Searching For Distant Brown Dwarfs In Deep JWST Fields

Low-mass stars and brown dwarfs (ultracool dwarfs, UCDs, <0.1 solar mass, Teff < 3000 K) constitute a significant fraction of the Galaxy's stellar population, estimated at around 25%. Despite their high abundance, UCDs are intrinsically faint, limiting studies to the immediate solar neighborhood (<100 pc). The James Webb telescope's deep spectroscopic surveys enable the detection of distant objects at >1 kpc, allowing us to study their Galactic distribution. In this study, we used a library of ~2,000 nearby UCD low-resolution spectra to identify UCDs in the Parallel Application of Slitless Spectroscopy to Analyze Galaxy Evolution (PASSAGE) survey data. By measuring flux ratios between narrow wavelength bands covering 1.3-1.7 microns, we evaluated the effectiveness of these features in distinguishing brown dwarfs from galaxies and other point sources in the survey. Although we did not identify any UCD candidates with spectral types in this analysis, we remain hopeful that further investigation will yield promising results.