| Résumé | 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 pointspread function homogenization. We then estimate the photometric redshifts with the Le Phare and BPZ codes. We add a new prior that extends to iAB = 12.5 mag. When using the u∗griz bands, our photometric redshifts for 15.5mag ≤ i ≲ 23 mag or zphot ≲ 1 galaxies have a bias |Äz| < 0.02, less than 5% outliers, a scatter óoutl.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 ≲ zphot ≲ 0.8 range (-0.05 < Äz < -0.02, óoutl.rej ∼ 0.06, 10%-15% outliers, and zphot.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. |
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