2501.16648v1
Three Brown Dwarfs Masquerading as High-Redshift Galaxies in JWST Observations
Digest
From RUBIES NIRSpec PRISM/CLEAR (0.6–5.3 μm) spectra, the authors confirm three compact RUBIES sources (o005_s41280, o006_s00089, o006_s35616) are brown dwarfs rather than distant galaxies. Sonora Elf Owl fits yield Teff ≈2100–2300 K and 1800–2000 K for the two L-dwarf candidates and <1000 K for the late‑T object, with distances around 2 kpc; adding an extinction term notably improves Y/J/H residuals, especially for o006_s35616. NIRCam color–color planes place the cool T dwarf within the little red dot locus while the hotter L dwarfs sit among high‑z galaxy selections, implying ≈0.1% brown‑dwarf contamination in deep extragalactic surveys dominated by L dwarfs. The work pins down how specific substellar SED shapes infiltrate LRD/high‑z samples and shows that low‑resolution prism spectra efficiently weed them out.
Key figures to inspect
- Figure 1: Compare observed PRISM spectra to best‑fit models for each object to see the H2O/CH4‑shaped V‑profile (∼1–2.4 μm) and the percent residuals; use the RGB cutouts to confirm point‑source morphology that would masquerade as compact high‑z systems.
- Figure 2: For o006_s35616, inspect the with‑vs‑without extinction fits to see how adding AV suppresses the pronounced Y/J/H residuals and brings the model into agreement—evidence that modest line‑of‑sight reddening affects the apparent L‑dwarf SED.
- Figure 3: Read the placement of o005_s41280, o006_s00089, and o006_s35616 on NIRCam color–color and color–magnitude planes relative to RUBIES sources and LRDs to understand why the T dwarf overlaps the LRD locus while L dwarfs intrude on high‑z galaxy selections, quantifying the contamination pathway.