Clustering of Local Extrema in Planck CMB maps

Abstract

The clustering of local extrema will be exploited to examine Gaussianity, asymmetry, and the footprint of the cosmic-string network on the CMB observed by Planck. The number density of local extrema ($n_{\rm pk}$ for peak and $n_{\rm tr}$ for trough) and sharp clipping ($n_{\rm pix}$) statistics support the Gaussianity hypothesis for all component separations. However, the pixel at the threshold reveals a more consistent treatment with respect to end-to-end simulations. A very tiny deviation from associated simulations in the context of trough density, in the threshold range $θ\in [-2-0]$ for NILC and CR component separations, are detected. The unweighted two-point correlation function, of the local extrema, illustrates good consistency between different component separations and corresponding Gaussian simulations for almost all available thresholds. However, for high thresholds, a small deficit in the clustering of peaks is observed with respect to the Planck fiducial $Λ$CDM model. To put a significant constraint on the amplitude of the mass function based on the value of $Ψ$ around the Doppler peak ($θ\approx 70-75$ arcmin), we should consider $\vartheta\lesssim 0.0$. The scale-independent bias factors for the peak above a threshold for large separation angle and high threshold level are in agreement with the value expected for a pure Gaussian CMB. Applying the $n_{\rm pk}$, $n_{\rm tr}$, $Ψ_{\rm pk-pk}$ and $Ψ_{\rm tr-tr}$ measures on the tessellated CMB map with patches of $7.5^2$ deg$^2$ size prove statistical isotropy in the Planck maps. The peak clustering analysis puts the upper bound on the cosmic-string tension, $Gμ^{(\rm up)} \lesssim 5.59\times 10^{-7}$, in SMICA.