Radial Migration from Metallicity Gradient of Open Clusters and Outliers

TL;DR

This study analyzes the metallicity gradient of open clusters to understand radial migration in the Galactic disk, revealing age-dependent migration patterns, a break in the gradient at 11.5 kpc, and complex outer disk evolution.

Contribution

It provides a comprehensive quantitative analysis of radial migration effects on open clusters, highlighting the age dependence and boundary effects in the Galactic disk.

Findings

Metallicity gradient of -0.074 dex/kpc for clusters younger than 0.5 Gyr.

Identification of three sequences of clusters corresponding to different migration histories.

Discovery of a break in the metallicity gradient at approximately 11.5 kpc.

Abstract

Radial migration is an important process in the evolution of the Galactic disk. The metallicity gradient of open clusters and its outliers provide an effective way to probe for this process. In this work, we compile metallicity, age, and kinematic parameters for 225 open clusters and carry out a quantitative analysis of radial migration via the calculated migration distances. Based on clusters with age $< 0.5$ Gyr, we obtain the present-day metallicity gradient of $-0.074 \pm 0.007$ dex/kpc. Along this gradient distributes three sequences, and clusters in the upper, the middle, and the lower groups are found to be old outward-migrators, in-situ clusters, and inward-migrators, respectively. The migration distance increases with age, but its most effective time is probably less than 3 Gyr. The metallicity gradient breaks out at $R_g$ (guiding center radius) $\sim11.5$ kpc, which is caused by the lack of young open clusters in the outer disk and the presence of old outward-migrators in the upper sequence. It shows that this boundary is related to the different effects of radial migration between the inner and outer disks. We also found many special open clusters in and near the outer disk of $R > 11$ kpc and a steeper metallicity gradient from the inner disk of $R_g < 7$ kpc, which tells a complicated evolution history of the Galactic disk by different effects of stellar radial migration.