Browsing by Author "Liu, Z."
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- ItemSearching for long-lived particles beyond the Standard Model at the Large Hadron Collider(2020) Alimena, J.; Beacham, J.; Borsato, M.; Cheng, Y.; Vidal, X. C.; Cottin Buracchio, Giovanna Francesca; Curtin, D.; De Roeck, A.; Desai, N.; Evans, J. A.; Knapen, S.; Kraml, S.; Lessa, A.; Liu, Z.; Mehlhase, S.; Ramsey Musolf, M. J.; Russell, H.; Shelton, J.; Shuve, B.; Verducci, M.; Zurita, J.; Adams, T.; Adersberger, M.; Alpigiani, C.; Apresyan, A.; Bainbridge, R. J.; Batozskaya, V.; Beauchesne, H.; Benato, L.; Berlendis, S.; Bhal, E.; Blekman, F.; Borovilou, C.; Boyd, J.; Brau, B. P.; Bryngemark, L.; Buchmueller, O.; Buschmann, M.; Buttinger, W.; Campanelli, M.; Cesarotti, C.; Chen, C.; Cheng, H. C.; Cheong, S.; Citron, M.; Coccaro, A.; Coco, V.; Conte, E.; Cormier, F.; Corpe, L. D.
- ItemX-ray constraints on the fraction of obscured active galactic nuclei at high accretion luminosities(OXFORD UNIV PRESS, 2017) Georgakakis, A.; Salvato, M.; Liu, Z.; Buchner, J.; Brandt, W. N.; Ananna, T. Tasnim; Schulze, A.; Shen, Yue; LaMassa, S.; Nandra, K.; Merloni, A.; McGreer, I. D.The wide-area XMM-XXL X-ray survey is used to explore the fraction of obscured active galactic nuclei (AGNs) at high accretion luminosities, L-X(2-10 keV) greater than or similar to 10(44) erg s(-1), and out to redshift z approximate to 1.5. The sample covers an area of about 14 deg(2) and provides constraints on the space density of powerful AGNs over a wide range of neutral hydrogen column densities extending beyond the Compton-thick limit, N-H approximate to 10(24) cm(-2). The fraction of obscured Compton-thin (N-H = 10(22) - 10(24) cm(-2)) AGNs is estimated to be approximate to 0.35 for luminosities L-X(2-10 keV) > 10(44) erg s(-1), independent of redshift. For less luminous sources, the fraction of obscured Compton-thin AGNs increases from 0.45 +/- 0.10 at z = 0.25 to 0.75 +/- 0.05 at z = 1.25. Studies that select AGNs in the infrared via template fits to the observed spectral energy distribution of extragalactic sources estimate space densities at high accretion luminosities consistent with the XMM-XXL constraints. There is no evidence for a large population of AGNs (e.g. heavily obscured) identified in the infrared and missed at X-ray wavelengths. We further explore the mid-infrared colours of XMM-XXL AGNs as a function of accretion luminosity, column density and redshift. The fraction of XMM-XXL sources that lie within the mid-infrared colour wedges defined in the literature to select AGNs is primarily a function of redshift. This fraction increases from about 20-30 per cent at z = 0.25 to about 50-70 per cent at z = 1.5.