Chandra counterparts of CANDELS GOODS-S sources
  Improving the capabilities of detecting faint X-ray sources is fundamental to
increase the statistics on faint high-z AGN and star-forming galaxies. We
performed a simultaneous Maximum Likelihood PSF fit in the [0.5-2] keV and
[2-7] keV energy bands of the 4 Ms{\em Chandra} Deep Field South (CDFS) data at
the position of the 34930 CANDELS H-band selected galaxies. For each detected
source we provide X-ray photometry and optical counterpart validation. We
validated this technique by means of a raytracing simulation. We detected a
total of 698 X-ray point-sources with a likelihood $\mathcal{L}$$>$4.98 (i.e.
$>$2.7$\sigma$). We show that the prior knowledge of a deep sample of
Optical-NIR galaxies leads to a significant increase of the detection of faint
(i.e. $\sim$10$^{-17}$ cgs in the [0.5-2] keV band) sources with respect to
"blind" X-ray detections. By including previous X-ray catalogs, this work
increases the total number of X-ray sources detected in the 4 Ms CDFS, CANDELS
area to 793, which represents the largest sample of extremely faint X-ray
sources assembled to date. Our results suggest that a large fraction of the
optical counterparts of our X-ray sources determined by likelihood ratio
actually coincides with the priors used for the source detection. Most of the
new detected sources are likely star-forming galaxies or faint absorbed AGN. We
identified a few sources sources with putative photometric redshift z$>$4.
Despite the low number statistics and the uncertainties on the photo-z, this
sample significantly increases the number of X--ray selected candidate high-z
AGN.
