2009A&A...496..713W

Gamma-ray line emission from the radioactive decay of ²⁶Al reflects nucleosynthesis in massive stars and supernovae. We use INTEGRAL ²⁶Al measurements to characterize the distribution and characteristics of ²⁶Al source regions throughout the Galaxy. The spectrometer SPI aboard INTEGRAL has accumulated over five years of data on ²⁶Al gamma-ray emission from the Galactic plane. We analyzed these data using suitable instrumental-background models and adopted sky distribution models to produce high-resolution ²⁶Al spectra of Galactic emission, spatially resolved along the Galaxy plane. We detect the ²⁶Al line from the inner Galaxy at ∼28σ significance. The line appears narrow, and we constrain broadening in the source regions to <1.3keV (2σ). Different sky distribution models do not significantly affect those large-scale results. The ²⁶Al intensity for the inner Galaxy is derived as (2.9±0.2)x10^–4ph/cm2/s/rad, consistent with earlier results from COMPTEL and SPI data. This can be translated to an ²⁶Al mass of 2.7±0.7 M_☉ in the Galaxy as a whole. The ²⁶Al intensity is also confirmed to be somewhat brighter in the 4th than in the 1st quadrant (ratio ∼1.3±0.2). ²⁶Al spectra separately derived for regions along the Galactic plane show clear line centroid shifts, attributed largely to the Galaxy's large-scale rotation. The ²⁶Al line toward the direction of the Aquila region (20°< l < 40°) appears somewhat broadened. Latitudinal variations of ²⁶Al emission towards the inner Galaxy are studied, finding a latitudinal scale height of 130⁺¹²⁰_–70pc (1σ) for ²⁶Al in the inner Galaxy and a hint (3σ) of peculiar ²⁶Al emission towards the region l<0°, b>5°.