Radioactive 26Al from the Scorpius-Centaurus association

Context. The Scorpius-Centaurus association is the most-nearby group of massive and young stars. As nuclear-fusion products are ejected by massive stars and supernovae into the surrounding interstellar medium, the search for characteristic gamma-ray from radioactivity is one way to probe the history of activity of such nearby massive stars on a My time scale through their nucleosynthesis. Al-26 decays with a radioactivity lifetime tau similar to 1 My, 1809 keV gamma-rays from its decay can be measured with current gamma-ray telescopes. Aims. We aim to identify nucleosynthesis ejecta from the youngest subgroup of Sco-Cen stars, and interpret their location and bulk motion from Al-26 observations with INTEGRAL's gamma-ray spectrometer SPI. Methods. Following earlier Al-26 gamma-ray mapping with NASA's Compton observatory, we test spatial emission skymaps of Al-26 for a component which could be attributed to ejecta from massive stars in the Scorpius-Centaurus group of stars. Such a model fit of spatial distributions for large-scale and local components is able to discriminate Al-26 emission associated with Scorpius-Centaurus, in spite of the strong underlying nucleosynthesis signal from the Galaxy at large. Results. We find an Al-26 gamma-ray signal above 5 sigma significance, which we associate with the locations of stars of the Sco-Cen group. The observed flux of 6 x 10(-5) ph cm(-2) s(-1) corresponds to similar to 1.1 x 10(-4) M-circle dot of Al-26. This traces the nucleosynthesis ejecta of several massive stars within the past several million years. Conclusions. We confirm through direct detection of radioactive Al-26 the recent ejection of massive-star nucleosynthesis products from the Sco-Cen association. Its youngest subgroup in Upper Scorpius appears to dominate Al-26 contributions from this association. Our Al-26 signal can be interpreted as a measure of the age and richness of this youngest subgroup. We also estimate a kinematic imprint of these nearby massive-star ejecta from the bulk motion of Al-26 and compare this to other indications of Scorpius-Centaurus massive-star activity.