2015ApJ...801..142B

Diffuse emission is often challenging since it is undetectable by most instruments, which are generally dedicated to point-source studies. The ²⁶Al emission is a good illustration: the only available ²⁶Al 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, 2x10⁸ s of data accumulated between 2003 and 2013 are used to perform a dedicated analysis, aiming to deeply investigate the spatial morphology of the ²⁶Al emission. The data are first compared with several sky maps based on observations at various wavelengths to model the ²⁶Al distribution throughout the Galaxy. For most of the distribution models, the inner Galaxy flux is compatible with a value of 3.3x10^–4 photons/cm2/s, 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 ⁶⁰Fe line flux, assuming a spatial distribution similar to ²⁶Al line emission, results in a ⁶⁰Fe-to-²⁶Al ratio around 0.14, which agrees with the most recent studies and with the SN explosion model predictions.