Spectral and intensity variations of Galactic Al emission

¹ Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany e-mail: wwang@mpe.mpg.de
² National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, PR China
³ AstroParticule et Cosmologie (APC), 11 place Marcelin Berthelot, 75231 Paris, France
⁴ Centre d'Étude Spatiale des Rayonnements, BP 4346, 31028 Toulouse Cedex 4, France
⁵ ESA-ESTEC, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands

Received: 17 October 2008
Accepted: 28 January 2009

Abstract

Aims. 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.

Methods. 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.

Results. We detect the ²⁶Al line from the inner Galaxy at ~ significance. The line appears narrow, and we constrain broadening in the source regions to <1.3 keV (). Different sky distribution models do not significantly affect those large-scale results. The ²⁶Al intensity for the inner Galaxy is derived as   , consistent with earlier results from COMPTEL and SPI data. This can be translated to an ²⁶Al mass of 2.7 ± 0.7  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 () appears somewhat broadened. Latitudinal variations of ²⁶Al emission towards the inner Galaxy are studied, finding a latitudinal scale height of  pc for ²⁶Al in the inner Galaxy and a hint (3σ) of peculiar ²⁶Al emission towards the region , .