- 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
galaxies.
- Data
We used the extremely deep multi-color
catalogues (u*g'r'i'z' filters) from the CFHT Legacy
survey produced by Terapix
(released
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.
- Method
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.