Browsing by Author "Vignali, C."

Now showing 1 - 8 of 8
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    An X-ray fading, UV brightening QSO at z ≈ 6
    (2022) Vito, F.; Mignoli, M.; Gilli, R.; Brandt, W. N.; Shemmer, O.; Bauer, F. E.; Bisogni, S.; Luo, B.; Marchesi, S.; Nanni, R.; Zamorani, G.; Comastri, A.; Cusano, F.; Gallerani, S.; Vignali, C.; Lanzuisi, G.
    Explaining the existence of super massive black holes (SMBHs) with M-BH greater than or similar to 10(8) M-circle dot at z greater than or similar to 6 is a persistent challenge to modern astrophysics. Multiwavelength observations of z greater than or similar to 6 quasi-stellar objects (QSOs) reveal that, on average, their accretion physics is similar to that of their counterparts at lower redshift. However, QSOs showing properties that deviate from the general behavior can provide useful insights into the physical processes responsible for the rapid growth of SMBHs in the early universe. We present X-ray (XMM-Newton, 100 ks) follow-up observations of a z approximate to 6 QSO, J1641+3755, which was found to be remarkably X-ray bright in a 2018 Chandra dataset. J1641+3755 is not detected in the 2021 XMM-Newton observation, implying that its X-ray flux decreased by a factor greater than or similar to 7 on a notably short timescale (i.e., approximate to 115 rest-frame days), making it the z > 4 QSO with the largest variability amplitude. We also obtained rest-frame ultraviolet (UV) spectroscopic and photometric data with the Large Binocular Telescope (LBT). Surprisingly, comparing our LBT photometry with archival data, we found that J1641+3755 became consistently brighter in the rest-frame UV band from 2003 to 2016, while no strong variation occurred from 2016 to 2021. Its rest-frame UV spectrum is consistent with the average spectrum of high-redshift QSOs. Multiple narrow absorption features are present, and several of them can be associated with an intervening system at z = 5 :67. Several physical causes can explain the variability properties of J1641+3755, including intrinsic variations of the accretion rate, a small-scale obscuration event, gravitational lensing due to an intervening object, and an unrelated X-ray transient in a foreground galaxy in 2018. Accounting for all of the z > 6 QSOs with multiple X-ray observations separated by more that ten rest-frame days, we found an enhancement of strongly (i.e., by a factor >3) X-ray variable objects compared to QSOs at later cosmic times. This finding may be related to the physics of fast accretion in high-redshift QSOs.
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    Discovery of the first heavily obscured QSO candidate at z > 6 in a close galaxy pair
    (2019) Vito, F.; Brandt, W. N.; Bauer, F. E.; Gilli, R.; Luo, B.; Zamorani, G.; Calura, F.; Comastri, A.; Mazzucchelli, C.; Mignoli, M.; Nanni, R.; Shemmer, O.; Vignali, C.; Brusa, M.; Cappelluti, N.; Civano, F.; Volonteri, M.
    While theoretical arguments predict that most of the early growth of supermassive black holes (SMBHs) happened during heavily obscured phases of accretion, current methods used for selecting z > 6 quasars (QSOs) are strongly biased against obscured QSOs, thus considerably limiting our understanding of accreting SMBHs during the first gigayear of the Universe from an observational point of view. We report the Chandra discovery of the first heavily obscured QSO candidate in the early universe, hosted by a close (approximate to 5 kpc) galaxy pair at z = 6.515. One of the members is an optically classified type-1 QSO, PSO167-13. The companion galaxy was first detected as a [C II] emitter by Atacama large millimeter array (ALMA). An X-ray source is significantly (P = 0.9996) detected by Chandra in the 2-5 keV band, with < 1.14 net counts in the 0.5-2 keV band, although the current positional uncertainty does not allow a conclusive association with either PSO167-13 or its companion galaxy. From X-ray photometry and hardness-ratio arguments, we estimated an obscuring column density of N-H > 2 x 10(24) cm(-2) and N-H > 6 x 10(23) cm(-2) at 68% and 90% confidence levels, respectively. Thus, regardless of which of the two galaxies is associated with the X-ray emission, this source is the first heavily obscured QSO candidate at z > 6.
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    MOONS: The New Multi-Object Spectrograph for the VLT
    (2020) Cirasuolo, M.; Fairley, A.; Rees, P.; González, O. A.; Taylor, W.; Maiolino, R.; Afonso, J.; Evans, C.; Flores, H.; Lilly, S.; Oliva, E.; Paltani, S.; Vanzi, L.; Abreu, M.; Accardo, M.; Adams, N.; Álvarez Méndez, D.; Amans, J. -P.; Amarantidis, S.; Atek, H.; Atkinson, D.; Banerji, M.; Barrett, J.; Barrientos, F.; Bauer, F.; Beard, S.; Béchet, C.; Belfiore, A.; Bellazzini, M.; Benoist, C.; Best, P.; Biazzo, K.; Black, M.; Boettger, D.; Bonifacio, P.; Bowler, R.; Bragaglia, A.; Brierley, S.; Brinchmann, J.; Brinkmann, M.; Buat, V.; Buitrago, F.; Burgarella, D.; Burningham, B.; Buscher, D.; Cabral, A.; Caffau, E.; Cardoso, L.; Carnall, A.; Carollo, M.; Castillo, R.; Castignani, G.; Catelan, Márcio; Cicone, C.; Cimatti, A.; Cioni, M. -R. L.; Clementini, G.; Cochrane, W.; Coelho, J.; Colling, M.; Contini, T.; Contreras, R.; Conzelmann, R.; Cresci, G.; Cropper, M.; Cucciati, O.; Cullen, F.; Cumani, C.; Curti, M.; Da Silva, A.; Daddi, E.; Dalessandro, E.; Dalessio, F.; Dauvin, L.; Davidson, G.; de Laverny, P.; Delplancke-Ströbele, F.; De Lucia, G.; Del Vecchio, C.; Dessauges-Zavadsky, M.; Di Matteo, P.; Dole, H.; Drass, H.; Dunlop, J.; Dünner, R.; Eales, S.; Ellis, R.; Enriques, B.; Fasola, G.; Ferguson, A.; Ferruzzi, D.; Fisher, M.; Flores, M.; Fontana, A.; Forchi, V.; Francois, P.; Franzetti, P.; Gargiulo, A.; Garilli, B.; Gaudemard, J.; Gieles, M.; Gilmore, G.; Ginolfi, M.; Gomes, J. M.; Guinouard, I.; Gutierrez, P.; Haigron, R.; Hammer, F.; Hammersley, P.; Haniff, C.; Harrison, C.; Haywood, M.; Hill, V.; Hubin, N.; Humphrey, A.; Ibata, R.; Infante, L.; Ives, D.; Ivison, R.; Iwert, O.; Jablonka, P.; Jakob, G.; Jarvis, M.; King, D.; Kneib, J. -P.; Laporte, P.; Lawrence, A.; Lee, D.; Li Causi, G.; Lorenzoni, S.; Lucatello, S.; Luco, Y.; Macleod, A.; Magliocchetti, M.; Magrini, L.; Mainieri, V.; Maire, C.; Mannucci, F.; Martin, N.; Matute, I.; Maurogordato, S.; McGee, S.; Mcleod, D.; McLure, R.; McMahon, R.; Melse, B. -T.; Messias, H.; Mucciarelli, A.; Nisini, B.; Nix, J.; Norberg, P.; Oesch, P.; Oliveira, A.; Origlia, L.; Padilla, N.; Palsa, R.; Pancino, E.; Papaderos, P.; Pappalardo, C.; Parry, I.; Pasquini, L.; Peacock, J.; Pedichini, F.; Pello, R.; Peng, Y.; Pentericci, L.; Pfuhl, O.; Piazzesi, R.; Popovic, D.; Pozzetti, L.; Puech, M.; Puzia, T.; Raichoor, A.; Randich, S.; Recio-Blanco, A.; Reis, S.; Reix, F.; Renzini, A.; Rodrigues, M.; Rojas, Felipe; Rojas-Arriagada, Á.; Rota, S.; Royer, F.; Sacco, G.; Sanchez-Janssen, R.; Sanna, N.; Santos, P.; Sarzi, M.; Schaerer, D.; Schiavon, R.; Schnell, R.; Schultheis, M.; Scodeggio, M.; Serjeant, S.; Shen, T. -C.; Simmonds, C.; Smoker, J.; Sobral, D.; Sordet, M.; Spérone, D.; Strachan, J.; Sun, X.; Swinbank, M.; Tait, G.; Tereno, I.; Tojeiro, R.; Torres, M.; Tosi, M.; Tozzi, A.; Tresiter, E.; Valenti, E.; Valenzuela Navarro, Á.; Vanzella, E.; Vergani, S.; Verhamme, A.; Vernet, J.; Vignali, C.; Vinther, J.; Von Dran, L.; Waring, C.; Watson, S.; Wild, V.; Willesme, B.; Woodward, B.; Wuyts, S.; Yang, Y.; Zamorani, G.; Zoccali, M.; Bluck, A.; Trussler, J.
    MOONS is the new Multi-Object Optical and Near-infrared Spectrograph currently under construction for the Very Large Telescope (VLT) at ESO. This remarkable instrument combines, for the first time, the collecting power of an 8-m telescope, 1000 fibres with individual robotic positioners, and both low- and high-resolution simultaneous spectral coverage across the 0.64-1.8 μm wavelength range. This facility will provide the astronomical community with a powerful, world-leading instrument able to serve a wide range of Galactic, extragalactic and cosmological studies. Construction is now proceeding full steam ahead and this overview article presents some of the science goals and the technical description of the MOONS instrument. More detailed information on the MOONS surveys is provided in the other dedicated articles in this Messenger issue....
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    NuSTAR. reveals the extreme properties of the super-Eddington accreting supermassive black hole in PG. 1247+267
    (2016) Lanzuisi, G.; Perna, M.; Comastri, A.; Cappi, M.; Dadina, M.; Marinucci, A.; Masini, A.; Matt, G.; Vagnetti, F.; Bauer, Franz Erik; Vignali, C.; Ballantyne, D.; Boggs, S.; Brandt, W.; Brusa, M.; Craig, W.; Ricci, Claudio
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    THE 4 Ms CHANDRA DEEP FIELD-SOUTH NUMBER COUNTS APPORTIONED BY SOURCE CLASS: PERVASIVE ACTIVE GALACTIC NUCLEI AND THE ASCENT OF NORMAL GALAXIES
    (2012) Lehmer, B. D.; Xue, Y. Q.; Brandt, W. N.; Alexander, D. M.; Bauer, F. E.; Brusa, M.; Comastri, A.; Gilli, R.; Hornschemeier, A. E.; Luo, B.; Paolillo, M.; Ptak, A.; Shemmer, O.; Schneider, D. P.; Tozzi, P.; Vignali, C.
    We present 0.5-2 keV, 2-8 keV, 4-8 keV, and 0.5-8 keV (hereafter soft, hard, ultra-hard, and full bands, respectively) cumulative and differential number-count (log N-log S) measurements for the recently completed approximate to 4 Ms Chandra Deep Field-South (CDF-S) survey, the deepest X-ray survey to date. We implement a new Bayesian approach, which allows reliable calculation of number counts down to flux limits that are factors of approximate to 1.9-4.3 times fainter than the previously deepest number-count investigations. In the soft band (SB), the most sensitive bandpass in our analysis, the approximate to 4 Ms CDF-S reaches a maximum source density of approximate to 27,800 deg(-2). By virtue of the exquisite X-ray and multiwavelength data available in the CDF-S, we are able to measure the number counts from a variety of source populations (active galactic nuclei (AGNs), normal galaxies, and Galactic stars) and subpopulations (as a function of redshift, AGN absorption, luminosity, and galaxy morphology) and test models that describe their evolution. We find that AGNs still dominate the X-ray number counts down to the faintest flux levels for all bands and reach a limiting SB source density of approximate to 14,900 deg(-2), the highest reliable AGN source density measured at any wavelength. We find that the normal-galaxy counts rise rapidly near the flux limits and, at the limiting SB flux, reach source densities of approximate to 12,700 deg(-2) and make up 46% +/- 5% of the total number counts. The rapid rise of the galaxy counts toward faint fluxes, as well as significant normal-galaxy contributions to the overall number counts, indicates that normal galaxies will overtake AGNs just below the approximate to 4 Ms SB flux limit and will provide a numerically significant new X-ray source population in future surveys that reach below the approximate to 4 Ms sensitivity limit. We show that a future approximate to 10 Ms CDF-S would allow for a significant increase in X-ray-detected sources, with many of the new sources being cosmologically distant (z greater than or similar to 0.6) normal galaxies.
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    The X-ray properties of z > 6 quasars: no evident evolution of accretion physics in the first Gyr of the Universe
    (2019) Vito, F.; Brandt, W. N.; Bauer, F. E.; Calura, F.; Gilli, R.; Luo, B.; Shemmer, O.; Vignali, C.; Zamorani, G.; Brusa, M.; Civano, F.; Comastri, A.; Nanni, R.
    Context. X-ray emission from quasars (QSOs) has been used to assess supermassive black hole accretion properties up to z approximate to 6. However, at z > 6 only approximate to 15 QSOs are covered by sensitive X-ray observations, preventing a statistically significant investigation of the X-ray properties of the QSO population in the first Gyr of the Universe.
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    Universal bolometric corrections for active galactic nuclei over seven luminosity decades
    (2020) Duras, F.; Bongiorno, A.; Ricci, F.; Piconcelli, E.; Shankar, F.; Lusso, E.; Bianchi, S.; Fiore, F.; Maiolino, R.; Marconi, A.; Onori, F.; Sani, E.; Schneider, R.; Vignali, C.; La Franca, F.
    Context. The AGN bolometric correction is a key element for understanding black hole (BH) demographics and computing accurate BH accretion histories from AGN luminosities. However, current estimates still differ from each other by up to a factor of two to three, and rely on extrapolations at the lowest and highest luminosities.
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    X-ray emission of z > 2.5 active galactic nuclei can be obscured by their host galaxies
    (2019) Circosta, C.; Vignali, C.; Gilli, R.; Feltre, A.; Vito, F.; Calura, F.; Mainieri, V; Massardi, M.; Norman, C.
    We present a multiwavelength study of seven active galactic nuclei (AGN) at spectroscopic redshift >2.5 in the 7 Ms Chandra Deep Field South that were selected for their good far-infrared (FIR) and submillimeter (submm) detections. Our aim is to investigate the possibility that the obscuration observed in the X-rays can be produced by the interstellar medium (ISM) of the host galaxy. Based on the 7 Ms Chandra spectra, we measured obscuring column densities N-H,N- X in excess of 7 x 10(22) cm(-2) and intrinsic X-ray luminosities L-X > 10(44) erg s(-1) for our targets, as well as equivalent widths for the Fe K alpha emission line EWrest greater than or similar to 0.5-1 keV. We built the UV-to-FIR spectral energy distributions (SEDs) by using broadband photometry from the CANDELS and Herschel catalogs. By means of an SED decomposition technique, we derived stellar masses (M-* similar to 10(11) M-circle dot), IR luminosities (L-IR > 10(12) L-circle dot), star formation rates (SFR similar to 190-1680 M-circle dot yr(-1)) and AGN bolometric luminosities (L-bol similar to 10(46) erg s(-1)) for our sample. We used an empirically calibrated relation between gas masses and FIR/submm luminosities and derived M-gas similar to 0.8-5.4 x 10(10) M-circle dot. High-resolution (0.3-0.7 '') ALMA data (when available, CANDELS data otherwise) were used to estimate the galaxy size and hence the volume enclosing most of the ISM under simple geometrical assumptions. These measurements were then combined to derive the column density associated with the ISM of the host, which is on the order of N-H,N- ISM similar to 10(23-24) cm(-2). The comparison between the ISM column densities and those measured from the X-ray spectral analysis shows that they are similar. This suggests that at least at high redshift, significant absorption on kiloparsec scales by the dense ISM in the host likely adds to or substitutes that produced by circumnuclear gas on parsec scales (i.e., the torus of unified models). The lack of unobscured AGN among our ISM-rich targets supports this scenario.