- What is a photometric redshift
A photometric redshift
is a measure of the galaxy distance based only on multi-color data
. Large samples of
galaxy distances can be gathered with this method allowing to study
the formation and the evolution of galaxies with huge samples of faint
We used the extremely deep multi-color
catalogues (u*g'r'i'z' filters) from the CFHT Legacy
survey produced by Terapix
T0003). A crucial point in our project was the use of a large,
deep, and representative spectroscopic sample from the VIMOS-VLT deep survey to improve
and validate out photometric redshift measurement.
We computed the photometric redshifts using
the code Le
Phare (Arnouts & Ilbert). Making use of the large VVDS
spectroscopic sample, we implemented a training method described in Ilbert, Arnouts,
McCracken et al. 2006. This training method greatly improves our
results when compared with a classic standard chi2 method. The quality
of these photo-z has been investigated in detail, as a function of
type, redshift, magnitude.
- Released catalogues
These photometric redshift
catalogues with more than 500,000 galaxies at i'ab<25 have been
released jointly by TERAPIX and the VVDS. The CENCOS database provides an
interface for a multi-criteria selection. The ascii files are
available by anonymous ftp at Terapix.
The quality of these photometric redshifts is detailed in the associated paper.