The effect of radial gas flows on the chemical evolution of the Milky Way and M31

TL;DR

This study models the chemical evolution of the Milky Way and M31 considering radial gas flows, revealing their significant impact on abundance gradients and the galactic habitable zone, with implications for planet habitability.

Contribution

It introduces detailed chemical evolution models including radial gas flows and computes the galactic habitable zones for the first time with these flows considered.

Findings

Radial gas flows help reproduce observed abundance gradients.

Radial flows increase the predicted number of habitable planets.

Maximum habitability occurs at 8 kpc from the Galactic center.

Abstract

We present detailed chemical evolution models for the Milky Way and M31 in presence of radial gas flows. These models follow in detail the evolution of several chemical elements (H, He, CNO, $\alpha$ elements, Fe-peak elements) in space and time. The contribution of supernovae of different type to chemical enrichment is taken into account. We find that an inside-out formation of the disks coupled with radial gas inflows of variable speed can reproduce very well the observed abundance gradients in both galaxies. We also discuss the effects of other parameters, such as a threshold in the gas density for star formation and efficiency of star formation varying with galactic radius. Moreover, for the first time we compute the galactic habitable zone in our Galaxy and M31 in presence of radial gas flows. The main effect is to enhance the number of stars hosting a habitable planet with respect to the models without radial flow, in the region of maximum probability for this occurrence. In the Milky Way the maximum number of stars hosting habitable planets is at 8 kpc from the Galactic center, and the model with radial gas flows predicts a number of planets which is 38% larger than that predicted by the classical model.