Cross-Frequency Temperature Coherence of ACT DR6 Maps: Pair-Specific Diagnostics and Scale-Cut Recommendations for Multi-Frequency Analyses

Abstract: We present a systematic analysis of temperature cross-frequency coherence across all six Atacama Cosmology Telescope (ACT) Data Release 6 (DR6) channels at 90, 150, and 220 GHz, using the cross-correlation coefficient measured from noise-bias-free split-cross spectra on a common sky mask. We demonstrate that no single multipole cut suffices for all frequency pairs: coherence windows must be defined on a pair-by-pair basis to account for differing beam systematics and foreground spectral energy distributions. The three 150 GHz detector arrays (pa4_f150, pa5_f150, pa6_f150) exhibit the tightest internal consistency, with beam-deconvolved spectral ratios agreeing at the 10% level over a broad multipole range. Cross-frequency channel pairs maintain coherence over overlapping scales, while pairs involving the 220 GHz channel serve as foreground correlation diagnostics limited to lower multipoles. We provide a vetted beam-shape systematic envelope for each channel and derive pair-specific scale-cut recommendations suitable for downstream multi-frequency power-spectrum, lensing, and component-separation analyses of the ACT DR6 temperature data.

Subjects:	astro-ph.CO; physics.data-an; astro-ph.IM
Cite as:	PX:2604.00012