A Detailed Study of Photometric Redshifts for GOODS-South Galaxies
  We use the deepest and the most comprehensive photometric data currently
available for GOODS-South galaxies to measure their photometric redshifts. The
photometry includes VLT/VIMOS (U-band), HST/ACS (F435W, F606W, F775W, and
F850LP bands), VLT/ISAAC (J-, H-, and Ks-bands), and four Spitzer/IRAC channels
(3.6, 4.5, 5.8, and 8.0 micron). The catalog is selected in the z-band (F850LP)
and photometry in each band is carried out using the recently completed TFIT
algorithm, which performs PSF matched photometry uniformly across different
instruments and filters, despite large variations in PSFs and pixel scales.
Photometric redshifts are derived using the GOODZ code, which is based on the
template fitting method using priors. The code also implements "training" of
the template SED set, using available spectroscopic redshifts in order to
minimize systematic differences between the templates and the SEDs of the
observed galaxies. Our final catalog covers an area of 153 sq. arcmin and
includes photometric redshifts for a total of 32,505 objects. The scatter
between our estimated photometric and spectroscopic redshifts is sigma=0.040
with 3.7% outliers to the full z-band depth of our catalog, decreasing to
sigma=0.039 and 2.1% outliers at a magnitude limit m(z)<24.5. This is
consistent with the best results previously published for GOODS-S galaxies,
however, the present catalog is the deepest yet available and provides
photometric redshifts for significantly more objects to deeper flux limits and
higher redshifts than earlier works. Furthermore, we show that the photometric
redshifts estimated here for galaxies selected as dropouts are consistent with
those expected based on the Lyman break technique.
