Investigate the GeV gamma-ray emissions from the Perseus molecular cloud

ABSTRACT We study the GeV gamma-ray emissions toward the dense cores IC 348, NGC 1333, and Barnard 1 (B1) with a scale of about 5 pc in the Perseus molecular cloud (MC) using the Fermi Large Area Telescope. We reconstruct a background model and find that the column density distribution of molecular hydrogen (H2) + neutral atomic hydrogen (H i) + dark gas template provides the best-fitting template for spatial analysis, which supports a hadronic origin of the gamma-ray emissions from the dense cores in the Perseus MC. All three cores exhibit hard gamma-ray spectra (photon index ∼2.3), which are consistent with those of young massive star clusters. The gamma-ray spectra of IC 348 and B1 are higher than those derived from the local cosmic rays (CRs), likely originating from inelastic interactions between protons accelerated by massive stellar winds and ambient gas. The gamma-ray spectrum of NGC 1333 exhibits a slight excess above 2 GeV, but a slight deficit below 2 GeV when compared to the spectrum derived from the local CRs. We argue that the suppression of the CR spectrum in NGC 1333 is probably caused by the slow diffusion of CRs, and the distinct characteristic compared to the other two cores may be linked to its nature as a reflection nebula.