Metal-poor Brown Dwarf Kinematics from JWST NIRSpec Spectroscopy
Abstract Galactic archaeology relies on stellar kinematics and chemical abundances to identify various stellar populations and associations. With JWST, Galactic archaeology of ancient metal-poor brown dwarfs is now possible through high-sensitivity, medium-resolution spectroscopy. We present the first metal-poor brown dwarf radial velocity (RV) survey using JWST/NIRSpec G395H spectra ( λ /Δ λ ∼ 3000) for a sample of 23 LTY dwarfs across a wide range of temperatures and metallicities. We introduce a forward-modeling framework to measure robust RVs for brown dwarfs by focusing on the CO fundamental band at ∼4.5 μ m. By comparing to sources with existing high-resolution RV measurements, we demonstrate that G395H RVs can achieve a systematic uncertainty of 5 km s −1 , sufficient to examine their Galactic space motions. We identify kinematic members of the Milky Way’s thin disk, thick disk, and halo populations in this sample. We also confirm WISE J155349.98+693355.2 as likely associated with the Gaia–Enceladus merger remnant, and 2MASS J05325346+8246465 is likely associated with the Thamnos stream. Our study systematically demonstrates that JWST G395H spectroscopy can provide robust RVs in addition to detailed chemical abundances, necessary for Galactic archaeology studies. Future discoveries and characterization of brown dwarfs associated with Galactic halo substructures and streams will enable a stringent test of stellar/substellar formation and evolutionary models for diverse metallicities.
Authors
- Jacqueline K. Faherty (ORCID: https://orcid.org/0000-0001-6251-0573)
- Michael C. Cushing (ORCID: https://orcid.org/0000-0001-7780-3352)
- Christian Aganze (ORCID: https://orcid.org/0000-0003-2094-9128)
- Nicolas Lodieu (ORCID: https://orcid.org/0000-0002-3612-8968)
- Roman Gerasimov (ORCID: https://orcid.org/0000-0003-0398-639X)
- : (ORCID: https://orcid.org/0000-0001-7896-5791)
- Christopher Theissen (ORCID: https://orcid.org/0000-0002-9807-5435)
- ZengHua Zhang (ORCID: https://orcid.org/0000-0003-3047-607X)
- Chih-Chun Hsu (ORCID: https://orcid.org/0000-0002-5370-7494)
- Adam J. Burgasser (ORCID: https://orcid.org/0000-0002-6523-9536)
- Jonathan Gagné (ORCID: https://orcid.org/0000-0002-2592-9612)
- Jason J. Wang (ORCID: https://orcid.org/0000-0003-0774-6502)
- Stanimir Metchev (ORCID: https://orcid.org/0000-0003-3050-8203)
- Genaro Suárez (ORCID: https://orcid.org/0000-0002-2011-4924)
- Aaron M. Meisner (ORCID: https://orcid.org/0000-0002-1125-7384)
- Eileen C. Gonzales (ORCID: https://orcid.org/0000-0003-4636-6676)
- Adam C. Schneider (ORCID: https://orcid.org/0000-0002-6294-5937)
Institutions
- University of Notre Dame (US)
- Northwestern University (US)
- Western University (CA)
- Harvard University (US)
- Universidad de La Laguna (ES)
- University of California San Diego (US)
- Center for Astrophysics Harvard & Smithsonian (US)
- Instituto de Astrofísica de Canarias (ES)
- NSF NOIRLab (US)
- United States Naval Observatory (US)
- Université de Montréal (CA)
- San Francisco State University (US)
- Nanjing University (CN)
- University of Toledo (US)
- Stanford University (US)
Publication Details
- Journal
- The Astrophysical Journal
- Published
- 2026-10-28
- DOI
- https://doi.org/10.3847/1538-4357/aeac53
- Primary Topic
- Stellar, planetary, and galactic studies
- Type
- article
- Field-Weighted Citation Impact
- 0.00
Funders
- National Aeronautics and Space Administration
- Space Telescope Science Institute
- Ministerio de Ciencia e Innovación
- Agencia Estatal de Investigación