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The X-ray spectra of Active Galactic Nuclei (AGN) carry the signatures of theemission from the central region, close to the Super Massive Black Hole (SMBH).For this reason, the study of deep X-ray spectra is a powerful instrument toinvestigate the origin of their emission.  The emission line most often observed in the X-ray spectra of AGN is Fe K. Itis known that it can be broadened and deformed by relativistic effects ifemitted close enough to the central SMBH. In recent statistical studies of theX-ray spectra of AGN samples, it is found that a narrow Fe line is ubiquitous,while whether the broad features are as common is still uncertain. We presenthere the results of an investigation on the characteristics of the Fe line inthe average X-ray spectra of AGN in deep Chandra fields.  The average spectrum of the AGN is computed using Chandra spectra with morethan 200 net counts from the AEGIS, Chandra Deep Field North and Chandra DeepField South surveys. The sample spans a broader range of X-ray luminositiesthan other samples studied with stacking methods up to z=3.5. We analyze theaverage spectra of this sample using our own averaging method, checking theresults against extensive simulations. Subsamples defined in terms of columndensity of the local absorber, luminosity and z are also investigated.  We found a very significant Fe line with a narrow profile in all our samplesand in almost all the subsamples that we constructed. The equivalent width (EW)of the narrow line estimated in the average spectrum of the full sample is 74eV. The broad line component is significantly detected in the subsample of AGNwith L<1.43 1E44 cgs and z<0.76, with EW=108 eV.  We concluded that the narrow Fe line is an ubiquitous feature of the X-rayspectra of the AGN up to z=3.5.The broad line component is significant in theX-ray spectra of the AGN with low luminosity and low z.

Averaging the AGN X-ray spectra from deep Chandra fields