The Effects of radial inflow of gas and galactic fountains on the chemical evolution of M31

TL;DR

This study investigates how galactic fountains and radial gas flows influence the chemical evolution of M31's disk, finding that radial flows and inside-out formation are key to explaining observed abundance gradients.

Contribution

The paper introduces a ballistic method to assess galactic fountains' effects and demonstrates that radial gas flows combined with inside-out formation explain M31's chemical gradients.

Findings

Galactic fountains have negligible impact on M31's chemical evolution.

Radial gas flows with variable speed reproduce observed abundance gradients.

Inside-out disk formation is crucial for chemical gradient development.

Abstract

Galactic fountains and radial gas flows are very important ingredients in modeling the chemical evolution of galactic disks. Our aim here is to study the effects of galactic fountains and radial gas flows in the chemical evolution of the disk of M31. We adopt a ballistic method to study the effects of galactic fountains on the chemical enrichment of the M31 disk. We find that the landing coordinate for the fountains in M31 is no more than 1 kpc from the starting point, thus producing negligible effect on the chemical evolution of the disk. We find that the delay time in the enrichment process due to fountains is no longer than 100 Myr and this timescale also produces negligible effects on the results. Then, we compute the chemical evolution of the M31 disk with radial gas flows produced by the infall of extragalactic material and fountains. We find that a moderate inside-out formation of the disk coupled with radial flows of variable speed can very well reproduce the observed gradient. We discuss also the effects of other parameters such a threshold in the gas density for star formation and an efficiency of star formation varying with the galactic radius. We conclude that the most important physical processes in creating disk gradients are the inside-out formation and the radial gas flows. More data on abundance gradients both locally and at high redshift are necessary to confirm this conclusion.