Spectral And Intensity Variations Of Galactic Al-26 Emission

Aims. Gamma-ray line emission from the radioactive decay of Al-26 reflects nucleosynthesis in massive stars and supernovae. We use INTEGRAL Al-26 measurements to characterize the distribution and characteristics of Al-26 source regions throughout the Galaxy.Methods. The spectrometer SPI aboard INTEGRAL has accumulated over five years of data on Al-26 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 Al-26 spectra of Galactic emission, spatially resolved along the Galaxy plane.Results. We detect the Al-26 line from the inner Galaxy at similar to 28 sigma significance. The line appears narrow, and we constrain broadening in the source regions to <1.3 keV (2 sigma). Different sky distribution models do not significantly affect those large-scale results. The Al-26 intensity for the inner Galaxy is derived as (2.9 +/- 0.2) x 10(-4) ph cm(-2) s(-1) rad(-1), consistent with earlier results from COMPTEL and SPI data. This can be translated to an Al-26 mass of 2.7 +/- 0.7 M-circle dot in the Galaxy as a whole. The Al-26 intensity is also confirmed to be somewhat brighter in the 4th than in the 1st quadrant (ratio similar to 1.3 +/- 0.2). Al-26 spectra separately derived for regions along the Galactic plane show clear line centroid shifts, attributed largely to the Galaxy's large-scale rotation. The Al-26 line toward the direction of the Aquila region (20 degrees < l < 40 degrees) appears somewhat broadened. Latitudinal variations of Al-26 emission towards the inner Galaxy are studied, finding a latitudinal scale height of 130(-70)(+120) pc (1 sigma) for Al-26 in the inner Galaxy and a hint (3 sigma) of peculiar Al-26 emission towards the region l < 0 degrees, b > 5 degrees.