Galactic 26Al traces metal loss through hot chimneys

TL;DR

This study uses simulations to show that radioactive 26Al traces metal ejection through hot chimneys in galaxies, revealing how metals are distributed into hot outflows and cold gas, impacting galaxy evolution models.

Contribution

It introduces a simulation of a Milky-Way-like galaxy demonstrating the distribution of 26Al into hot and cold channels, highlighting the role of hot chimneys in metal transport.

Findings

30-40% of 26Al remains hot with Gyr cooling times

26Al traces chimney-fed outflows into the galaxy halo

Hot and cold metal ejection ratios align with chemical evolution models

Abstract

Radioactive 26Al is an excellent tracer for metal ejection in the Milky Way, and can provide a direct constraint on the modelling of supernova feedback in galaxy evolution. Gamma-ray observations of the 26Al decay line have found high velocities and hence require a significant fraction of the Galactic 26Al in the hot component. At the same time, meteoritic data combined with simulation results suggest that a significant amount of 26Al makes its way into stars before decay. We investigated the distribution into hot and cold channels with a simulation of a Milky-Way-like galaxy with massive-star feedback in superbubbles and with ejecta traced by 26Al. About 30-40 per cent of the ejecta remain hot, with typical cooling times of the order Gyr. 26Al traces the footpoints of a chimney-fed outflow that mixes metals turbulently into the halo of the model galaxy on a scale of at least 50 kpc. The rest diffuses into cold gas with temperatures less than about 10,000 K, and may therefore be quickly available for star formation. We discuss the robustness of the result by comparison to a simulation with a different global flow pattern. The branching ratio into hot and cold components is comparable to that of longer term average results from chemical evolution modelling of galaxies, clusters and the intracluster medium.