Distribution and kinematics of 26Al in the Galactic disc

Al-26 is a short-lived radioactive isotope thought to be injected into the interstellar medium (ISM) by massive stellar winds and supernovae (SNe). However, all-sky maps of Al-26 emission show a distribution with a much larger scale height and faster rotation speed than either massive stars or the cold ISM. We investigate the origin of this discrepancy using an N-body + hydrodynamics simulation of a Milky-Way-like galaxy, self-consistently including self-gravity, star formation, stellar feedback, and Al-26 production. We find no evidence that the Milky Way's spiral structure explains the Al-26 anomaly. Stars and the Al-26 bubbles they produce form along spiral arms, but, because our simulation produces material arms that arise spontaneously rather than propagating arms forced by an external potential, star formation occurs at arm centres rather than leading edges. As a result, we find a scale height and rotation speed for Al-26 similar to that of the cold ISM. However, we also show that a synthetic Al-26 emission map produced for a possible Solar position at the edge of a large Al-26 bubble recovers many of the major qualitative features of the observed Al-26 sky. This suggests that the observed anomalous Al-26 distribution is the product of foreground emission from the Al-26 produced by a nearby, recent SN.