Revealing Potential Initial Mass Function variations with metallicity: JWST observations of young open clusters in a low-metallicity environment

We present the substellar mass function of star-forming clusters (0.1 Myr old) in a low-metallicity environment (-$0.7 dex). We performed deep JWST/NIRCam and MIRI imaging of two star-forming clusters in Digel Cloud 2, a star-forming region in the Outer Galaxy ($R_G 15$ kpc). The very high sensitivity and spatial resolution of JWST enable us to resolve cluster members clearly down to a mass detection limit of 0.02 $M_$, enabling the first detection of brown dwarfs in low-metallicity clusters. Fifty-two and ninety-one sources were extracted in mass-$A_V$-limited samples in the two clusters, from which Initial mass functions (IMFs) were derived by model-fitting the F200W band luminosity function, resulting in IMF peak masses (hereafter $M_C$) $log M_C / M_ -1.5 ± 0.5$ for both clusters. Although the uncertainties are rather large, the obtained $M_C$ values are lower than those in any previous study ($log M_C / M_ ~ -0.5$). Comparison with the local open clusters with similar ages to the target clusters ($~10⁶-10⁷ yr) suggests a metallicity dependence of MC, with lower MC at lower metallicities, while the comparison with globular clusters, similarly low metallicities but considerably older (~10¹⁰$ yr), suggests that the target clusters have not yet experienced significant dynamical evolution and remain in their initial physical condition. The lower $M_C$ is also consistent with the theoretical expectation of the lower Jeans mass due to the higher gas density under such low metallicity. The $M_C$ values derived from observations in such an environment would place significant constraints on the understanding of star formation.