Browsing by Author "Allevato, Viola"

Now showing 1 - 6 of 6
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    Black hole scaling relations of active and quiescent galaxies: Addressing selection effects and constraining virial factors
    (2019) Shankar, Francesco; Bernardi, Mariangela; Richardson, Kayleigh; Marsden, Christopher; Sheth, Ravi K.; Allevato, Viola; Graziani, Luca; Mezcua, Mar; Ricci, Federica; Penny, Samantha J.; La Franca, Fabio; Pacucci, Fabio
    Local samples of quiescent galaxies with dynamically measured black hole masses (M-bh) may suffer from an angular resolution-related selection effect, which could bias the observed scaling relations between M-bh and host galaxy properties away from the intrinsic relations. In particular, previous work has shown that the observed M-bh-M-star relation is more strongly biased than the M-bh-sigma relation. Local samples of active galactic nuclei (AGN) do not suffer from this selection effect, as in these samples M-bh is estimated from megamasers and/or reverberation mapping-based techniques. With the exception of megamasers, M-bh estimates in these AGN samples are proportional to a virial coefficient f(vir). Direct modelling of the broad-line region suggests that f(vir) similar to 3.5. However, this results in an M-bh-M-star relation for AGN, which lies below and is steeper than the one observed for quiescent black hole samples. A similar though milder trend is seen for the M-bh-sigma relation. Matching the high-mass end of the M-bh-M-star and M-bh-sigma relations observed in quiescent samples requires f(vir) greater than or similar to 15 and f(vir) greater than or similar to 7, respectively. On the other hand, f(vir) similar to 3.5 yields M-bh-sigma and M-bh-M-star relations for AGN, which are remarkably consistent with the expected 'intrinsic' correlations for quiescent samples (i.e. once account has been made of the angular resolution-related selection effect), providing additional evidence that the sample of local quiescent black holes is biased. We also show that, as is the case for quiescent black holes, the M-bh-M-star scaling relation of AGN is driven by sigma, thus providing additional key constraints to black hole-galaxy co-evolution models.
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    Constraining black hole-galaxy scaling relations and radiative efficiency from galaxy clustering
    (2020) Shankar, Francesco; Allevato, Viola; Bernardi, Mariangela; Marsden, Christopher; Lapi, Andrea; Menci, Nicola; Grylls, Philip J.; Krumpe, Mirko; Zanisi, Lorenzo; Ricci, Federica; La Franca, Fabio; Baldi, Ranieri D.; Moreno, Jorge; Sheth, Ravi K.
    The masses of supermassive black holes are observed to increase with either the total mass or the mean (random) velocity of the stars in their host galaxies. The origin of these correlations remains elusive due to observational systematics and biases that severely limit our knowledge of the local demography of supermassive black holes. Here, we show that the large-scale spatial distribution of local active galactic nuclei (AGN) can constrain the shape and normalization of the black hole-stellar mass relation, thus bypassing resolution-related observational biases. In turn, our results can set more stringent constraints on the AGN radiative efficiency, epsilon. For currently accepted values of the AGN obscured fractions and bolometric corrections, our estimated local supermassive black hole mass density favours mean epsilon values of similar to 10-20%, suggesting that the vast majority of supermassive black holes are spinning moderately to rapidly. With large-scale AGN surveys coming online, our methodology will enable even tighter constraints on the fundamental parameters that regulate the growth of supermassive black holes.
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    Probing black hole accretion tracks, scaling relations, and radiative efficiencies from stacked X-ray active galactic nuclei
    (2020) Shankar, Francesco; Weinberg, David H.; Marsden, Christopher; Grylls, Philip J.; Bernardi, Mariangela; Yang, Guang; Moster, Benjamin; Fu, Hao; Carraro, Rosamaria; Alexander, David M.; Allevato, Viola; Ananna, Tonima T.; Bongiorno, Angela; Calderone, Giorgio; Civano, Francesca; Daddi, Emanuele; Delvecchio, Ivan; Duras, Federica; La Franca, Fabio; Lapi, Andrea; Lu, Youjun; Menci, Nicola; Mezcua, Mar; Ricci, Federica; Rodighiero, Giulia; Sheth, Ravi K.; Suh, Hyewon; Villforth, Carolin; Zanisi, Lorenzo
    The masses of supermassive black holes at the centres of local galaxies appear to be tightly correlated with the mass and velocity dispersions of their galactic hosts. However, the local M-bh-M-star relation inferred from dynamically measured inactive black holes is up to an order-of-magnitude higher than some estimates from active black holes, and recent work suggests that this discrepancy arises from selection bias on the sample of dynamical black hole mass measurements. In this work, we combine X-ray measurements of the mean black hole accretion luminosity as a function of stellar mass and redshift with empirical models of galaxy stellar mass growth, integrating over time to predict the evolving M-bh-M-star relation. The implied relation is nearly independent of redshift, indicating that stellar and black hole masses grow, on average, at similar rates. Matching the de-biased local M-bh-M-star relation requires a mean radiative efficiency epsilon greater than or similar to 0.15, in line with theoretical expectations for accretion on to spinning black holes. However, matching the 'raw' observed relation for inactive black holes requires epsilon similar to 0.02, far below theoretical expectations. This result provides independent evidence for selection bias in dynamically estimated black hole masses, a conclusion that is robust to uncertainties in bolometric corrections, obscured active black hole fractions, and kinetic accretion efficiency. For our fiducial assumptions, they favour moderate-to-rapid spins of typical supermassive black holes, to achieve epsilon similar to 0.12-0.20. Our approach has similarities to the classic Soltan analysis, but by using galaxy-based data instead of integrated quantities we are able to focus on regimes where observational uncertainties are minimized.
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    The Chandra COSMOS Legacy Survey: Energy Spectrum of the Cosmic X-Ray Background and Constraints on Undetected Populations
    (2017) Cappelluti, N.; Treister, Ezequiel; Li, Yanxia; Ricarte, Angelo; Agarwal, Bhaskar; Allevato, Viola; Ananna, Tonima; Ajello, Marco; Civano, Francesca; Comastri, A.; Elvis, Martin
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    The Chandra COSMOS-Legacy Survey: Source X-Ray Spectral Properties
    (2016) Marchesi, Stefano; Treister, Ezequiel; Lanzuisi, G.; Civano, Francesca; Iwasawa, K.; Suh, H.; Comastri, A.; Zamorani, G.; Allevato, Viola; Griffiths, R.; Miyaji, T.
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    The Chandra COSMOS-Legacy Survey: The z>3 Sample
    (2016) Marchesi, Stefano; Treister, Ezequiel; Civano, Francesca; Salvato, M.; Shankar, F.; Comastri, A.; Elvis, Martin; Lanzuisi, G.; Trakhtenbrot, Benny; Vignali, C.; Zamorani, G.; Allevato, Viola