Galactic Rotation seen in the 26 Al line by INTEGRAL

In a recent article in Nature (published January 5 2006) Diehl et al. 
present observations on the Galactic Centre obtained with the SPI 
instrument onboard INTEGRAL. The exposure time at the Galactic Center 
is 4 Ms.

The picture shows at the left the line profiles obtained at different
locations; a clear shift in the line centroid in the top and bottom
panels compared to the center panel (l = 0) is visible. Detailed
modelling shows that the shift is fully consistent with the Doppler
shift of the line energy (1809 keV) expected from the galactic
rotation. The map on the right shows this expectaction based on
modelling the Galactic rotation curve and a 3-dimensional distribution
of 26 Al sources. The observed line shift is less than 0.5 keV,
demonstrating the superb quality of SPI's spectral resolution
capabilities. The dominant sources of 26 Al emission are massive
stars. This observation shows that 26 Al emission is truly global, as
we see the entire amount of it throughout our Galaxy and co-rotate with
the Galaxy.

From this observation Diehl et al. determine a present-day equilibrium mass
of 2.8 +/- 0.8 solar masses of 26 Al. In addition, this observation allows 
to independently estimate the frequency of core-collapse supernovae in our 
Galaxy to be 1.9 +/- 1.1 events per century.

Credits: R. Diehl (MPE, Garching Germany)