Evidence of Early Enrichment of the Galactic Disk by Large-Scale Winds

TL;DR

This paper presents evidence that large-scale winds played a significant role in early Galactic disk enrichment, influencing the metallicity gradient evolution and supporting a combined wind and infall model for chemical evolution.

Contribution

It introduces a 'wind+infall' model explaining the evolution of the Galactic metallicity gradient, emphasizing the impact of large-scale winds on disk chemical enrichment.

Findings

The abundance gradient steepened due to early large-scale winds.

Gradual metallicity reduction in the inner disk after wind phase.

Flattening of the gradient aligns with the wind+infall model.

Abstract

Large-scale homogeneous surveys of Galactic stars may indicate that the elemental abundance gradient evolves with cosmic time, a phenomenon that was not foreseen in existing models of Galactic chemical evolution (GCE). If the phenomenon is confirmed in future studies, we show that this effect, at least in part, is due to large-scale winds that once enriched the disk. These set up the steep abundance gradient in the inner disk (R <14 kpc). At the close of the wind phase, chemical enrichment through accretion of metal-poor material from the halo onto the disk gradually reduced the metallicity of the inner region, whereas a slow increase in the metallicity proceeded beyond the solar circle. Our "wind+infall" model accounts for flattening of the abundance gradient in the inner disk, in good agreement with observations. Accordingly, we propose that enrichment by large-scale winds is a crucial factor for chemical evolution in the disk. We anticipate that rapid flattening of the abundance gradient is the hallmarks of disk galaxies with significant central bulges.