Cluster Morphology as a Systematic in ISW Measurements: Evidence from Planck SZ Clusters and SZ-Free CMB Maps

We test whether the dynamical state of galaxy clusters correlates with the Integrated Sachs-Wolfe (ISW) temperature signal measured at their locations. Using 942 confirmed clusters from the Planck PSZ2 catalogue with the Planck SMICA SZ-free CMB map, we classify clusters as relaxed or disturbed based on their residual from the Y_SZ–mass scaling relation. Disturbed clusters show a mean CMB temperature of −5.1 μK while relaxed clusters show +2.0 μK, yielding a difference of −7.1 ± 3.4 μK (2.1σ, p = 0.037). The signal survives mass matching (364 pairs, −6.5 μK, 1.7σ) and is concentrated at z < 0.2, with the strongest signal at z = 0.10–0.15 (−28.7 μK, 2.8σ, p = 0.006). The sign and redshift dependence are consistent with the anomalous negative ISW effect reported by Hansen et al. (2026). Code: https://github.com/alikamp/Parks-ISW-Morphology