Monte Carlo Simulation of the Galactic26Al Gamma‐Ray Map

The observed map of 1.809 MeV gamma-rays from radioactive Al-26 (Oberlack etal, 1996) shows clear evidence of Galactic plane origin with an unevendistribution. We have simulated the map using a Monte Carlo technique togetherwith simple assumptions about the spatial distributions and yields of Al-26sources (clustered core-collapse supernovae and Wolf Rayet stars; low- andhigh-mass AGB stars; and novae). Although observed structures (e.g., tangentsto spiral arms, bars, and known star-forming regions) are not included in themodel, our simulated gamma-ray distribution bears resemblance to the observeddistribution. The major difference is that the model distribution has a strongsmooth background along the Galactic plane from distant sources in the disk ofthe Galaxy. We suggest that the smooth background is to be expected, andprobably has been suppressed by background subtraction in the observed map. Wehave also found an upper limit of 1 Msun to the contribution of flux fromlow-yield, smoothly distributed sources (low-mass AGB stars and novae).Comment: 10 pp LaTeX + 3 PostScript figures, Submitted to ApJ (1 Apr 1998