A Cross-internal Linear Combination Approach to Probe the Secondary CMB Anisotropies: Kinematic Sunyaev–Zel’dovich Effect and CMB Lensing

Abstract We propose a cross-internal linear combination (cross-ILC) approach to measure the small-scale cosmic microwave background (CMB) anisotropies robustly against contamination from astrophysical signals. In particular, we focus on mitigation of systematics infrared (CIB) and thermal Sunyaev–Zel’dovich (tSZ) signals in kinematic (kSZ) power spectrum CMB lensing. show cross-spectrum measurement between two maps created by nulling contributions CIB (CIB-free map) tSZ (tSZ-free be robust for kSZ, as significantly suppresses total contribution Similarly, lensing, use introduced Madhavacheril & Hill but with slight modification using tSZ-free CIB-free legs quadratic estimator. By cross-correlating lensing map this technique galaxy surveys, that biases both are negligible. also compute impact unmodeled CIB/tSZ residuals kSZ cosmological parameters, finding measured standard ILC biased. The estimate cross-ILC remains less affected CIB/tSZ, making it crucial current upcoming surveys such South Pole Telescope (SPT), Simons Observatory (SO), CMB-S4. With approach, find can at very high significance coming years: 35 σ SPT, 22 SO, 80 Finally, forecast constraints epoch reionization duration reionization, currently unconstrained Planck, constrained σ ( Δ z re stretchy="false">) = 1.5 or 0.5 depending choice prior optical depth reionization. data products associated codes downloaded link ( https://github.com/sriniraghunathan/cross_ilc_methods_paper ).