The Lifetime of Protoplanetary Disks in a Low-Metallicity Environment

TL;DR

This study investigates protoplanetary disk lifetimes in a low-metallicity environment of the outer Galaxy, finding that disks disperse faster than in the solar neighborhood, which impacts planet formation.

Contribution

It provides observational evidence that low metallicity environments lead to quicker disk dispersal, suggesting a link to the metallicity dependence of planet formation.

Findings

Lower NIR excess fraction in low-metallicity clusters

Disks disperse within less than 1 Myr in EOG environments

Shorter disk lifetimes may hinder planet formation in low-metallicity regions

Abstract

The extreme outer Galaxy (EOG), the region with a Galactic radius of more than 18 kpc, is known to have very low metallicity, about one-tenth that of the solar neighborhood. We obtained deep near-infrared (NIR) images of two very young ($\sim$0.5 Myr) star-forming clusters that are one of the most distant embedded clusters in the EOG. We find that in both clusters the fraction of stars with NIR excess, which originates from the circumstellar dust disk at radii of $\leq$0.1 AU, is significantly lower than those in the solar neighborhood. Our results suggest that most stars forming in the low-metallicity environment experience disk dispersal at an earlier stage ($<$1 Myr) than those forming in the solar metallicity environment (as much as $\sim$5--6 Myr). Such rapid disk dispersal may make the formation of planets difficult, and the shorter disk lifetime with lower metallicity could contribute to the strong metallicity dependence of the well-known "planet-metallicity correlation", which states the probability of a star hosting a planet increases steeply with stellar metallicity. The reason for the rapid disk dispersal could be increase of the mass accretion rate and/or the effective far-ultraviolet photoevaporation due to the low extinction; however, another unknown mechanism for the EOG environment could be contributing significantly.