Gamma-ray line signals from²⁶Al and⁶⁰Fe in the galaxies of the local group

Steady state γ-line fluxes from the decay of ²⁶Al and ⁶⁰Fe situated in the Local Group galaxies LMC, SMC, NGC 6822, IC 1613, M31, and M33 are estimated with standard supernova yields and supernova rates based on blue luminosities and other indicators of massive star formation. The largest ²⁶Al flux, 2.0 × 10^-6 γ s^-1 cm^-2, comes from the LMC, while the SMC is estimated to provide an ²⁶Al flux of 3.6 × 10^-7 γ s^-1 cm^-2. Andromeda is surprisingly weak, only about 1.6 × 10^-8 γ s^-1 cm^-2 because of both its distance and its current low rate of star formation. Expected ⁶⁰Fe fluxes are about 16% of the ²⁶Al flux. Detection of these fluxes is feasible but will probably require sensitivities greater than those of the International Gamma-Ray Astrophysical Laboratory mission. The chief utility of such observations is the new insight they provide into the mechanisms of supernova explosions, the distribution and nature of massive-star-forming regions in irregular and spiral galaxies, and the nucleosynthetic history of Local Group members.