Local patch analysis of ACT DR6 convergence map using morphological statistics

Abstract

We perform a comprehensive hierarchical, multiscale morphological analysis to search for anomalous behavior in the large-scale matter distribution, using the convergence map from the Atacama Cosmology Telescope Data Release 6 (ACT DR6). Our analysis employs a suite of morphological statistics, including Minkowski functionals, contour Minkowski tensors, and Betti numbers, and measures their deviations from ensemble expectations and median values obtained from isotropic ΛCDM (cold dark matter) simulations provided by ACT. To assess the statistical significance of these deviations, we develop a general methodology based on the persistence of anomalies across threshold ranges and spatial resolutions, while accounting for correlations among the statistics. Analyzing both the full dataset and hemispherical subregions, we find overall consistency with isotropic ΛCDM expectations. Recognizing that potential deviations in smaller sky regions may be diluted when averaged over larger areas, we further examine localized sky patches. This patchwise analysis identifies several regions exhibiting statistically significant deviations, which we designate as anomalous. In particular, we find that positive density fluctuations near the CMB Cold Spot are anomalous, exceeding 99% confidence level. This region also overlaps with a previously reported anomalous southern spot in the Planck CMB temperature data. Analysis of the corresponding null map indicates potential contamination from residual foregrounds or instrumental systematics. We also compare the anomalous patches identified in ACT data with those from a previous analysis of the Planck convergence map. No overlapping anomalous regions are found between the two datasets, suggesting that the anomalies in the Planck data are likely attributable to noise. Further investigation of these atypical patches, considering the role of residual foregrounds, instrumental systematics, reconstruction noise, and independent large-scale structure surveys, is warranted to determine their physical origin.