F. Civano, M. Elvis, G. Lanzuisi, K. Jahnke, G. Zamorani, L. Blecha, A. Bongiorno, M. Brusa, A. Comastri, H. Hao, A. Leauthaud, A. Loeb, M. Mignoli, V. Mainieri, E. Piconcelli, M. Salvato, N. Scoville, J. Trump, C. Vignali, T. Aldcroft, M. Bolzonella, E. Bressert, A. Finoguenov, A. Fruscione, A. M. Koekemoer, N. Cappelluti, F. Fiore, S. Giodini, R. Gilli, C. D. Impey, S. J. Lilly, E. Lusso, S. Puccetti, J. D. Silverman, H. Aussel, P. Capak, D. Frayer, E. Le Floc'h, H. J. McCracken, D. B. Sanders, D. Schiminovich, Y. Taniguchi
Feb 27, 2010·astro-ph.CO·PDF We present a detailed study of a peculiar source in the COSMOS survey at z=0.359. Source CXOCJ100043.1+020637 (CID-42) presents two compact optical sources embedded in the same galaxy. The distance between the 2, measured in the HST/ACS image, is 0.495" that, at the redshift of the source, corresponds to a projected separation of 2.46 kpc. A large (~1200 km/s) velocity offset between the narrow and broad components of Hbeta has been measured in three different optical spectra from the VLT/VIMOS and Magellan/IMACS instruments. CID-42 is also the only X-ray source having in its X-ray spectra a strong redshifted broad absorption iron line, and an iron emission line, drawing an inverted P-Cygni profile. The Chandra and XMM data show that the absorption line is variable in energy by 500 eV over 4 years and that the absorber has to be highly ionized, in order not to leave a signature in the soft X-ray spectrum. That these features occur in the same source is unlikely to be a coincidence. We envisage two possible explanations: (1) a gravitational wave recoiling black hole (BH), caught 1-10 Myr after merging, (2) a Type 1/ Type 2 system in the same galaxy where the Type 1 is recoiling due to slingshot effect produced by a triple BH system. The first possibility gives us a candidate gravitational waves recoiling BH with both spectroscopic and imaging signatures. In the second case, the X-ray absorption line can be explained as a BAL-like outflow from the foreground nucleus (a Type 2 AGN) at the rearer one (a Type 1 AGN), which illuminates the otherwise undetectable wind, giving us the first opportunity to show that fast winds are present in obscured AGN.
M. Dadina, M. Guainazzi, M. Cappi, S. Bianchi, C. Vignali, G. Malaguti, A. Comastri
The physical conditions of the gas forming the narrow line regions (NLR) in active galactic nuclei (AGN) have been extensively studied in the optical band. We take advantage of the spectacular extension ($\sim$15") of the NLR in the type II Seyfert galaxy NGC 5252 and of the complementary characteristics of $XMM$--$Newton$ and $Chandra$ to investigate the physical conditions of the gas in this galaxy. The X-ray data from $XMM$--$Newton$ are used to define the spectral properties of the ionising nuclear source. The $Chandra$ data are used to trace the spatial characteristics of the soft X-ray emission. This information is then compared to the HST characteristics. The X-ray spectrum of the nucleus of NGC 5252 is intrinsically flat and absorbed by neutral gas with a column density N~10$^{22}$ cm$^{-2}$. Below 1 keV a soft excess is detected. The high-resolution spectrum obtained with the XMM-Newton RGS shows the presence, in the 0.2-1.5 keV range, of emission lines which strongly indicate that the soft X-ray component is due to ionised gas. Moreover, the soft X-ray emission is spatially resolved around and well overlaps the images obtained in narrow [OIII] optical band. The [OIII]/soft-X flux ratios along the ionisation cones is basically constant. This indicates that the electron density does not significantly deviates from the r$^{-2}$ law (constant ionisation parameter). This result combined with previous optical studies suggest two plausible but different scenarios in the reconstruction of the last 30000 years history of the central AGN. The most promising one is that the source is indeed a "quasar relic" with steady and inefficient energy release from the accretion of matter onto the central super-massive black-hole. This scenario is suggested also by the flat nuclear X-ray spectrum that suggests an advection dominate accretion flow (ADAF) like emission mechanism.
R. Gilli, C. Vignali, M. Mignoli, K. Iwasawa, A. Comastri, G. Zamorani
We investigate the possibility of using the ratio between the 2-10 keV flux and the [Ne V]3426 emission line flux (X/NeV) as a diagnostic diagram to discover heavily obscured, possibly Compton-Thick Active Galactic Nuclei (AGN) up to z~1.5. First, we calibrate a relation between X/NeV and the cold absorbing column density N_H using a sample of 74 bright, nearby Seyferts with both X-ray and [Ne V] data available in the literature. Similarly to what is found for the X-ray to [O III]5007 flux ratio (X/OIII), we found that the X/NeV ratio decreases towards large column densities. Essentially all local Seyferts with X/NeV values below 15 are found to be Compton-Thick objects. Second, we apply this diagnostic diagram to different samples of distant obscured and unobscured QSOs in the SDSS: blue, unobscured, type-1 QSOs in the redshift range z=[0.1-1.5] show X/NeV values typical of unobscured Seyfert 1s in the local Universe. Conversely, SDSS type-2 QSOs at z~0.5 classified either as Compton-Thick or Compton-Thin on the basis of their X/OIII ratio, would have been mostly classified in the same way based on the X/NeV ratio. We apply the X/NeV diagnostic diagram to 9 SDSS obscured QSOs in the redshift range z=[0.85-1.31], selected by means of their prominent [Ne V]3426 line and observed with Chandra ACIS-S for 10ks each. Based on the X/NeV ratio, complemented by X-ray spectral analysis, 2 objects appear good Compton-Thick QSO candidates, 4 objects appear as Compton-Thin QSOs, while 3 have an ambiguous classification. When excluding from the sample broad lined QSOs with a red continuum and thus considering only genuine narrow-line objects, the efficiency in selecting Compton-Thick QSOs through the [Ne V] line is about 50% (with large errors, though), more similar to what is achieved with [O III] selection. [abridged]
E. Lusso, A. Comastri, C. Vignali, G. Zamorani, M. Brusa, R. Gilli, K. Iwasawa, M. Salvato, F. Civano, M. Elvis, A. Merloni, A. Bongiorno, J. R. Trump, A. M. Koekemoer, E. Schinnerer, E. Le Floc'h, N. Cappelluti, K. Jahnke, M. Sargent, J. Silverman, V. Mainieri, F. Fiore, M. Bolzonella, O. Le Fèvre, B. Garilli, A. Iovino, J. P. Kneib, F. Lamareille, S. Lilly, M. Mignoli, M. Scodeggio, D. Vergani
Dec 21, 2009·astro-ph.CO·PDF We present a study of the X-ray to optical properties of a sample of 545 X-ray selected Type 1 AGN, from the XMM-COSMOS survey, over a wide range of redshifts ($0.04<\z<4.25$) and X-ray luminosities ($40.6 \leq \Log \Lhard \leq 45.3$). About 60% of them are spectroscopically identified Type 1 AGN, while the others have a reliable photometric redshift and are classified as Type 1 AGN on the basis of their multi-band Spectral Energy Distributions. We discuss the relationship between UV and X-ray luminosity, as parameterized by the $\alphaox$ spectral slope, and its dependence on redshift and luminosity. We compare our findings with previous investigations of optically selected broad-line AGN (mostly from SDSS). A highly significant correlation between $\alphaox$ and $\lo$ is found, in agreement with previous investigations of optically selected samples. We calculate bolometric corrections, $\kbol$, for the whole sample using hard X-ray luminosities ($\Lhard$), and the Eddington ratios for a subsample of 150 objects for which black hole mass estimates are available. We confirm the trend of increasing bolometric correction with increasing Eddington ratio as proposed in previous works. A tight correlation is found between $\alphaox$ and $\kbol$, which can be used to estimate accurate bolometric corrections using only optical and X-ray data. We find a significant correlation between $\alphaox$ and Eddington ratio, in which $\alphaox$ increases for increasing Eddington ratios.
R. Gilli, J. Su, C. Norman, C. Vignali, A. Comastri, P. Tozzi, P. Rosati, M. Stiavelli, W. N. Brandt, Y. Q. Xue, B. Luo, M. Castellano, A. Fontana, F. Fiore, V. Mainieri, A. Ptak
Feb 23, 2011·astro-ph.CO·PDF We report the discovery of a Compton-thick Active Galactic Nucleus (AGN) at z=4.76 in the 4 Ms Chandra Deep Field South. This object was selected as a V-band dropout in HST/ACS images and previously recognized as an AGN from optical spectroscopy. The 4 Ms Chandra observations show a significant (~4.2sigma) X-ray detection at the V-band dropout position. The X-ray source displays a hardness ratio of HR=0.23+-0.24, which, for a source at z~5, is highly suggestive of Compton-thick absorption. The source X-ray spectrum is seen above the background level in the energy range of ~0.9-4 keV, i.e., in the rest-frame energy range of ~5-23 keV. When fixing the photon index to Gamma=1.8, the measured column density is N_H=1.4^{+0.9}_{-0.5} x 10^{24} cm^{-2}, which is Compton-thick. To our knowledge, this is the most distant heavily obscured AGN, confirmed by X-ray spectral analysis, discovered so far. The intrinsic (de-absorbed), rest-frame luminosity in the 2-10 keV band is ~2.5 x 10^{44} erg s^{-1}, which places this object among type-2 quasars. The Spectral Energy Distribution shows that massive star formation is associated with obscured black hole accretion. This system may have then been caught during a major co-eval episode of black hole and stellar mass assembly at early times. The measure of the number density of heavily obscured AGN at high redshifts will be crucial to reconstruct the BH/galaxy evolution history from the beginning.
F. Civano, M. Brusa, A. Comastri, M. Elvis, M. Salvato, G. Zamorani, P. Capak, F. Fiore, R. Gilli, H. Hao, H. Ikeda, Y. Kakazu, J. S. Kartaltepe, D. Masters, T. Miyaji, M. Mignoli, S. Puccetti, F. Shankar, J. Silverman, C. Vignali, A. Zezas, A. M. Koekemoer
Mar 14, 2011·astro-ph.CO·PDF We present the high redshift (3<z<5.3) 0.5-2 keV number counts and the 2-10 keV (rest frame) space density of X-ray selected AGNs detected in the Chandra COSMOS survey. The sample comprises 81 X-ray detected sources with available spectroscopic (31) and photometric (50) redshifts plus 20 sources with a formal z_phot<3 but with a broad photometric redshift probability distribution, such that z_phot+1sigma>3. 81 sources are selected in the 0.5-2 keV band, 14 are selected in the 2-10 keV and 6 in the 0.5-10 keV bands. We sample the high luminosity (log L_(2-10 keV)>44.15 erg/s) space density up to z~5 and a fainter luminosity range (43.5<log L(2-10 keV)<44.15 erg/s) than previous studies, up to z=3.5. We weighted the contribution to the number counts and the space density of the sources with photometric redshift by using their probability of being at z>3. We find that the space density of high-luminosity AGNs declines exponentially at all the redshifts, confirming the trend observed for optically selected quasars. At lower luminosity, the measured space density is not conclusive, and a larger sample of faint sources is needed. Comparisons with optical luminosity functions and BH formation models are presented together with prospects for future surveys.
I. Georgantopoulos, E. Rovilos, A. Comastri
Oct 18, 2010·astro-ph.CO·PDF We explore the X-ray properties of the 126 sub-mm galaxies (SMGs) of the LABOCA survey in the CDFS and the eCDFS regions. SMGs are believed to experience massive episodes of star-formation. Our goal is to examine whether star-formation coexists with AGN activity, determine the fraction of highly obscured AGN and finally to obtain an idea of the dominant power-mechanism in these sources. Using Spitzer and radio arc-second positions for the SMGs, we find 14 sources with significant X-ray detections. For most of these there are only photometric redshifts available, with their median redshift being ~2.3. Taking into account only the CDFS area which has the deepest X-ray observations, we estimate an X-ray AGN fraction of <26+/-9 % among SMGs. The X-ray spectral properties of the majority of the X-ray AGN which are associated with SMGs are consistent with high obscuration, 10^23 cm-2, but there is no unambiguous evidence for the presence of Compton-thick sources. Detailed Spectral Energy Distribution fittings show that the bulk of total IR luminosity originates in star-forming processes, although a torus component is usually present. Finally, stacking analysis of the X-ray undetected SMGs reveals a signal in the soft (0.5-2 keV) and marginally in the hard (2-5 keV) X-ray band. The hardness ratio of the stacked signal is relatively soft (-0.40+/-0.10) corresponding to a photon index of ~1.6. This argues against a high fraction of Compton-thick sources among the X-ray undetected SMGs.
G. A. Matzeu, M. Brusa, G. Lanzuisi, M. Dadina, S. Bianchi, G. Kriss, M. Mehdipour, E. Nardini, G. Chartas, R. Middei, E. Piconcelli, V. Gianolli, A. Comastri, A. L. Longinotti, Y. Krongold, F. Ricci, P. O. Petrucci, F. Tombesi, A. Luminari, L. Zappacosta, G. Miniutti, M. Gaspari, E. Behar, M. Bischetti, S. Mathur, M. Perna, M. Giustini, P. Grandi, E. Torresi, C. Vignali, G. Bruni, M. Cappi, E. Costantini, G. Cresci, B. De Marco, A. De Rosa, R. Gilli, M. Guainazzi, J. Kaastra, S. Kraemer, F. La Franca, A. Marconi, F. Panessa, G. Ponti, D. Proga, F. Ursini, F. Fiore, A. R. King, R. Maiolino, G. Matt, A. Merloni
We present a new X-ray spectroscopic study of $22$ luminous ($2\times10^{45}\lesssim L_{\rm bol}\rm /erg\,s^{-1} \lesssim 2\times10^{46}$) active galactic nuclei (AGNs) at intermediate-redshift ($0.1 \lesssim z \lesssim 0.4$), as part of the SUpermassive Black hole Winds in the x-rAYS (SUBWAYS) sample, mostly composed of quasars (QSOs) and type\,1 AGN. Here, 17 targets were observed with \textit{XMM-Newton} between 2019--2020 and the remaining 5 are from previous observations. The aim of this large campaign ($1.45\,\rm Ms$ duration) is to characterise the various manifestations of winds in the X-rays driven from supermassive black holes in AGN. In this paper we focus on the search and characterization of ultra-fast outflows (UFOs), which are typically detected through blueshifted absorption troughs in the Fe\,K band ($E>7\,\rm keV$). By following Monte Carlo procedures, we confirm the detection of absorption lines corresponding to highly ionised iron (e.g., Fe\,\textsc{xxv}\,H$α$, Fe\,\textsc{xxvi}\,Ly$α$) in 7/22 sources at the $\gtrsim95\%$ confidence level (for each individual line). The global combined probability of such absorption features in the sample is $>99.9\%$. The SUBWAYS campaign extends at higher luminosity and redshifts than previous local studies on Seyferts, obtained using \xmm and \suzaku observations. We find a UFO detection fraction of $\sim30\%$ on the total sample that is in agreement with the previous findings. This work independently provides further support for the existence of highly-ionised matter propagating at mildly relativistic speed ($\gtrsim0.1c$) in a considerable fraction of AGN over a broad range of luminosities, which is expected to play a key role in the self-regulated AGN feeding-feedback cycle, as also supported by hydrodynamical multiphase simulations.
J. D. Silverman, F. Lamareille, C. Maier, S. Lilly, V. Mainieri, M. Brusa, N. Cappelluti, G. Hasinger, G. Zamorani, M. Scodeggio, M. Bolzonella, T. Contini, C. M. Carollo, K. Jahnke, J. -P. Kneib, O. Le Fevre, A. Merloni, S. Bardelli, A. Bongiorno, H. Brunner, K. Caputi, F. Civano, A. Comastri, G. Coppa, O. Cucciati, S. de la Torre, L. de Ravel, M. Elvis, A. Finoguenov, F. Fiore, P. Franzetti, B. Garilli, R. Gilli, A. Iovino, P. Kampczyk, C. Knobel, K. Kovac, J. -F. Le Borgne, V. Le Brun, M. Mignoli, R. Pello, Y. Peng, E. Perez Montero, E. Ricciardelli, M. Tanaka, L. Tasca, L. Tresse, D. Vergani, C. Vignali, E. Zucca, D. Bottini, A. Cappi, P. Cassata, M. Fumana, R. Griffiths, J. Kartaltepe, C. Marinoni, H. J. McCracken, P. Memeo, B. Meneux, P. Oesch, C. Porciani, M. Salvato
Oct 20, 2008·astro-ph·PDF We present a study of the host galaxies of AGN selected from the zCOSMOS survey to establish if accretion onto supermassive black holes and star formation are explicitly linked up to z~1. We identify 152 galaxies that harbor AGN, based on XMM observations of 7543 galaxies (i<22.5). Star formation rates (SFRs), including those weighted by stellar mass, are determined using the [OII]3727 emission-line, corrected for an AGN contribution. We find that the majority of AGN hosts have significant levels of star formation with a distribution spanning ~1-100 Msun yr^-1. The close association between AGN activity and star formation is further substantiated by an increase in the AGN fraction with the youthfulness of their stars as indicated by the rest-frame color (U-V) and spectral index Dn(4000); we demonstrate that mass-selection alleviates an artifical peak falling in the transition region when using luminosity-limited samples. We also find that the SFRs of AGN hosts evolve with cosmic time in a manner that closely mirrors the overall galaxy population and explains the low SFRs in AGNs (z<0.3) from the SDSS. We conclude that the conditions most conducive for AGN activity are a massive host galaxy and a large reservoir of gas. Furthermore, a direct correlation between mass accretion rate onto SMBHs and SFR is shown to be weak although the average ratio is constant with redshift, effectively shifting the evidence for a co-evolution scenario in a statistical manner to smaller physical scales. Our findings illustrate an intermittent scenario with an AGN lifetime substantially shorter than that of star formation and underlying complexities regarding fueling over vastly different physical scales yet to be determined [Abridged].
C. Vignali, F. Fiore, A. Comastri, M. Brusa, R. Gilli, N. Cappelluti, F. Civano, G. Zamorani
Here we review some of the main issues related to multi-wavelength source identification and characterization, with particular emphasis on the field of X-ray surveys carried out over the last years. This complex and time-consuming process is going to represent one of the main difficulties over the coming years, when significantly larger surveys, both in area and depth, will be carried out with the new generations of space- and ground-based facilities like e.g. eROSITA, WISE, VISTA, Pan-STARRS, and LSST. The Virtual Observatory can offer a reliable way to approach to a new concept of data handling and multi-wavelength source characterization, provided that uniform and rigorous data analyses and extensive quality checks are performed.
K. Nandra, J. A. Aird, D. M. Alexander, D. R. Ballantyne, X. Barcons, F. E. Bauer, T. Boller, W. N. Brandt, M. Brusa, A. Cattaneo, G. Chartas, A. L. Coil, A. Comastri, D. J. Croton, R. Della Ceca, M. Dickinson, A. C. Fabian, G. G. Fazio, F. Fiore, K. A. Flanagan, W. R. Forman, N. Gehrels, A. Georgakakis, I. Georgantopoulos, R. Gilli, G. Hasinger, P. F. Hopkins, A. E. Hornschemeier, R. J. Ivison, G. Kauffmann, A. R. King, A. M. Koekemoer, D. C. Koo, H. Kunieda, E. S. Laird, N. A. Levenson, Y. Li, P. Madau, T. Ohashi, K. A. Pounds, J. R. Primack, P. Ranalli, G. R. Ricker, E. M. Rossi, O. Shemmer, R. S. Somerville, D. Stern, M. Stiavelli, H. Tananbaum, Y. Terashima, E. Treister, Y. Ueda, C. Vignali, M. Volonteri, M. G. Watson, N. E. White, S. D. M. White
One of the main themes in extragalactic astronomy for the next decade will be the evolution of galaxies over cosmic time. Many future observatories, including JWST, ALMA, GMT, TMT and E-ELT will intensively observe starlight over a broad redshift range, out to the dawn of the modern Universe when the first galaxies formed. It has, however, become clear that the properties and evolution of galaxies are intimately linked to the growth of their central black holes. Understanding the formation of galaxies, and their subsequent evolution, will therefore be incomplete without similarly intensive observations of the accretion light from supermassive black holes (SMBH) in galactic nuclei. To make further progress, we need to chart the formation of typical SMBH at z>6, and their subsequent growth over cosmic time, which is most effectively achieved with X-ray observations. Recent technological developments in X-ray optics and instrumentation now bring this within our grasp, enabling capabilities fully matched to those expected from flagship observatories at longer wavelengths.
P. Ranalli, A. Comastri, G. Zamorani, N. Cappelluti, F. Civano, I. Georgantopoulos, R. Gilli, E. Schinnerer, V. Smolcic, C. Vignali
Apr 19, 2012·astro-ph.CO·PDF X-ray surveys contain sizable numbers of star forming galaxies, beyond the AGN which usually make the majority of detections. Many methods to separate the two populations are used in the literature, based on X-ray and multiwavelength properties. We aim at a detailed test of the classification schemes and to study the X-ray properties of the resulting samples. We build on a sample of galaxies selected at 1.4 GHz in the VLA-COSMOS survey, classified by Smolcic et al. (2008) according to their optical colours and observed with Chandra. A similarly selected control sample of AGN is also used for comparison. We review some X-ray based classification criteria and check how they affect the sample composition. The efficiency of the classification scheme devised by Smolcic et al. (2008) is such that ~30% of composite/misclassified objects are expected because of the higher X-ray brightness of AGN with respect to galaxies. The latter fraction is actually 50% in the X-ray detected sources, while it is expected to be much lower among X-ray undetected sources. Indeed, the analysis of the stacked spectrum of undetected sources shows, consistently, strongly different properties between the AGN and galaxy samples. X-ray based selection criteria are then used to refine both samples. The radio/X-ray luminosity correlation for star forming galaxies is found to hold with the same X-ray/radio ratio valid for nearby galaxies. Some evolution of the ratio may be possible for sources at high redshift or high luminosity, tough it is likely explained by a bias arising from the radio selection. Finally, we discuss the X-ray number counts of star forming galaxies from the VLA- and C-COSMOS surveys according to different selection criteria, and compare them to the similar determination from the Chandra Deep Fields. The classification scheme proposed here may find application in future works and surveys.
D. Burlon, M. Ajello, J. Greiner, A. Comastri, A. Merloni, N. Gehrels, .
It is well accepted that unabsorbed as well as absorbed AGN are needed to explain the nature and the shape of the Cosmic X-ray background, even if the fraction of highly absorbed objects (dubbed Compton-thick sources) substantially still escapes detection. We derive and analyze the absorption distribution using a complete sample of AGN detected by Swift-BAT in the first three years of the survey. The fraction of Compton-thick AGN represents only 4.6% of the total AGN population detected by Swift-BAT. However, we show that once corrected for the bias against the detection of very absorbed sources the real intrinsic fraction of Compton-thick AGN is 20$^{+9}_{-6}$%. We proved for the first time (also in the BAT band) that the anti-correlation of the fraction of absorbed AGN and luminosity it tightly connected to the different behavior of the luminosity functions (XLFs) of absorbed and unabsorbed AGN. This points towards a difference between the two subsamples of objects with absorbed AGN being, on average, intrinsically less luminous than unobscured ones. Moreover the XLFs show that the fraction of obscured AGN might also decrease at very low luminosity. This can be successfully interpreted in the framework of a disk cloud outflow scenario as the disappearance of the obscuring region below a critical luminosity. Our results are discussed in the framework of population synthesis models and the origin of the Cosmic X-ray Background.
P. Chaudhary, M. Brusa, G. Hasinger, A. Merloni, A. Comastri, K. Nandra
Oct 17, 2011·astro-ph.CO·PDF The aim of this work is to characterize the average Fe K emission properties of active galactic nuclei (AGNs) in the source rest-frame. We selected a sample of 248 AGNs from the 2XMM catalog, covering a wide redshift range 0 < z < 5 and with the EPIC-PN net 2-10 keV rest-frame counts >=200 and power law photon indices in the range 1.5-2.2. We employed two fully independent rest-frame stacking procedures to compute the mean Fe K profile. The counting statistics for the integrated spectrum is comparable to the one available for the best studied local Seyferts. To identify the artifacts possibly introduced by the stacking procedure, we have carried out simulations. We report that the average Fe K line profile in our sample is best represented by a combination of a narrow and a broad line. The equivalent widths of the narrow and broad (parametrized with a diskline) components are ~30 eV and ~100 eV, respectively. We also discuss the results of more complex fits and the implications of the adopted continuum modeling on the broad line parameters and its detection significance.
A. Bongiorno, A. Merloni, M. Brusa, B. Magnelli, M. Salvato, M. Mignoli, G. Zamorani, F. Fiore, D. Rosario, V. Mainieri, A. Comastri, C. Vignali, I. Balestra, S. Bardelli, S. Berta, F. Civano, P. Kampczyk, E. Le Floc'h, E. Lusso, D. Lutz, L. Pozzetti, F. Pozzi, L. Riguccini, F. Shankar, J. Silverman
Using the wide multi-band photometry available in the COSMOS field we explore the host galaxy properties of a large sample of Active Galactic Nuclei (AGN) obtained by combining X-ray and optical spectroscopic selections. Based on a careful study of their Spectral Energy Distribution (SED), which has been parametrized using a 2-component (AGN+galaxy) model fit, we derived dust-corrected rest-frame magnitudes, colors, stellar masses and star formation rates (SFRs). We find that AGN hosts span a large range of stellar masses and SFRs. No color-bimodality is seen at any redshift in the AGN hosts, which are found to be mainly massive, red galaxies. Once accounting for the color-mass degeneracy in well defined mass-matched samples, we find a residual marginal enhancement of AGN incidence in redder galaxies with lower specific star formation rates, and we argue that this result might emerge because of our ability to properly account for AGN light contamination and dust extinction. Interestingly, we find that the probability for a galaxy to host a black hole growing at any given "specific accretion rate" (i.e. the ratio of X-ray luminosity to the host stellar mass) is almost independent of the host galaxy mass, while it decreases as a power-law with Lx/M. By analyzing the normalization of such probability distribution, we show how the incidence of AGN increases with redshift as rapidly as (1+z)^4, in close resemblance with the overall evolution of the specific star formation rate of the entire galaxy population. Although AGN activity and star formation in galaxies do appear to have a common triggering mechanism, at least in a statistical sense, within the COSMOS sample we do not find strong evidence of any 'smoking gun' signaling powerful AGN influence on the star-forming properties of their hosts galaxies.
N. Cappelluti, A. Kashlinsky, R. G. Arendt, A. Comastri, G. G. Fazio, A. Finoguenov, G. Hasinger, J. C. Mather, T. Miyaji, S. H. Moseley
Oct 19, 2012·astro-ph.CO·PDF In order to understand the nature of the sources producing the recently uncovered cosmic infrared background (CIB) fluctuations, we study cross-correlations between the fluctuations in the source-subtracted CIB from Spitzer/IRAC data and the unresolved cosmic X-ray background from deep Chandra observations. Our study uses data from the EGS/AEGIS field, where both data sets cover an 8'x45' region of the sky. Our measurement is the cross-power spectrum between the IR and X-ray data. The cross-power signal between the IRAC maps at 3.6 um and 4.5 um and the Chandra [0.5-2] keV data has been detected, at angular scales 20'', with an overall significance of 3.8 sigma and 5.6 sigma, respectively. At the same time we find no evidence of significant cross-correlations at the harder Chandra bands. The cross-correlation signal is produced by individual IR sources with 3.6 um and 4.5 um magnitudes m_AB 25-26 and [0.5-2] keV X-ray fluxes 7e-17 cgs.We determine that at least 15%-25% of the large scale power of the CIB fluctuations is correlated with the spatial power spectrum of the X-ray fluctuations. If this correlation is attributed to emission from accretion processes at both IR and X-ray wavelengths, this implies a much higher fraction of accreting black holes than among the known populations. We discuss the various possible origins for the cross-power signal and show that neither local foregrounds nor the known remaining normal galaxies and active galactic nuclei can reproduce the measurements. These observational results are an important new constraint on theoretical modeling of the near-IR CIB fluctuations.
G. Lanzuisi, F. Civano, M. Elvis, M. Salvato, G. Hasinger, C. Vignali, G. Zamorani, T. Aldcroft, M. Brusa, A. Comastri, F. Fiore, A. Fruscione, R. Gilli, L. C. Ho, V. Mainieri, A. Merloni, A. Siemiginowska
We present the X-ray spectral analysis of the 390 brightest extragalactic sources in the Chandra-COSMOS catalog, showing at least 70 net counts in the 0.5-7 keV band. This sample has a 100% completeness in optical-IR identification, with 75% of the sample having a spectroscopic redshift and 25% a photometric redshift. Our analysis allows us to accurately determine the intrinsic absorption, the broad band continuum shape (Γ) and intrinsic L(2-10) distributions, with an accuracy better than 30% on the spectral parameters for 95% of the sample. The sample is equally divided in type-1 (49.7%) and type-2 AGN (48.7%) plus few passive galaxies at low z. We found a significant difference in the distribution of Γ of type-1 and type-2, with small intrinsic dispersion, a weak correlation of Γ with L(2-10) and a large population (15% of the sample) of high luminosity, highly obscured (QSO2) sources. The distribution of the X ray/Optical flux ratio (Log(FX /Fi)) for type-1 is narrow (0 < X/O < 1), while type-2 are spread up to X/O = 2. The X/O correlates well with the amount of X-ray obscuration. Finally, a small sample of Compton thick candidates and peculiar sources is presented. In the appendix we discuss the comparison between Chandra and XMM-Newton spectra for 280 sources in common. We found a small systematic difference, with XMM-Newton spectra that tend to have softer power-laws and lower obscuration.
E. Merlin, A. Fontana, H. C. Ferguson, J. S. Dunlop, D. Elbaz, N. Bourne, V. A. Bruce, F. Buitrago, M. Castellano, C. Schreiber, A. Grazian, R. J. McLure, K. Okumura, X. Shu, T. Wang, R. Amorin, K. Boutsia, N. Cappelluti, A. Comastri, S. Derriere, S. M. Faber, P. Santini
May 11, 2015·astro-ph.IM·PDF We present T-PHOT, a publicly available software aimed at extracting accurate photometry from low-resolution images of deep extragalactic fields, where the blending of sources can be a serious problem for the accurate and unbiased measurement of fluxes and colours. T-PHOT has been developed within the ASTRODEEP project and it can be considered as the next generation to TFIT, providing significant improvements above it and other similar codes. T-PHOT gathers data from a high-resolution image of a region of the sky, and uses it to obtain priors for the photometric analysis of a lower resolution image of the same field. It can handle different types of datasets as input priors: i) a list of objects that will be used to obtain cutouts from the real high-resolution image; ii) a set of analytical models; iii) a list of unresolved, point-like sources, useful e.g. for far-infrared wavelength domains. We show that T-PHOT yields accurate estimations of fluxes within the intrinsic uncertainties of the method, when systematic errors are taken into account (which can be done thanks to a flagging code given in the output). T-PHOT is many times faster than similar codes like TFIT and CONVPHOT (up to hundreds, depending on the problem and the method adopted), whilst at the same time being more robust and more versatile. This makes it an optimal choice for the analysis of large datasets. In addition we show how the use of different settings and methods significantly enhances the performance. Given its versatility and robustness, T-PHOT can be considered the preferred choice for combined photometric analysis of current and forthcoming extragalactic optical to far-infrared imaging surveys. [abridged]
Michael J. Koss, C. Romero-Canizales, L. Baronchelli, S. H. Teng, M. Balokovic, S. Puccetti, F. E. Bauer, P. Arevalo, R. Assef, D. R. Ballantyne, W. N. Brandt, M. Brightman, A. Comastri, P. Gandhi, F. A. Harrison, B. Luo, K. Schawinski, D. Stern, E. Treister
May 13, 2015·astro-ph.GA·PDF We present new NuSTAR and Chandra observations of NGC 3393, a galaxy reported to host the smallest separation dual AGN resolved in the X-rays. While past results suggested a 150 pc separation dual AGN, three times deeper Chandra imaging, combined with adaptive optics and radio imaging suggest a single, heavily obscured, radio-bright AGN. Using VLA and VLBA data, we find an AGN with a two-sided jet rather than a dual AGN and that the hard X-ray, UV, optical, NIR, and radio emission are all from a single point source with a radius <0.2". We find that the previously reported dual AGN is most likely a spurious detection resulting from the low number of X-ray counts (<160) at 6-7 keV and Gaussian smoothing of the data on scales much smaller than the PSF (0.25" vs. 0.80" FWHM). We show that statistical noise in a single Chandra PSF generates spurious dual peaks of the same separation (0.55$\pm$0.07" vs. 0.6") and flux ratio (39$\pm$9% vs. 32% of counts) as the purported dual AGN. With NuSTAR, we measure a Compton-thick source (NH=$2.2\pm0.4\times10^{24}$ cm$^{-2}$) with a large torus half-opening angle, θ=79 which we postulate results from feedback from strong radio jets. This AGN shows a 2-10 keV intrinsic to observed flux ratio of 150. Using simulations, we find that even the deepest Chandra observations would severely underestimate the intrinsic luminosity of NGC 3393 above z>0.2, but would detect an unobscured AGN of this luminosity out to high redshift (z=5).
G. B. Lansbury, P. Gandhi, D. M. Alexander, R. J. Assef, J. Aird, A. Annuar, D. R. Ballantyne, M. Balokovic, F. E. Bauer, S. E. Boggs, W. N. Brandt, M. Brightman, F. E. Christensen, F. Civano, A. Comastri, W. W. Craig, A. Del Moro, B. W. Grefenstette, C. J. Hailey, F. A. Harrison, R. C. Hickox, M. Koss, S. M. LaMassa, B. Luo, S. Puccetti, D. Stern, E. Treister, C. Vignali, L. Zappacosta, W. W. Zhang
Jun 16, 2015·astro-ph.HE·PDF The intrinsic column density (NH) distribution of quasars is poorly known. At the high obscuration end of the quasar population and for redshifts z<1, the X-ray spectra can only be reliably characterized using broad-band measurements which extend to energies above 10 keV. Using the hard X-ray observatory NuSTAR, along with archival Chandra and XMM-Newton data, we study the broad-band X-ray spectra of nine optically selected (from the SDSS), candidate Compton-thick (NH > 1.5e24 cm^-2) type 2 quasars (CTQSO2s); five new NuSTAR observations are reported herein, and four have been previously published. The candidate CTQSO2s lie at z<0.5, have observed [OIII] luminosities in the range 8.4 < log (L_[OIII]/L_solar) < 9.6, and show evidence for extreme, Compton-thick absorption when indirect absorption diagnostics are considered. Amongst the nine candidate CTQSO2s, five are detected by NuSTAR in the high energy (8-24 keV) band: two are weakly detected at the ~ 3 sigma confidence level and three are strongly detected with sufficient counts for spectral modeling (>~ 90 net source counts at 8-24 keV). For these NuSTAR-detected sources direct (i.e., X-ray spectral) constraints on the intrinsic AGN properties are feasible, and we measure column densities ~2.5-1600 times higher and intrinsic (unabsorbed) X-ray luminosities ~10-70 times higher than pre-NuSTAR constraints from Chandra and XMM-Newton. Assuming the NuSTAR-detected type 2 quasars are representative of other Compton-thick candidates, we make a correction to the NH distribution for optically selected type 2 quasars as measured by Chandra and XMM-Newton for 39 objects. With this approach, we predict a Compton-thick fraction of f_CT = 36^{+14}_{-12} %, although higher fractions (up to 76%) are possible if indirect absorption diagnostics are assumed to be reliable.