THE GALACTIC 26AL EMISSION MAP AS REVEALED BY INTEGRAL SPI

Diffuse emission is often challenging since it is undetectable by most instruments, which are generally dedicated to point-source studies. The Al-26 emission is a good illustration: the only available Al-26 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 x 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 Al-26 emission. The data are first compared with several sky maps based on observations at various wavelengths to model the Al-26 distribution throughout the Galaxy. For most of the distribution models, the inner Galaxy flux is compatible with a value of 3.3 x 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 Fe-60 line flux, assuming a spatial distribution similar to Al-26 line emission, results in a Fe-60-to-Al-26 ratio around 0.14, which agrees with the most recent studies and with the SN explosion model predictions.