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 (RG ≳ 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-AV -limited samples in the two clusters, from which IMFs were derived by model-fitting the F200W band luminosity function, resulting in IMF peak masses (hereafter MC ) log MC /M⊙ ≃ −1.5 ± 0.5 for both clusters. Although the uncertainties are rather large, the obtained MC values are lower than those in any previous study (log MC /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 MC is also consistent with the theoretical expectation of the lower Jeans mass due to the higher gas density under such low metallicity. The MC values derived from observations in such an environment would place significant constraints on the understanding of star formation.