Can Cosmic Rays Interacting With Molecular Clouds Explain The Galactic Center Gamma-Ray Excess?

TL;DR

This paper investigates whether cosmic rays interacting with molecular clouds can explain the gamma-ray excess observed at the Galactic Center, concluding that multiple sources including dark matter and pulsars are likely involved.

Contribution

It demonstrates that cosmic-ray interactions alone cannot fully account for the gamma-ray excess, suggesting a combination of sources is necessary.

Findings

Gamma-ray excess best fit by combined NFW and Galactic Ridge templates

Cosmic-ray model alone cannot explain all excess gamma rays

Spectral analysis remains consistent with previous models

Abstract

The Fermi Large Area Telescope data appear to have an excess of gamma rays from the inner 150 pc of the Galactic Center (GC). The main explanations proposed for this are: an unresolved population of millisecond pulsars (MSPs), dark matter (DM) annihilation, and cosmic rays interacting with molecular clouds at the GC. In this conference proceeding article we highlight some of the cosmic-ray results of [1]. The MSPs and DM explanations were modeled with spatial templates well fitted by the square of a generalized Navarro-Frenk-White (NFW) profile with inner slope $\gamma=1.2$. The cosmic-ray option was modeled with a 20-cm continuum emission Galactic Ridge template. A template based on the HESS residuals were shown to give similar results. The gamma-ray excess was found to be best fit by a combination of the generalized NFW squared template and a Galactic Ridge template. We also found the spectra of each template was not significantly affected in the combined fit and is consistent with previous single template fits. Due to the ridge like morphology of the molecular gas at the GC, the cosmic-ray option was not able to explain all the excess gamma rays, indicating that DM annihilation and/or an unresolved population of MSPs is also needed.