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 deg² 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 15.5 mag <= i <~ 23 mag or z _phot <~ 1 galaxies have a bias |Δz| < 0.02, less than 5% outliers, a scatter σ_outl.rej., and an individual error on z _phot 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 <~ z _phot <~ 0.8 range (-0.05 < Δz < -0.02, σ_outl.rej ~ 0.06, 10%-15% outliers, and z _phot.err. ~ 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 w(θ) of the entire NGVS photometric redshift sample across redshift bins is in agreement with the expectations.