Precise self-calibration of interloper bias in spectroscopic surveys

Abstract

ABSTRACT Interloper contamination due to line misidentification is an important issue in the future low-resolution spectroscopic surveys. We realize that the algorithm previously used for photometric redshift self-calibration, with minor modifications, can be particularly applicable to calibrate the interloper bias. In order to explore the robustness of the modified self-calibration algorithm, we construct the mock catalogues based on China Space Station Telescope (CSST), taking two main target emission lines, Hα and [O iii]. The self-calibration algorithm is tested in cases with different interloper fractions at 1 per cent, 5 per cent, and 10 per cent. We find that the interloper fraction and mean redshift in each redshift bin can be successfully reconstructed at the level of ∼ 0.002 and ∼ 0.001(1 + z), respectively. We also find the impact of the cosmic magnification can be significant, which is usually ignored in previous works, and therefore propose a convenient and efficient method to eliminate it. Using the elimination method, we show that the calibration accuracy can be effectively recovered with slightly larger uncertainty.