Preliminary Study of Photometric Redshifts Based on the Wide Field Survey Telescope

The Wide Field Survey Telescope (WFST) is a dedicated time-domain multi-band (u, g, r, i, and z) photometric survey facility under construction. In this paper, we present a preliminary study that assesses the quality of photometric redshifts based on WFST by utilizing mock observations derived with the galaxy catalog in the COSMOS/UltraVISTA field. We apply the template fitting technique to estimate photometric redshifts by using the ZEBRA photometric-redshift code and adopting a modified set of adaptive templates. We evaluate the bias (median relative offset between the output photometric redshifts and input redshifts), normalized median absolute deviation (σ _NMAD) and outlier fraction (f _outlier) of photometric redshifts in two typical WFST observational cases, the single 30 s exposure observations (hereafter shallow mode) and co-added 50 minutes exposure observations (hereafter deep mode). We find bias ≲0.006, σ _NMAD ≲ 0.03, and f _outlier ≲ 5% in the shallow mode and bias ≈0.005, σ _NMAD ≈ 0.06, and f _outlier ≈ 17%-27% in the deep mode, respectively, under various lunar phases. Combining the WFST mock observational data with that from the upcoming CSST and Euclid surveys, we demonstrate that the z _phot results can be significantly improved, with f _outlier ≈ 1% and σ _NMAD ≈ 0.02.