Does Metallicity affect Protoplanetary Disk Fraction? Answers from the Outer Milky Way

TL;DR

This study investigates how metallicity influences protoplanetary disk presence in young clusters of the outer Milky Way, revealing lower disk fractions at reduced metallicities and a positive correlation between metallicity and disk fraction.

Contribution

It provides the first comprehensive analysis of disk fraction dependence on metallicity in low-metallicity clusters beyond the solar neighborhood.

Findings

Low-metallicity clusters have 2.6 times lower disk fractions than solar-metallicity clusters.

No evidence of faster disk decay in low-metallicity regions within the studied age range.

Positive correlation between metallicity and disk fraction across different age groups.

Abstract

The role of metallicity in shaping protoplanetary disk evolution remains poorly comprehended. This study analyzes the disk fraction of 10 young (0.9-2.1 Myr) and low-metallicity (0.34-0.83 Z$_{\odot}$) clusters located in the outer Milky Way with Galactocentric distances between 10 and 13 kpc. Using $JHK$ data obtained from UKIDSS, the calculated disk fraction values for low-mass stars (0.2-2 M$_{\odot}$) ranged from 42% to 7%. To enhance the statistical reliability of our analysis, eight additional low-metallicity clusters are sourced from previous studies with metallicity range 0.25-0.85 Z$_{\odot}$ along with our sample, resulting in a total of 18 regions with low-metallicity. We find that low-metallicity clusters exhibit on average $2.6\pm0.2$ times lower disk fraction compared to solar-metallicity clusters in all the age bins we have. Within the age range we can probe, our study does not find evidence of faster disk decay in sub-solar metallicity regions compared to solar-metallicity regions. Furthermore, we observe a positive correlation between cluster disk fraction and metallicity for two different age groups of 0.3-1.4 and 1.4-2.5 Myr. We emphasize that both cluster age and metallicity significantly affect the fraction of stars with evidence of inner disks.