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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents



ID: 660897.0, MPI für Astronomie / Publikationen_mpia
Fe K emission from active galaxies in the COSMOS field
Authors:Iwasawa, K.; Mainieri, V.; Brusa, M.; Comastri, A.; Gilli, R.; Vignali, C.; Hasinger, G.; Sanders, D. B.; Cappelluti, N.; Impey, C. D.; Koekemoer, A.; Lanzuisi, G.; Lusso, E.; Merloni, A.; Salvato, M.; Taniguchi, Y.; Trump, J. R.
Date of Publication (YYYY-MM-DD):2012
Journal Abbrev.:Astronomy and Astrophysics
Volume:537
Start Page:id.A86
Audience:Not Specified
Abstract / Description:We present a rest-frame spectral stacking analysis of ~1000 X-ray sources detected in the XMM-COSMOS field to investigate the iron-K line properties of active galaxies beyond redshift z ~ 1. In Type I AGN that have a typical X-ray luminosity of LX ~ 1.5 × 1044 (erg s-1) and z ~ 1.6 the cold Fe K at 6.4 keV is weak (EW ~ 0.05 keV), which agrees with the known trend. In contrast, high-ionization lines of Fe xxv and Fe xxvi are pronounced. These high-ionization Fe K lines appear to have a connection with high accretion rates. While no broad Fe emission is detected in the total spectrum, it might be present, albeit at low significance (~2σ), when the X-ray luminosity is restricted to the range below 3 × 1044 erg s-1, or when an intermediate range of Eddington ratio around λ ~ 0.1 is selected. In Type II AGN, both cold and high-ionzation lines become weak with increasing X-ray luminosity. However, we detected strong high-ionization Fe K (EW ~ 0.3 keV) in the spectrum of objects at z > 2, while we found no 6.4 keV line. We also found that the primary source of the high-ionization Fe K emission are those objects detected with Spitzer-MIPS at 24 μm. Given their median redshift of z ≃ 2.5, their bolometric luminosity is likely to reach 1013 L&sun; and the MIPS-detected emission most likely originates from hot dust heated by embedded AGN, probably accreting at high Eddington ratio. These properties match those of rapidly growing black holes in ultra-luminous infrared galaxies at the interesting epoch (z ~ 2-3) of galaxy formation.
Free Keywords:X-rays: galaxies; galaxies: active; surveys
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
Identifiers:URL:http://cdsads.u-strasbg.fr/abs/2012A%26A...537A..8...
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