Constraining the cosmic ray propagation halo thickness using Fermi-LAT observations of high-latitude clouds
Abstract
As a basic characteristic of cosmic ray (CR) propagation, the diffusive halo can advance our understanding of many CR-related studies and indirect dark matter. The method to derive the halo size usually has degeneracy problems thus affected by large uncertainties. The diffusion gamma ray from high-latitude clouds might shed light on the halo size independently. Since the spatially dependent propagation (SDP) model has a better agreement with the observed CRs, compared with conventional propagation model, in this work, we investigate the halo thickness based on SDP model with Fermi-LAT γ-ray observation on the high- and intermediate-velocity clouds. As a result, in order not to exceed the relative γ-ray emissivity in the high-latitude clouds, halo thickness should be in the range of ~3.39~ kpc. Moreover, the spatial morphology of γ-rays estimated based on SDP model under different values of halo thickness are distinctive, which provides us a tool to determine the halo size. We hope that our model could be tested and tuned by multi-wavelength observations in the future.