The Galactic ${}^{26}$Al emission map as revealed by INTEGRAL/SPI

Abstract

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 fifteen years ago, thanks to the COMPTEL instrument. However, at the present time, the SPI spectrometer aboard the INTEGRAL mission offers a unique opportunity to enrich this first result. In this paper, 2 $\times$ 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$\times$ 10${}^{-4}$ ph.cm${}^{-2}$.s${}^{-1}$ while the preferred template maps correspond to young stellar components such as core-collapse supernovae, Wolf-Rayet 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 arms 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.

arXiv comment12 pages, 9 figures, 3 tables. Accepted for publication in The Astrophysical Journal

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