Forecasts on CMB lensing observations with AliCPT-1

Abstract

AliCPT-1 is the first Chinese cosmic microwave background (CMB) experiment aiming for the high-precision measurement of CMB B-mode polarization. The telescope, currently under deployment in Tibet, will observe in two frequency bands centered at 90 and 150 GHz. We forecast the CMB lensing reconstruction, lensing-galaxy, and lensing-cosmic infrared background (CIB) cross-correlation signal-to-noise ratio (SNR) for AliCPT-1. We consider two stages with different integrated observation times, namely “4 module*yr” (first stage) and “48 module*yr” (final stage). For lensing reconstruction, we use three different quadratic estimators, namely temperature-only, polarization-only and minimum-variance (MV) estimators, using curved sky geometry. We take into account the impacts of inhomogeneous hit counts and mean-field bias due to incomplete sky coverage. In the first stage, our results show that the 150 GHz channel can measure the lensing signals at 15cr significance with the MV estimator. In the final stage, the measurement significance will increase to 31σ. We also combine the two frequency data in the harmonic domain to optimize the SNR. Our results show that the coadding procedure can significantly reduce the reconstruction bias in the high multiple range. Owning to the high quality of the polarization data in the final stage of AliCPT-1, the EB estimator will dominate the lensing reconstruction in this stage. We also estimate the SNR of cross-correlations between AliCPT-1 CMB lensing and other tracers of the large scale structure of the universe. For its cross-correlation with Dark Energy Spectroscopic Instrument (DESI) galaxies/quasars, we report the cross-correlation SNR = 10–20 for the four redshift bins at 0.05 < z < 2.1. In the first stage, the total SNR is approximately 32. In the final stage, the lensing-galaxy cross-correlation can reach SNR = 52. For lensing-CTB cross-correlation, in the first stage, the cross-correlations between AliCPT-1 lensing and Planck CIB 353, 545 and 857 GHz channels are approximately SNR =18,19, and 23, respectively. In the final stage, the cross-correlations can reach SNR = 25,33 and 42. Due to the strong correlations between frequency bands, the total lensing-CIB cross-correlations by combining the three frequencies in Planck CIBs are SNR = 23 and 43 for the AliCPT-1 first and final stages, respectively.