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arXiv · 1111.2447

Fe K emission from active galaxies in the COSMOS field

K. Iwasawa·V. Mainieri·M. Brusa·A. Comastri·R. Gilli·C. Vignali·G. Hasinger·D. B. Sanders·N. Cappelluti·C. D. Impey·A. Koekemoer·G. Lanzuisi·E. Lusso·A. Merloni·M. Salvato·Y. Taniguchi·J. R. Trump
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Abstract

We present a rest-frame spectral stacking analysis of ~1000 X-ray sources detected in the XMM-COSMOS field in order 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~1.5e44 erg/s and z~1.6, the cold Fe K at 6.4 keV is weak (EW~0.05keV), in agreement 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, when the X-ray luminosity is restricted to the range below 3e44 erg/s, or when an intermediate range of Eddington ratio around 0.1 is selected. In Type II AGN, both cold and high-ionzation lines become weak with increasing X-ray luminosity. However, strong high-ionization Fe K (EW~0.3 keV) is detected in the spectrum of objects at z>2, while no 6.4 keV line is found. It is then found that the primary source of the high-ionization Fe K emission is those objects detected with Spitzer-MIPS at 24 micron. Given their median redshift of z=2.5, their bolometric luminosity is likely to reach 10^13 Lsun 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.

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K. Iwasawa, V. Mainieri, M. Brusa, A. Comastri, R. Gilli, C. Vignali, G. Hasinger, D. B. Sanders, N. Cappelluti, C. D. Impey, A. Koekemoer, G. Lanzuisi, E. Lusso, A. Merloni, M. Salvato, Y. Taniguchi, J. R. Trump. 2011-11-10. Fe K emission from active galaxies in the COSMOS field. https://doi.org/10.1051/0004-6361%2F201118203

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