Gamma-ray spectroscopy of galactic nucleosynthesis

TL;DR

This paper uses gamma-ray spectroscopy to study nucleosynthesis in our galaxy, focusing on radioactive $^{26}$Al decay, and employs population synthesis of massive stars to predict gamma-ray emissions, revealing insights into stellar feedback and distribution.

Contribution

It refines a population synthesis method to predict gamma-ray sky maps from massive star groups using stellar evolution models and observations, highlighting the distribution and feedback of nucleosynthesis sources.

Findings

Support for a clumpy distribution of gamma-ray sources across the galaxy.

Evidence of large cavities around massive star groups affecting gamma-ray emission.

Discrepancy suggests additional $^{26}$Al emission from nearby cavities.

Abstract

Diffuse gamma-ray emission from the decay of radioactive $^{26}$Al is a messenger from the nucleosynthesis activity in our current-day galaxy. Because this material is attributed to ejections from massive stars and their supernovae, the gamma-ray signal includes information about nucleosynthesis in massive star interiors as it varies with evolutionary stages, and about their feedback on the surrounding interstellar medium. Our method of population synthesis of massive-star groups has been refined as a diagnostic tool for this purpose. It allows to build a bottom-up prediction of the diffuse gamma-ray sky when known massive star group distributions and theoretical models of stellar evolution and core-collapse supernova explosions are employed. We find general consistency of an origin in such massive-star groups, in particular we also find support for the clumpy distribution of such source regions across the Galaxy, and characteristics of large cavities around these. A discrepancy in the integrated $^{26}$Al gamma-ray flux is interpreted as an indication for excess $^{26}$Al emission from nearby, distributed in cavities that extend over major regions of the sky.