Diffuse Galactic Gamma Rays at intermediate and high latitudes. I. Constraints on the ISM properties

TL;DR

This study uses Fermi gamma-ray data and the DRAGON code to constrain the properties of the interstellar medium and cosmic ray propagation in the Galaxy, with implications for dark matter detection.

Contribution

It provides new constraints on ISM gas distribution and cosmic ray diffusion parameters by combining gamma-ray and cosmic ray spectral analyses.

Findings

Constraints on the vertical scale height of cosmic ray diffusion.

Insights into the distribution of HI and H2 gas in the ISM.

Discussion of the spectral break at ~230 GV in cosmic rays.

Abstract

We study the high latitude (|b|>10) diffuse gamma-ray emission in the Galaxy in light of the recently published data from the Fermi collaboration at energies between 100 MeV and 100 GeV. The unprecedented accuracy in these measurements allows to probe and constrain the properties of sources and propagation of cosmic rays (CRs) in the Galaxy, as well as confirming conventional assumptions made on the interstellar medium (ISM). Using the publicly available DRAGON code, that has been shown to reproduce local measurements of CRs, we study assumptions made in the literature on HI and H2 gas distributions in the ISM, and non spatially uniform models of diffusion in the Galaxy. By performing a combined analysis of CR and gamma-ray spectra, we derive constraints on the properties of the ISM gas distribution and the vertical scale height of galactic CR diffusion, which may have implications also on indirect Dark Matter detection. We also discuss some of the possible interpretations of the break at ~230 GV in CR protons and helium spectra, recently observed by PAMELA and their impact on gamma-rays.