Doppler shift of the 1.8 MeV gamma-ray line from 26Al due to large-scale galactic rotation
The velocity of the interstellar gas harboring radioactive 26Al can be observed through Doppler shifts of the 26Al line energy (E0 = 1808.6 keV).
Here we show measurements along the line of sight towards the inner Galaxy, where the large-scale Galactic rotation imprints this characteristic wave-like shape of velocity offset versus Galactic longitude. This has been observed for molecular and atomic gas in our and other galaxies. But with 26Al gamma-rays, we get unique access to the tenuous, diluted, and presumably hot phase of the interstellar medium, as it is expected around the massive stars which eject radioactive 26Al.
(Kretschmer et al., in preparation, The SPI Team 2010).
