Properties and Chemical Evolution of the M31 Disk: Comparison with the Milky Way

TL;DR

This study models the chemical and star formation history of the M31 galaxy disk using a scaled Milky Way model, revealing discrepancies with observations that suggest additional factors influence M31's evolution.

Contribution

It introduces a modified, radial-dependent star formation rate model for M31, improving the match with observed chemical profiles compared to classical laws.

Findings

Classical star formation law does not match M31 observations.

Radial-dependent SFR improves chemical profile predictions.

Predicted SFR is higher than observed, indicating possible external influences or measurement issues.

Abstract

By adopting the chemical evolution model of the Milky Way disk, we have studied the star formation and chemical evolution history for M31 galaxy disk. We mainly concentrated on the global properties of the M31 disk. The model has been scaled to the related disk parameters, mainly the disk scale length and total disk baryon mass of M31, which we have adopted to be $r_d$=5.5kpc and $M_{tot} = 7\times 10^{10}$ \ms. It is found that, when the classical Kennicutt star formation law was applied, the obtained radial profiles of gas surface density and star formation rate (SFR) have great difference from the observed results in M31 disk. Then we have adopted modified SFR as we did for the Milky Way galaxy, that is the SFR is radial dependent. Detailed calculations show that by adjusting the star formation efficiency, it is possible to get reasonable gas and abundance profiles, but the total disk SFR is a factor of 2-3 higher than that estimated from observations. And also the predicted SFR radial profile is also much higher than what GALEX observed in the outer part. Possible reasons could be that the M31 disk has been interacted by other factors which seriously altered the star formation history, or the observed SFR is underestimated due to inappropriate extinction correction.