Spectral and intensity variations of Galactic $\mathsf{^{26}}$Al emission

Abstract

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