Stacked rest-frame X-ray spectra from the 4 Ms CDF South

As part of a Chandra archive data analysis program (SP8-9001), we have extracted rest-frame X-ray spectra for all sources with robust spectroscopic redshifts in the 4 Ms Chandra Deep Field South. We have re-processed the observations, creating level 1 event files with CTI corrections but no time-dependent gain corrections (as these are applied during the spectral stacking procedure, which de-redshifts the observed energies for each photon, and creates redshift-corrected response functions which can be coadded).

Public data products

We have produced flare-cleaned event files for all CDFS pointings, using the lightcurve cleaning technique described in Hickox et al. (2006). The cleaned event files are available here (approx 350 MB).

We have also produced rest-frame spectra for sources in the Xue et al. (2011) 4 Ms CDFS catalog that have spectroscopic redshifts. This is a very large data set (4 GB); to access, please send an email to and we will send you the weblink to download the files.


In the stacked X-ray spectra, we detected significant Fe Kalpha emission for moderate-luminosity AGN (~10^42 erg/s), indicative of a large obscured population or high reflection fraction in this population. This was presented by Trouille, Hickox & Alexander in two AAS posters (figures from one example is shown below), and will be presented in an upcoming publication that also includes a modeling of the observed trend (Hickox et al. in prep).

We further explored the dependence of the average X-ray spectrum on star-formation rate, comparing the stacked spectrum for sources that are detected in Herschel far-IR observations to those that are undetected. Intriguingly, we have found that IR-detected sources have stronger Fe Kalpha lines. This work was presented in a conference poster (Chen et al., AAS HEAD meeting April 2013; example figure below) and will comprise part of his Ph.D. thesis on star formation in AGN hosts (Chen et al. in prep).

Ryan C. Hickox
Department of Physics & Astronomy
Dartmouth College
Hanover, NH 03755

Office: 241 Wilder Laboratory
Phone: +1 (603) 646-2962

Last Updated: 14 March 2017
Banner Image: courtesy of Chandra X-ray Center