. . . . . . . . . . . "We present a rest-frame spectral stacking analysis of \u00A0~1000 X-ray sources detected in the XMM-COSMOS field to investigate the iron-K line properties of active galaxies beyond redshift z\u00A0~\u00A01. In Type\u00A0I AGN that have a typical X-ray luminosity of LX\u00A0~\u00A01.5\u00A0\u00D7\u00A010 44\u00A0(erg s -1) and z\u00A0~\u00A01.6 the cold Fe\u00A0K at 6.4\u00A0keV is weak ( EW\u00A0~\u00A00.05\u00A0keV), which agrees with the known trend. In contrast, high-ionization lines of Fe xxv and Fe xxvi are pronounced. These high-ionization Fe\u00A0K 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 (~2 \u03C3), when the X-ray luminosity is restricted to the range below 3\u00A0\u00D7\u00A010 44\u00A0erg s -1, or when an intermediate range of Eddington ratio around \u03BB\u00A0~\u00A00.1 is selected. In Type\u00A0II AGN, both cold and high-ionzation lines become weak with increasing X-ray luminosity. However, we detected strong high-ionization Fe\u00A0K ( EW\u00A0~\u00A00.3\u00A0keV) in the spectrum of objects at z\u00A0>\u00A02, while we found no 6.4\u00A0keV line. We also found that the primary source of the high-ionization Fe\u00A0K emission are those objects detected with Spitzer-MIPS at 24\u00A0 \u03BCm. Given their median redshift of z\u00A0\u2243\u00A02.5, their bolometric luminosity is likely to reach 10 13\u00A0\u00A0\u00A0 L\u2299 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\u00A0~\u00A02-3) of galaxy formation."@en . "aa18203-11" . . . "2012"^^ . . "2012"^^ . . . . . . . . . . . . "Fe\u00A0K emission from active galaxies in the COSMOS field"@en . . . . . . "\u00A9 ESO, 2012" . . . . . . . . . . . "ESO" . . . . . .