Chemical evolution of $^{26}$Al and $^{60}$Fe in the Milky Way

TL;DR

This paper models the chemical evolution of $^{26}$Al and $^{60}$Fe in the Milky Way, comparing theoretical predictions with observations to identify dominant sources and estimate current isotope masses and injection rates.

Contribution

It introduces a detailed chemical evolution model incorporating various stellar yields to predict isotope masses and sources in the Galaxy, aligning with observations for $^{26}$Al.

Findings

Massive stars are the main source of $^{26}$Al and $^{60}$Fe.

Novae are necessary to reproduce observed $^{26}$Al levels.

Predicted $^{26}$Al mass is 2.12 M$_{ ext{☉}}$, matching observations.

Abstract

We present theoretical mass estimates of $^{26}$Al and $^{60}$Fe throughout the Galaxy, performed with a numerical chemical evolution model including detailed nucleosynthesis prescriptions for stable and radioactive nuclides. We compared the results for several sets of stellar yields taken from the literature, for massive, low and intermediate mass stars, nova systems (only for $^{26}$Al) and supernovae Type Ia.We then computed the total masses of $^{26}$Al and $^{60}$Fe in the Galaxy. We studied the bulge and the disc of the Galaxy in a galactocentric radius range 0-22 kpc. We assumed that the bulge region (within 2 kpc) evolved quickly suffering a strong star formation burst, while the disc formed more slowly and inside-out. We compared our results with the $^{26}$Al mass observed by the $\gamma$-ray surveys COMPTEL and INTEGRAL to select the best model. Concerning $^{60}$Fe, we do not have any observed mass value so we just performed a theoretical prediction for future observations. In conclusion, low, intermediate mass stars and Type Ia supernovae contribute negligibly to the two isotopes, while massive stars are the dominant source. The nova contribution is, however, necessary to reproduce the observations of $^{26}$Al. Our best model predicts $2.12$ M$_{\odot}$ of $^{26}$Al, in agreement with observations, while for $^{60}$Fe our best mass estimate is $\sim 1.05$ M$_{\odot}$. We also predicted the present injection rate of $^{26}$Al and $^{60}$Fe in the Galaxy and compared it with previous results, and we found a larger present time injection rate along the disc.