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We present an atmospheric retrieval analysis of the Y0 brown dwarf WISE J035934. 06-540154. 6 using the low-resolution 0. 96--12 m JWST spectrum presented in Beiler₂023. We obtain volume number mixing ratios of the major gas-phase absorbers (H₂O, CH₄, CO, CO₂, PH₃, and H₂S) that are 3--5 more precise than previous work that used HST spectra. We also find an order-of-magnitude improvement in the precision of the retrieved thermal profile, a direct result of the broad wavelength coverage of the JWST data. We used the retrieved thermal profile and surface gravity to generate a grid of chemical forward models with varying metallicity, (C/O) ₐtm, and strengths of vertical mixing as encapsulated by the eddy diffusion coefficient Kᵦz. Comparison of the retrieved abundances with this grid of models suggests that the deep atmosphere of WISE 0359-54 shows signs of vigorous vertical mixing with Kᵦz=10⁹ cm^2 s^-1. To test the sensitivity of these results to our 5-knot spline thermal profile model, we performed a second retrieval using the Madhusudhan₂009 thermal profile model. While the results of the two retrievals generally agree well, we do find differences between the retrieved values of mass and volume number mixing ratio of H₂S with fractional differences of the median values of -0. 64 and -0. 10, respectively. In addition, the 5-knot thermal profile is consistently warmer at pressure between 1 and 70 bar. Nevertheless, our results underscore the power that the broad-wavelength infrared spectra obtainable with the James Webb Space Telescope have to characterize the atmospheres of cool brown dwarfs.
Kothari et al. (Mon,) studied this question.