Photometric Redshift Forecast for the 7-Dimensional Sky Survey

Abstract We investigate the expected accuracy of redshifts that can be obtained using low-resolution spectroscopic (medium-band) data from the 7-Dimensional Sky Survey (7DS). By leveraging 40 densely sampled filters with widths of FWHM = 25 nm, we create 7DS mock catalogs and estimate the redshift accuracy for three 7DS main surveys: the Wide-field Time-Domain Survey (WTS), the Intensive Monitoring Survey, and the Reference Imaging Survey. Using photometric redshifts calculated from EAZY , we find that the 5 yr WTS provides reliable photometric redshifts with a normalized median absolute deviation ( σ NMAD ) ranging from 0.003 to 0.007 and a catastrophic failure fraction ( η ) from 0.8% to 8.1% at 19 ≤ m 625 < 22. The spectral resolution R ∼ 50 of the medium-band data set effectively captures the 4000 Å break and various emission lines. We also explore the synergy with data obtained from the Pan-STARRS1, VIKING, and SPHEREx surveys. Combining the SPHEREx all-sky data with WTS significantly improves the accuracy of photometric redshift estimates, achieving η = 0.4% and σ NMAD = 0.004 for fainter sources at higher redshifts. The additional near-IR information provided by SPHEREx and VIKING plays an essential role in resolving degeneracies between low and high redshifts. We also observe color excesses by subtracting adjacent broadband data, which improves the confinement of photometric redshifts and aids in the detection of strong emission line galaxies.