Diffuse Continuum Emission and Large Extended Sources at MeV Energies

Abstract Future $\gamma $ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>γ</mml:mi> </mml:math> -ray survey instruments, such as COSI , newASTROGAM and AMEGO-X , will significantly improve previous and current all-sky surveys at MeV energies. In this paper we discuss the continuum emission from the Milky Way, two prominent large extended sources, the Fermi bubbles and Loop I, and the extragalactic $\gamma $ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>γ</mml:mi> </mml:math> -ray background. We highlight the importance of measurements in the MeV to GeV energy range for understanding CR production and propagation in the Galaxy, for the determination of the nature of the Fermi bubbles and Loop I, and for exploring the origin of the extragalactic $\gamma $ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>γ</mml:mi> </mml:math> -ray background.