THE NEXT GENERATION VIRGO CLUSTER SURVEY. XV. THE PHOTOMETRIC REDSHIFT ESTIMATION FOR BACKGROUND SOURCES

The Next Generation Virgo Cluster Survey ( NGVS) is an optical imaging survey covering 104 deg(2) centered on the Virgo cluster. Currently, the complete survey area has been observed in the u* giz bands and one third in the r band. We present the photometric redshift estimation for the NGVS background sources. After a dedicated data reduction, we perform accurate photometry, with special attention to precise color measurements through point-spread function homogenization. We then estimate the photometric redshifts with the Le Phare and BPZ codes. We add a new prior that extends to i(AB) = 12.5 mag. When using the u* griz bands, our photometric redshifts for 15.5mag <= i less than or similar to 23 mag or z(phot) less than or similar to 1 galaxies have a bias |Delta(z)| < 0.02, less than 5% outliers, a scatter sigma(outl.rej .), and an individual error on zphot that increases with magnitude ( from 0.02 to 0.05 and from 0.03 to 0.10, respectively). When using the u* giz bands over the same magnitude and redshift range, the lack of the r band increases the uncertainties in the 0.3 less than or similar to z(phot) less than or similar to 0.8 range (- 0.05 <.Delta(z)< - 0.02, sigma(outl. rej) similar to 0.06, 10%-15% outliers, and z(phot. err.) similar to 0.15). We also present a joint analysis of the photometric redshift accuracy as a function of redshift and magnitude. We assess the quality of our photometric redshifts by comparison to spectroscopic samples and by verifying that the angular auto-and cross-correlation function omega(theta) of the entire NGVS photometric redshift sample across redshift bins is in agreement with the expectations.