INTEGRAL SPI all-sky view in soft gamma rays:: A study of point-source and Galactic diffuse emission

We have processed the data accumulated with the INTEGRAL SPI instrument over 4 years (similar to 51 Ms) to study the morphology of the Galactic "diffuse'' emission in the 20 keV to 8 MeV energy range. To achieve this, we simultaneously derived an all-sky census of emitting sources and images of the Galactic ridge (GR) emission. In the central radian, the resolved point-source emission amounts to 88%, 91%, and 68% of the total in the 25-50, 50-100, and 100-300 keV domains, respectively. We compare the spatial distribution of the GR emission with the distributions obtained from CO and near-IR maps and quantify our results through latitude and longitude profiles. Below 50 keV, the SPI data are better traced by the latter, supporting a stellar origin for this emission. Furthermore, we find that the GR emission spectrum follows a power law with a photon index similar to 1.55 above 50 keV, while an additional component is required below that energy. This component shows a cutoff around 30 keV, reinforcing a stellar origin, as proposed by Krivonos et al. The component of the diffuse emission due to e(+/-) annihilations is extracted simultaneously, leading to the determination of the related parameters (positronium flux and fraction). Specific discussion is devoted to the annihilation-line distribution, since significant emission is detected over a region as large as similar to 80 degrees; similar to 10 degrees, potentially associated with the disk or halo surrounding the central regions of our Galaxy.