposts. In particular, four of these eight absorption lines (4.1\sigma, 4.1\sigma, 3.8\sigma and 2.7\sigma), are identified as CV and CVI absorbers belonging to two WHIM systems at z_X = 0.312 and z_X = 0.133, which also produce broad HI and OVI absorption in the FUV. The true statistical significances of these two X-ray absorption systems, after properly accounting for the number of redshift trials, are 5.8\sigma and 3.8\sigma.
    10/2012;
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    ABSTRACT: Most of the baryons from galaxies have been "missing" and several studies have attempted to map the circumgalactic medium (CGM) of galaxies in their quest. Recent studies with the Hubble Space Telescope have shown that many galaxies contain a large reservoir of ionized gas with temperatures of about 10^5 K. Here we report on X-ray observations made with the Chandra X-ray Observatory probing an even hotter phase of the CGM of our Milky Way at about 10^6 K. We show that this phase of the CGM is massive, extending over a large region around the Milky Way, with a radius of over 100 kpc. The mass content of this phase is over ten billion solar masses, many times more than that in cooler gas phases and comparable to the total baryonic mass in the disk of the Galaxy. The missing mass of the Galaxy appears to be in this warm-hot gas phase.
    The Astrophysical Journal Letters 05/2012; 756(1). · 6.35 Impact Factor
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    ABSTRACT: We report a detection of an absorption line at ∼ 44. A in a > 500 ks Chandra HRC-S/LETG X-ray grating spectrum of the blazar H 2356-309. This line can be identified as intervening C V-Kα absorption, at z ≈ 0.112, produced by a warm (log T = 5.1 K) intergalactic absorber. The feature is significant at a 2.9σ level (accounting for the number of independent redshift trials). We estimate an equivalent hydrogen column density of log N H = 19.05 (Z/Z ⊙) −1 cm −2 . Unlike other previously reported FUV/X-ray metal detections of warm-hot intergalactic medium (WHIM), this CV absorber lies in a region with locally low galaxy density, at ∼ 2.2 Mpc from the closest galaxy at that redshift, and therefore is unlikely to be associated with an extended galactic halo. We instead tentatively iden-tify this absorber with an intervening Warm-Hot Intergalactic Medium filament possibly permeating a large–scale, 30 Mpc extended, structure of galaxies whose redshift centroid, within a cylinder of 7.5 Mpc radius centered on the line of sight to H 2356-309, is marginally consistent (at a 1.8 σ level) with the redshift of the absorber.
    The Astrophysical Journal 04/2012; 753(2). · 6.73 Impact Factor
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    ABSTRACT: In the past few years more and more pieces of evidence have been presented for a revision of the widely accepted Unified Model of Active Galactic Nuclei. A model based solely on orientation cannot explain all the observed phenomenology. In the following, we will present evidence that accretion rate is also a key parameter for the presence of Hidden Broad Line Regions in Seyfert 2 galaxies. Our sample consists of 21 sources with polarized Hidden Broad Lines and 18 sources without Hidden Broad Lines. We use stellar velocity dispersions from several studies on the CaII and Mg b triplets in Seyfert 2 galaxies, to estimate the mass of the central black holes via the Mbh-{\sigma}\ast relation. The ratio between the bolometric luminosity, derived from the intrinsic (i.e. unabsorbed) X-ray luminosity, and the Eddington luminosity is a measure of the rate at which matter accretes onto the central supermassive black hole. A separation between Compton-thin HBLR and non-HBLR sources is clear, both in accretion rate (log Lbol/LEdd = -1.9) and in luminosity (log Lbol = 43.90). When, properly luminosity-corrected, Compton-thick sources are included, the separation between HBLR and non-HBLR is less sharp but no HBLR source falls below the Eddington ratio threshold. We speculate that non-HBLR Compton-thick sources with accretion rate higher than the threshold, do possess a BLR, but something, probably related to their heavy absorption, is preventing us from observing it even in polarized light. Our results for Compton-thin sources support theoretical expectations. In a model presented by Nicastro (2000), the presence of broad emission lines is intrinsically connected with disk instabilities occuring in proximity of a transition radius, which is a function of the accretion rate, becoming smaller than the innermost stable orbit for very low accretion rates and therefore luminosities.
    The Astrophysical Journal 01/2012; 748(2). · 6.73 Impact Factor
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    ABSTRACT: Aims: We used data from the 58 month long, continuous Swift/Burst Alert Telescope (BAT) observations of the five brightest Seyfert galaxies at hard X-rays, to study their flux and spectral variability in the 20-100 keV energy band. The column density in these objects is less than 10^24 cm-2, which implies that the Swift/BAT data allow us to study the "true" variability of the central source. Results: All objects show significant variations, with an amplitude which is similar to the AGN variability amplitude at energies below 10 keV. We found evidence for an anti-correlation between variability amplitude and black hole mass. The light curves in both bands are well correlated, with no significant delays on time scales as short as 2 days. NGC 4151 and NGC 2110 do not show spectral variability, but we found a significant anti-correlation between hardness ratios and source flux in NGC 4388 (and NGC 4945, IC 4329, to a lesser extent). This "softer when brighter" behaviour is similar to what has been observed at energies below 10 keV, and cannot be explained if the continuum varies only in flux; the intrinsic shape should also steepen with increasing flux. Conclusions: The presence of significant flux variations indicate that the central source in these objects is intrinsically variable on time scales as short as 1-2 days. The intrinsic slope of the continuum varies with the flux (at least in NGC 4388). The positive "spectral slope-flux" correlation can be explained if the temperature of the hot corona decreases with increasing flux. The lack of spectral variations in two objects, could be due to the fact that they may operate in a different "state", as their accretion rate is less than 1% of the Eddington limit (significantly smaller than the rate of the other three objects in the sample).
    Astronomy and Astrophysics 08/2011; · 5.08 Impact Factor
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    ABSTRACT: We employ three-band Spitzer-MIPS observations to search for cold dust emission in three neutral hydrogen compact high-velocity clouds (CHVCs) in the vicinity of the Milky Way. Far-infrared emission correlated with HI column density was previously reported in HVC Complex C, indicating that this object contains dust heated by the Galactic radiation field at its distance of ~10kpc. Assuming published Spitzer, IRAS, and Planck IR-HI correlations for Complex C, our Spitzer observations are of sufficient depth to directly detect 160um dust emission in the CHVCs if it is present at the same level as in Complex C, but no emission is detected in any of the targets. For one of the targets (CHVC289) which has well-localized HI clumps, we therefore conclude that it is fundamentally different from Complex C, with either a lower dust-to-gas ratio or a greater distance from the Galactic disk (and consequently cooler dust temperature). Firm conclusions cannot be drawn for the other two Spitzer-observed CHVCs since their small-scale HI structures are not sufficiently well known; nonetheless, no extended dust emission is apparent despite their relatively high HI column densities. The lack of dust emission in CHVC289 suggests that at least some compact high-velocity clouds objects may exhibit very low dust-to-gas ratios and/or greater Galactocentric distances than large HVC complexes.
    The Astronomical Journal 08/2011; · 4.97 Impact Factor
  • 08/2011;
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    ABSTRACT: We assess the possibility of detecting the warm-hot intergalactic medium in emission and characterizing its physical conditions and spatial distribution through spatially resolved X-ray spectroscopy, in the framework of the recently proposed DIOS, EDGE, Xenia, and ORIGIN missions, all of which are equipped with microcalorimeter-based detectors. For this purpose, we analyze a large set of mock emission spectra, extracted from a cosmological hydrodynamical simulation. These mock X-ray spectra are searched for emission features showing both the O VII Kα triplet and O VIII Lyα line, which constitute a typical signature of the warm-hot gas. Our analysis shows that 1 Ms long exposures and energy resolution of 2.5 eV will allow us to detect about 400 such features per deg2 with a significance ≥5σ and reveals that these emission systems are typically associated with density ~100 above the mean. The temperature can be estimated from the line ratio with a precision of ~20%. The combined effect of contamination from other lines, variation in the level of the continuum, and degradation of the energy resolution reduces these estimates. Yet, with an energy resolution of 7 eV and all these effects taken into account, one still expects about 160 detections per deg2. These line systems are sufficient for tracing the spatial distribution of the line-emitting gas, which constitute an additional information, independent from line statistics, to constrain the poorly known cosmic chemical enrichment history and the stellar feedback processes.
    The Astrophysical Journal 05/2011; 734(2):91. · 6.73 Impact Factor
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    ABSTRACT: ORIGIN is a proposal for the M3 mission call of ESA aimed at the study of metal creation from the epoch of cosmic dawn. Using high-spectral resolution in the soft X-ray band, ORIGIN will be able to identify the physical conditions of all abundant elements between C and Ni to red-shifts of z=10, and beyond. The mission will answer questions such as: When were the first metals created? How does the cosmic metal content evolve? Where do most of the metals reside in the Universe? What is the role of metals in structure formation and evolution? To reach out to the early Universe ORIGIN will use Gamma-Ray Bursts (GRBs) to study their local environments in their host galaxies. This requires the capability to slew the satellite in less than a minute to the GRB location. By studying the chemical composition and properties of clusters of galaxies we can extend the range of exploration to lower redshifts (z ~ 0.2). For this task we need a high-resolution spectral imaging instrument with a large field of view. Using the same instrument, we can also study the so far only partially detected baryons in the Warm-Hot Intergalactic Medium (WHIM). The less dense part of the WHIM will be studied using absorption lines at low redshift in the spectra for GRBs.
    Experimental Astronomy 04/2011; 34(2):519. · 2.97 Impact Factor
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    ABSTRACT: We present the spectral results from a 130 ks observation, obtained from the X-ray Multi-Mirror Mission-Newton (XMM-Newton) observatory, of the type I Seyfert galaxy Fairall 9. An X-ray hardness-ratio analysis of the light-curves, reveals a `softer-when-brighter' behaviour which is typical for radio-quiet type I Seyfert galaxies. Moreover, we analyse the high spectral-resolution data of the reflection grating spectrometer and we did not find any significant evidence supporting the presence of warm-absorber in the low X-ray energy part of the source's spectrum. This means that the central nucleus of Fairall 9 is `clean' and thus its X-ray spectral properties probe directly the physical conditions of the central engine. The overall X-ray spectrum in the 0.5-10 keV energy-range, derived from the EPIC data, can be modelled by a relativistically blurred disc-reflection model. This spectral model yields for Fairall 9 an intermediate black-hole best-fit spin parameter of $\alpha=0.39^{+0.48}_{-0.30}$.
    Monthly Notices of the Royal Astronomical Society 03/2011; 415. · 5.52 Impact Factor
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    ABSTRACT: We present the first results of the spectroscopy of distant, obscured AGN as obtained with the ultra-deep (≈3.3 Ms) XMM-Newton survey in the Chandra deep field South. One of the primary goals of the project is to characterize the X-ray spectral properties of obscured and heavily obscured Compton-thick AGN over the range of redhifts and luminosities that are relevant in terms of their contribution to the X-ray background. The ultra-deep exposure, coupled with the XMM detector's spectral throughput, allowed us to accumulate good quality X-ray spectra for a large number of X-ray sources and, in particular, for heavily obscured AGN at cosmological redshifts. Specifically we present the X-ray spectral properties of two high-redshift - z = 1.53 and z = 3.70 - sources. The XMM spectra of both are very hard, with a strong iron Kα line at a rest-frame energy of ~6.4 keV. A reflection-dominated continuum provides the best description of the X-ray spectrum of the z = 1.53 source, while the intrinsic continuum of the z = 3.70 AGN is obscured by a large column NH ≈ 1024 cm-2 of cold gas. Compton-thick absorption, or close to it, is unambiguously detected in both sources. Interestingly, these sources would not be selected as candidate Compton thick AGN by some multiwavelength selection criteria based on the mid-infrared to optical and X-ray to optical flux ratios. This work is based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and the USA (NASA).Table 1 is only available in electronic form at http://www.aanda.org
    Astronomy and Astrophysics 02/2011; · 5.08 Impact Factor

Publication Stats

617 Citations
659.12 Total Impact Points

Institutions

  • 2004–2013
    • Universidad Nacional Autónoma de México
      • Institute of Astronomy
      Ciudad de México, The Federal District, Mexico
  • 2011–2012
    • Netherlands Institute for Space Research, Utrecht
      Utrecht, Utrecht, Netherlands
  • 2001–2012
    • Università Degli Studi Roma Tre
      • Department of Mathematics and Physics
      Roma, Latium, Italy
  • 1999–2012
    • Harvard-Smithsonian Center for Astrophysics
      • Smithsonian Astrophysical Observatory
      Cambridge, Massachusetts, United States
  • 1999–2009
    • The Astronomical Observatory of Brera
      Merate, Lombardy, Italy
  • 2005–2007
    • The Ohio State University
      • Department of Astronomy
      Columbus, Ohio, United States
  • 2000–2007
    • National Institute of Astrophysics
      • Institute of Space Astrophysics and Cosmic Physics IASF - Rome
      Roma, Latium, Italy