The Galactic26al Emission Map as Revealed Byintegralspi

Diffuse emission is often challenging since it is undetectable by most instruments, which are generally dedicated to point-source studies. The 26 Al emission is a good illustration: the only available 26 Al map to date has been released, more than 15 yr ago, thanks to the COMPTEL instrument. However, at the present time, the SPI spectrometer aboard the International Gamma-Ray Astrophysics Laboratory mission offers a unique opportunity to enrich this first result. In this paper, 2 × 10 8 s of data accumulated between 2003 and 2013 are used to perform a dedicated analysis, aiming to deeply investigate the spatial morphology of the 26 Al emission. The data are first compared with several sky maps based on observations at various wavelengths to model the 26 Al distribution throughout the Galaxy. For most of the distribution models, the inner Galaxy flux is compatible with a value of 3.3 × 10 −4 photons cm −2 s −1 , while the preferred template maps correspond to young stellar components such as core-collapse supernovae (SNe), Wolf–Rayet stars, and massive AGB stars. To get more details about this emission, an image reconstruction is performed using an algorithm based on the maximum-entropy method. In addition to the inner Galaxy emission, several excesses suggest that some sites of emission are linked to the spiral arm structure. Lastly, an estimation of the 60 Fe line flux, assuming a spatial distribution similar to 26 Al line emission, results in a 60 Fe-to- 26 Al ratio around 0.14, which agrees with the most recent studies and with the SN explosion model predictions.