Early results from GLASS-JWST. XIII. A faint, distant, and cold brown dwarf (2207.14802v2)

Abstract: We present the serendipitous discovery of a late T-type brown dwarf candidate in JWST NIRCam observations of the Early Release Science Abell 2744 parallel field. The discovery was enabled by the sensitivity of JWST at 4~$\mu$m wavelengths and the panchromatic 0.9--4.5~$\mu$m coverage of the spectral energy distribution. The unresolved point source has magnitudes F115W = 27.95$\pm$0.15 and F444W = 25.84$\pm$0.01 (AB), and its F115W$-$F444W and F356W$-$F444W colors match those expected for other, known T dwarfs. We can exclude it as a reddened background star, high redshift quasar, or very high redshift galaxy. Comparison with stellar atmospheric models indicates a temperature of $T_{eff}$ $\approx$ 600~K and surface gravity $\log{g}$ $\approx$ 5, implying a mass of 0.03~M$_{\odot}$ and age of 5~Gyr. We estimate the distance of this candidate to be 570--720~pc in a direction perpendicular to the Galactic plane, making it a likely thick disk or halo brown dwarf. These observations underscore the power of JWST to probe the very low-mass end of the substellar mass function in the Galactic thick disk and halo.

• The paper demonstrates the discovery of a distant brown dwarf in the JWST ERS Abell 2744 field via deep infrared imaging.
• The paper determines GLASS-JWST-BD1’s physical properties, with an effective temperature of ~650 K and mass ~0.03 M☉, consistent with a late T-type classification.
• The paper excludes alternate explanations such as reddened stars or distant galaxies, indicating the object likely belongs to the Galactic thick disk or halo.

Discovery of a Remote Brown Dwarf in the JWST ERS Abell 2744 Field

The paper entitled "Early results from GLASS-JWST. XIII. A faint, distant, and cold brown dwarf" by Nonino et al. describes the serendipitous discovery of a brown dwarf candidate using data from the James Webb Space Telescope (JWST) in the Abell 2744 parallel field. This discovery was facilitated by the sensitivity of JWST's instruments in capturing data at wavelengths around 4 μm, along with the comprehensive panchromatic coverage from 0.9 to 4.5 μm, allowing the detailed observation of such objects, which predominantly emit in the infrared spectrum.

Brown dwarfs are substellar objects that possess masses below the threshold for hydrogen fusion (i.e., < 0.07 M☉) and emit primarily in the infrared due to their low effective temperatures. The brown dwarf candidate identified by Nonino et al., designated GLASS-JWST-BD1, was observed with significant infrared magnitudes (F115W = 27.95 and F444W = 25.84 in the AB magnitude system), and its color indices correspond to those typical of late T-type spectral classifications. Detailed spectral energy distribution (SED) analysis using atmospheric models indicates an effective temperature of approximately 650 K, a surface gravity of log(g) ≈ 5.25, and an implied mass around 0.03 M☉.

The paper presents a meticulous examination of the candidate's properties, excluding alternative explanations such as it being a reddened star, a high-redshift quasar, or a distant galaxy based on its color and magnitude parameters. The distance to GLASS-JWST-BD1 is estimated to be between 570 and 720 parsecs, suggesting its affiliation with the Galactic thick disk or halo populations, rather than the more prevalent thin disk brown dwarfs near the solar neighborhood.

The research illuminates JWST's capacity to extend the observational reach into the low-mass range of the substellar domain, offering insights into population statistics and physical diversity of brown dwarfs, particularly in less explored Galactic components like the thick disk and the halo. This capability greatly enhances understanding of star formation processes and the evolutionary pathways of substellar objects.

The theoretical implications of this discovery are extensive. It opens new avenues for probing the metallicity dependence of star formation at low masses, thus informing models of galactic structure and evolution. The observational limits reached by JWST in detecting such objects pave the way for various future studies, potentially focusing on conducting large-scale surveys to refine the density and distribution of thick disk and halo brown dwarfs.

Overall, Nonino et al.'s work emphasizes the unprecedented depth and precision facilitated by JWST, marking a significant advancement in astrophysical observations of substellar objects. Further spectroscopic analysis and potential follow-up with additional JWST data could yield even more refined characterizations of such distant brown dwarfs, enhancing theoretical models and enriching the taxonomy of brown dwarf spectral classes.