Investigation of cosmic ray penetration with wavelet cross-correlation analysis

TL;DR

This study uses wavelet cross-correlation analysis of Fermi and Planck data to investigate cosmic ray penetration in giant molecular clouds, revealing that high-energy cosmic rays penetrate freely and have uniform distribution at parsec scales.

Contribution

It introduces a wavelet-based method to analyze cosmic ray penetration in molecular clouds using gamma-ray and dust data, providing new insights into cosmic ray behavior.

Findings

Cosmic rays above 10 GeV penetrate GMCs freely.

Gamma ray and dust maps show correlation coefficients > 0.9 at scales > 0.4 degrees.

Cosmic ray distribution is uniform down to parsec scales.

Abstract

Aims. We use Fermi and Planck data to calculate the cross correlation between gamma ray signal and gas distribution in different scales in giant molecular clouds (GMC). Then we investigate the cosmic rays (CRs) penetration in GMCs with these informations. Methods.We use the wavelet technique to decompose both the gamma ray and dust opacity maps in different scales, then we calculate the wavelet cross correlation functions in these scales. We also define wavelet response as an analog to the impulsive response in Fourier transform and calculate that in different scales down to Fermi angular resolution. Results. The gamma ray maps above 2 GeV show strong correlation with the dust opacity maps, the correlation coefficient is larger than 0.9 above a scale of 0.4 degree.The derived wavelet response is uniform in different scales. Conclusions. We argue that the CR above 10 GeV can penetrate the giant molecular cloud freely and the CRs distributions in the same energy range are uniform down to parsec scale.