Protoplanetary Disk Evolution in a Low-metallicity Environment: JWST’s First Mid-infrared Census of Low-mass Stars

Abstract This study presents the first high-resolution, high-sensitivity mid-infrared (MIR) investigation of protoplanetary disks in a low-metallicity environment, using JWST/NIRCam and MIRI observations of Digel Cloud 2, a star-forming region in the outer Galaxy ( D ≃ 8 kpc, [M/H] ≃ –0.7 dex). It hosts two very young (∼0.1 Myr) embedded clusters, Cloud 2-N and Cloud 2-S, offering a window into disk evolution under conditions analogous to the early Universe, where low metallicity implies reduced dust content. Imaging across 1–20 μ m, including F770W and complementary bands (F356W, F444W, F405N), enables probing disk properties with unprecedented spatial resolution and stellar mass sensitivity down to ∼0.1 M ⊙ . Among 89 and 95 sources detected in F770W in Cloud 2-N and 2-S, respectively, we identify candidate stellar-mass cluster members using infrared photometry, from which stellar mass and extinction are estimated. Among these, ≃75% retain optically thick disks in both clusters based on MIR spectral energy distribution slopes, consistent with similarly aged solar-metallicity regions. In contrast, a lack of 2 μ m excess suggests diminished inner disk emission, possibly due to enhanced silicate grains with low sublimation temperatures. Using the F405N narrowband filter covering Br α , we detect accretion signatures in ≃35% of sources selected by extinction criteria, with rates ≳10 −6 M ⊙ yr −1 , comparable to or exceeding those in nearby low-mass stars. Brown dwarf candidates, identified across multiple bands including F770W and shorter wavelengths, exhibit a high disk fraction of ∼75%, indicating robust disk retention across mass ranges even under low-metallicity conditions.