arXiv subjects

Fabrizio Fiore

Publications and source records attributed to Fabrizio Fiore.

At least 73 records · Page 4Linked to original sources

arXiv2011

Constraining Dynamical Dark Energy Models through the Abundance of High-Redshift Supermassive Black Holes

We compute the number density of massive Black Holes (BHs) at the centre of galaxies at z=6 in different Dynamical Dark Energy (DDE) cosmologies, and compare it with existing observational lower limits, to derive constraints on the evolution of the Dark Energy equation of state parameter w. Our approach only assumes the canonical scenario for structure formation from the collapse of overdense regions of the Dark Matter dominated primordial density field on progressively larger scales; the Black Hole accretion and merging rate have been maximized in the computation so as to obtain robust constraints on w and on its look-back time derivative w_a. Our results provide independent constraints complementary to those obtained by combining Supernovae, Cosmic Microwave Background and Baryonic Acoustic Oscillations; while the latter concern combinations of w_0 and w_a leaving the time evolution of the state parameter w_a highly unconstrained, the BH abundance mainly provide upper limits on w_a, only weakly depending on w_0. Combined with the existing constraints, our results significantly restrict the allowed region in DDE parameter space, ruling out DDE models not providing cosmic time and fast growth factor large enough to allow for the building up of the observed abundance of BHs; in particular, models with -1.2 \leq w_0 \leq -1 and positive redshift evolution w_a > 0.8 - completely consistent with previous constraints - are strongly disfavoured by our independent constraints from BH abundance. Such range of parameters corresponds to "Quintom" DDE models, with w crossing -1 starting from larger values.

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arXiv2011

Demography of high redshift AGN

High redshift AGN holds the key to understand the early structure formation and to probe the Universe during its infancy. We review the latest searches for high-z AGN in the deepest X-ray field so far, the Chandra Deep Field South (CDFS) 4 Msecond exposure. We do not confirm the positive detection of a signal in the stacked Chandra images at the position of z~6 galaxies recently reported by Treister and collaborators. We present z>3 X-ray sources number counts in the 0.5-2 keV band obtained joining CDFS faint detections with Chandra-COSMOS and XMM-COSMOS detections. We use these number counts to make predictions for surveys with three mission concepts: Athena, WFXT and a Super-Chandra.

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arXiv2011

The large-scale structure in the Chandra Deep Field South

We have studied the large scale distribution of matter in the Chandra Deep Field South on the basis of photometric redshifts and we have identifed several over-densities between redshift 0.6 and 2.3. We analyse two of these structures using the deepest X-ray observations ever obtained: 4 Ms with the Chandra satellite and 2.5 Ms with XMM-Newton. We set a very faint upper limit on the X-ray luminosity of a structure at redshift 1.6, and we find an extended X-ray emission from a structure at redshift 0.96 of which we can estimate the gas temperature and make a comparison with the scaling relations between the X-ray luminosity and mass or temperature of high redshift galaxy clusters.

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arXiv2010

Identification of (high-redshift) AGN with WFXT: lessons from COSMOS and CDFS

The Wide Field X-ray Telescope (WFXT) will provide tens of millions of AGN, with more than 4x10^5 expected at z>3. Here we review the issues present in the identification of (large) samples of faint and high-redshift X-ray sources, and describe a statistical, powerful tool that can be applied to WFXT catalogs. The depth of associated optical and near infrared catalogs, needed for a reliable and as much complete as possible identification, are also discussed, along with the combined synergies with existing or planned facilities

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arXiv2010

Quasar feedback revealed by giant molecular outflows

In the standard scenario for galaxy evolution young star-forming galaxies transform into red bulge-dominated spheroids, where star formation has been quenched. To explain such a transformation, a strong negative feedback generated by accretion onto a super-massive black hole is often invoked. The depletion of gas resulting from quasar-driven outflows should eventually stop star-formation in the host galaxy and lead the black hole to "suicide" for starvation. Direct observational evidence for a major quasar feedback onto the host galaxy is still missing, since outflows previously observed in quasars are generally associated with the ionized component of the gas, which only accounts for a minor fraction of the total gas content, and typically occurring in the central regions. We used the IRAM PdB Interferometer to observe CO(1-0) in Mrk 231, the closest QSO known. Thanks to the wide band we detect broad wings of the CO line, with velocities up to 750 km/s and spatially resolved on the kpc scale. Such broad CO wings trace a giant molecular outflow of about 700 MSun/yr, far larger than the ongoing star-formation rate (~200 MSun/yr) observed in the host galaxy. This wind will totally expel the cold gas reservoir in Mrk 231 in about 1e7 yrs, therefore halting the star-formation activity on the same timescale. The inferred kinetic energy in the molecular outflow is ~1.2e44 erg/s, corresponding to a few percent of the AGN bolometric luminosity, very close to the fraction expected by models ascribing quasar feedback to highly supersonic shocks generated by radiatively accelerated nuclear winds. The direct observational evidence for quasar feedback reported here provides solid support to the scenarios ascribing the observed properties of local massive galaxies to quasar-induced large scale winds.

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arXiv2010

Multiwavelength perspective of AGN evolution

Discovering and studying obscured AGN at z>1-3 is important not only to complete the AGN census, but also because they can pinpoint galaxies where nuclear accretion and star-formation are coeval, and mark the onset of AGN feedback. We present the latest results on the characterization of z=1-3 galaxies selected for their high mid-infrared to optical flux ratio, showing that they are massive and strongly star-forming galaxies, and that many do host highly obscured AGN. We present a pilot program to push the search of moderately obscured AGN up to z=5-6 and discuss the perspectives of this line of research.

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arXiv2010

The Building Up of the Black Hole Mass - Stellar Mass Relation

We derive the growth of SMBHs relative to the stellar content of their host galaxy predicted under the assumption of BH accretion triggered by galaxy encounters occurring during their merging histories. We show that, within this framework, the ratio Gamma=(M_BH/M_*)(z)/(M_BH/M_*)(z=0) between the Black Hole mass and the galactic stellar mass (normalized to the local value) depends on both BH mass and redshift. While the average value and the spread of Gamma(z) increase with z, such an effect is larger for massive BHs, reaching values Gamma=5 for massive Black Holes (M>10^9 M_{\odot}) at z>4, in agreement with recent observations of high-redshift QSOs; this is due to the effectiveness of interactions in triggering BH accretion in high-density environments at high redshifts. To test such a model against observations, we worked out specific predictions for sub-samples of the simulated galaxies corresponding to the different observational samples for which measurements of Gamma have been obtained. We found that for Broad Line AGNs at 1 4.

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arXiv2009

The Chandra COSMOS Survey, I: Overview and Point Source Catalog

The Chandra COSMOS Survey (C-COSMOS) is a large, 1.8 Ms, Chandra} program that has imaged the central 0.5 sq.deg of the COSMOS field (centered at 10h, +02deg) with an effective exposure of ~160ksec, and an outer 0.4sq.deg. area with an effective exposure of ~80ksec. The limiting source detection depths are 1.9e-16 erg cm(-2) s(-1) in the Soft (0.5-2 keV) band, 7.3e(-16) erg cm^-2 s^-1 in the Hard (2-10 keV) band, and 5.7e(-16) erg cm(-2) s(-1) in the Full (0.5-10 keV) band. Here we describe the strategy, design and execution of the C-COSMOS survey, and present the catalog of 1761 point sources detected at a probability of being spurious of <2e(-5) (1655 in the Full, 1340 in the Soft, and 1017 in the Hard bands). By using a grid of 36 heavily (~50%) overlapping pointing positions with the ACIS-I imager, a remarkably uniform (to 12%) exposure across the inner 0.5 sq.deg field was obtained, leading to a sharply defined lower flux limit. The widely different PSFs obtained in each exposure at each point in the field required a novel source detection method, because of the overlapping tiling strategy, which is described in a companion paper. (Puccetti et al. Paper II). This method produced reliable sources down to a 7-12 counts, as verified by the resulting logN-logS curve, with sub-arcsecond positions, enabling optical and infrared identifications of virtually all sources, as reported in a second companion paper (Civano et al. Paper III). The full catalog is described here in detail, and is available on-line.

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arXiv2009

How complex is the obscuration in AGN? New clues from the Suzaku monitoring of the X-ray absorbers in NGC7582

We present the results of a Suzaku monitoring campaign of the Seyfert 2 galaxy, NGC7582. The source is characterized by very rapid (on timescales even lower than a day) changes of the column density of an inner absorber, together with the presence of constant components arising as reprocessing from a Compton-thick material. The best fitting scenario implies important modifications to the zeroth order view of Unified Models. While the existence of a pc-scale torus is needed in order to produce a constant Compton reflection component and an iron K$α$ emission line, in this Seyfert 2 galaxy this is not viewed along the line of sight. On the other hand, the absorption of the primary continuum is due to another material, much closer to the BH, roughly at the distance of the BLR, which can produce the observed rapid spectral variability. On top of that, the constant presence of a $10^{22}$ cm$^{-2}$ column density can be ascribed to the presence of a dust lane, extended on a galactic scale, as previously confirmed by Chandra. There is now mounting evidence that complexity in the obscuration of AGN may be the rule rather than the exception. We therefore propose to modify the Unification Model, adding to the torus the presence of two further absorbers/emitters. Their combination along the line of sight can reproduce all the observed phenomenology.

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arXiv2008

Simbol-X: A Formation Flight Mission with an Unprecedented Imaging Capability in the 0.5-80 Kev Energy Band

The discovery of X-ray emission from cosmic sources in the 1960s has opened a new powerful observing window on the Universe. In fact, the exploration of the X-ray sky during the 70s-90s has established X-ray astronomy as a fundamental field of astrophysics. Today, the emission from astrophysical sources is by large best known at energies below 10 keV. The main reason for this situation is purely technical since grazing incidence reflection has so far been limited to the soft X-ray band. Above 10 keV all the observations have been obtained with collimated detectors or coded mask instruments. To make a leap step forward in X-ray astronomy above 10 keV it is necessary to extend the principle of focusing X ray optics to higher energies, up to 80 keV and beyond. To this end, ASI and CNES are presently studying the implementation of a X-ray mission called Simbol-X. Taking advantage of emerging technology in mirror manufacturing and spacecraft formation flying, Simbol-X will push grazing incidence imaging up to 80 keV and beyond, providing a strong improvement both in sensitivity and angular resolution compared to all instruments that have operated so far above 10 keV. This technological breakthrough will open a new high-energy window in astrophysics and cosmology. Here we will address the problematic of the development for such a distributed and deformable instrument. We will focus on the main performances of the telescope, like angular resolution, sensitivity and source localization. We will also describe the specificity of the calibration aspects of the payload distributed over two satellites and therefore in a not "frozen" configuration.

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arXiv2008

The metamorphosis of Supernova SN2008D/XRF080109: a link between Supernovae and GRBs/Hypernovae

The only supernovae (SNe) to have shown early gamma-ray or X-ray emission thus far are overenergetic, broad-lined Type Ic SNe (Hypernovae - HNe). Recently, SN 2008D shows several novel features: (i) weak XRF, (ii) an early, narrow optical peak, (iii) disappearance of the broad lines typical of SNIc HNe, (iv) development of He lines as in SNeIb. Detailed analysis shows that SN 2008D was not a normal SN: its explosion energy (KE ~ 6*10^{51} erg) and ejected mass (~7 Msun) are intermediate between normal SNeIbc and HNe. We derive that SN 2008D was originally a ~30Msun star. When it collapsed a black hole formed and a weak, mildly relativistic jet was produced, which caused the XRF. SN 2008D is probably among the weakest explosions that produce relativistic jets. Inner engine activity appears to be present whenever massive stars collapse to black holes.

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arXiv2008

Detecting Low-Mass Supermassive Black Holes

We demonstrate the feasibility of uncovering supermassive black holes in late-type, quiescent spiral galaxies by detecting signs of very low-level nuclear activity. We use a combination of x-ray selection and multi-wavelength follow-up. Here, we apply this technique to NGC 3184 and NGC 5457, both of type Scd, and show that strong arguments can be made that both host AGNs.

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arXiv2008

Finding Local Low-mass Supermassive Black Holes

The low-mass end of the supermassive black hole mass function is unknown and difficult to determine. Here we discuss our successful program to find active nuclei of late type "normal" galaxies using X-ray detections and multiwavelength identifications. We conclude that most of the Chandra detected nuclear X-ray sources are AGNs. We then outline methods of black hole mass determination when broad emission lines are unobservable.

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arXiv2008

Low-Level Nuclear Activity in Nearby Spiral Galaxies

We are conducting a search for supermassive black holes (SMBHs) with masses below 10^7 M_sun by looking for signs of extremely low-level nuclear activity in nearby galaxies that are not known to be AGNs. Our survey has the following characteristics: (a) X-ray selection using the Chandra X-ray Observatory, since x-rays are a ubiquitous feature of AGNs; (b) Emphasis on late-type spiral and dwarf galaxies, as the galaxies most likely to have low-mass SMBHs; (c) Use of multiwavelength data to verify the source is an AGN; and (d) Use of the highest angular resolution available for observations in x-rays and other bands, to separate nuclear from off-nuclear sources and to minimize contamination by host galaxy light. Here we show the feasibility of this technique to find AGNs by applying it to six nearby, face-on spiral galaxies (NGC 3169, NGC 3184, NGC 4102, NGC 4647, NGC 4713, NGC 5457) for which data already exist in the Chandra archive. All six show nuclear x-ray sources. The data as they exist at present are ambiguous regarding the nature of the nuclear x-ray sources in NGC 4713 and NGC 4647. We conclude, in accord with previous studies, that NGC 3169 and NGC 4102 are almost certainly AGNs. Most interestingly, a strong argument can be made that NGC 3184 and NGC 5457, both of type Scd, host AGNs.

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arXiv2008

The candidate filament close to the 3C295 galaxy cluster: optical and X-ray spectroscopy

We present a detailed analysis of the overdensity of X-ray sources colse to the 3C 295 galaxy cluster (z=0.46) to assess whether it is associated with a filament of the large-scale structure of the Universe. We obtained optical spectra of the optical counterparts of eleven sources associated with the filament, finding that one is at z=0.474. This is a type 1 AGN at 1.5 arcmin from the cluster center. We found three more sources with a redshift in the range 0.37 - 0.53. We extracted the stacked X-ray spectrum of 47 X-ray sources belonging to the putative filament. We found a significant narrow (at the resolution of the Chandra ACIS-I) line at E ~ 4.4 keV, the energy of the iron Kalpha line at the redshift of the cluster. The detection of this line is confirmed at a confidence level of better than 3sigma and its energy is constrained to be in the range 6.2--6.47 (at a 90% confidence level), excluding an identification with the 6.7 helium-like iron line from the hot cluster ICM at better than 4 sigma. We conclude that the detection of the redshifted line is a strong indication that at least several of the excess sources lie at z ~ 0.46 and that AGNs are efficient tracers of the ``filament'' connected with the central cluster of galaxies.

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arXiv2007

The cosmic X-ray background and the population of the most heavily obscured AGNs

We report on an accurate measurement of the CXB in the 15-50 keV range performed with the Phoswich Detection System (PDS) instrument aboard the BeppoSAX satellite. We establish that the most likely CXB intensity level at its emission peak (26-28 keV) is ~40 keV/cm2/s/sr, a value consistent with that derived from the best available CXB measurement obtained over 25 years ago with the first High Energy Astronomical Observatory satellite mission (HEAO-1; Gruber et al. 1999), whose intensity, lying well below the extrapolation of some lower energy measurements performed with focusing telescopes, was questioned in the recent years. We find that 90% of the acceptable solutions of our best fit model to the PDS data give a 20-50 keV CXB flux lower than 6.5E-08 erg/cm2/s/sr, which is 12% higher than that quoted by Gruber et al. (1999) when we use our best calibration scale. This scale gives a 20-50 keV flux of the Crab Nebula of 9.22E-09 erg/cm2/s, which is in excellent agreement with the most recent Crab Nebula measurements and 6% smaller than that assumed by Gruber et al. (1999). In combination with the CXB synthesis models we infer that about 25% of the intensity at ~30 keV arises from extremely obscured, Compton thick AGNs (absorbing column density N_H > 1.0E+24 H/cm2), while a much larger population would be implied by the highest intensity estimates. We also infer a mass density of supermassive BHs of ~3.0E+05 Msol/Mpc3. The summed contribution of resolved sources (Moretti et al. 2003) in the 2-10 keV band exceeds our best fit CXB intensity extrapolated to lower energies, but it is within our upper limit, so that any significant contribution to the CXB from sources other than AGNs, such as star forming galaxies and diffuse Warm-Hot Intergalactic Medium (WHIM), is expected to be mainly confined below a few keV.

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arXiv2006

The XMM-Newton wide-field survey in the COSMOS field: V. Angular Clustering of the X-ray Point Sources

We present the first results of the measurements of angular auto-correlation functions (ACFs) of X-ray point sources detected in the XMM-Newton observations of the 2 deg2 COSMOS field (XMM-COSMOS). A significant positive signals have been detected in the 0.5-2 (SFT) band, in the angle range of 0.5-24 arcminutes, while the positive signals were at the 2 and 3 sigma levels in the 2-4.5 (MED) and 4.5-10 (UHD) keV bands respectively. Correctly taking integral constraints into account is a major limitation in interpreting our results. With power-law fits to the ACFs without the integral constraint term, we find correlation lengths of theta_c=1.9+-0.3, 0.8+0.5-0.4 and 6+-2 arcseconds for the SFT, MED, and UHD bands respectively for gamma=1.8. The inferred comoving correlation lengths, also taking into account the bias by the source merging due to XMM-Newton PSF, are 9.8+-0.7, 5.8+1.4-1.7 and 12+-2 h-1 Mpc at the effective redshifts of 1.1, 0.9, and 0.6 for the SFT, MED, and UHD bands respectively. If we include the integral constraint term in the fitting process,assuming that the power-law extends to the scale length of the entire XMM-COSMOSfield, the correlation lengths become larger by 20%-90%. Comparing the inferred rms fluctuations of the spatial distribution of AGNs with those of the underlying mass, the bias parameters of the X-ray source clustering at these effective redshifts are in the range b(AGN)=1.5-4. (Edited to simple ascii.)

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arXiv2005

Probing the Local Group Medium Toward Mkn 421 with Chandra and FUSE

We report the detection of highly-ionized gas at z~0 seen in resonant UV and X-ray absorption lines toward the z=0.03 blazar Mkn 421. A total of 13 X-ray and 3 UV lines were measured (or upper limits derived), including three lines in the OVII K-series and Kαtransitions from neon, carbon, and nitrogen. From the three OVII lines we derive a 2σDoppler parameter constraint of 24<b<55 km/s. The FUSE spectrum shows strong Galactic low--velocity OVI 1032A absorption as well as a possible weak OVI high-velocity component (HVC). The Doppler parameter of the low-velocity OVI measured with FUSE is ~3σhigher than that derived from the OVII line ratios, indicating that the OVII and Galactic OVI arise in different phases. This velocity dispersion, along with limits on the gas temperature and density from the X-ray line ratios (assuming a single phase with collisional ionization equilibrium plus photoionization) are all consistent with an extragalactic absorber. However, the OVII Doppler parameter is inconsistent with the high temperature required to produce the observed OVI_HVC/OVII ratio, implying that the HVC is probably not related to the OVII. In addition, the OVI_Kαline detected by Chandra implies a column density ~4 times higher than the 1032A absorption. Although an extragalactic absorber is fully consistent with the measured column density ratios, a Galactic origin cannot be ruled out given the uncertainties in the available data.

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