The First JWST Spectral Energy Distribution of a Y Dwarf

We present the first JWST spectral energy distribution of a Y dwarf. This spectral energy distribution of the Y0 dwarf WISE J035934.06-540154.6 consists of low-resolution (lambda/Delta lambda similar to 100) spectroscopy from 1-12 mu m and three photometric points at 15, 18, and 21 mu m. The spectrum exhibits numerous fundamental, overtone, and combination rotational-vibrational bands of H2O, CH4, CO, CO2, and NH3, including the previously unidentified.3 band of NH3 at 3 mu m. Using a Rayleigh-Jeans tail to account for the flux emerging at wavelengths greater than 21 mu m, we measure a bolometric luminosity of 1.523 +/- 0.090 x 10(20) W. We determine a semiempirical effective temperature estimate of 467+ (+16)(-18) K using the bolometric luminosity and evolutionary models to estimate a radius. Finally, we compare the spectrum and photometry to a grid of atmospheric models and find reasonably good agreement with a model having T-eff = 450 K, log g = 3.25 [cm s(-2)], and [M/H] = -0.3. However, the low surface gravity implies an extremely low mass of 1 M-Jup and a very young age of 20 Myr, the latter of which is inconsistent with simulations of volume-limited samples of cool brown dwarfs.