The Sonora Substellar Atmosphere Models. IV. Elf Owl: Atmospheric Mixing and Chemical Disequilibrium with Varying Metallicity and C/O Ratios

Disequilibrium chemistry due to vertical mixing in the atmospheres of many brown dwarfs and giant exoplanets is well-established. Atmosphere models for these objects typically parameterize mixing with the highly uncertain K_ zz diffusion parameter. The role of mixing in altering the abundances of C-N-O-bearing molecules has mostly been explored for solar composition atmospheres. However, atmospheric metallicity and the C/O ratio also impact atmospheric chemistry. Therefore, we present the grid of self-consistent cloud-free 1D radiative-convective equilibrium model atmospheres for JWST observations, which includes a variation of K_ zz across several orders of magnitude and also encompasses sub-solar to super-solar metallicities and C/O ratios. We find that the impact of K_ zz on the T(P) profile and spectra is a strong function of both T_ eff and metallicity. For metal-poor objects K_ zz has large impacts on the atmosphere at significantly higher T_ eff compared to metal-rich atmospheres where the impact of K_ zz is seen to occur at lower T_ eff. We identify significant spectral degeneracies between varying K_ zz and metallicity in multiple wavelength windows, in particular at 3-5 μm. We use the atmospheric grid to fit the observed spectra of a sample of 9 early to late T- type objects from T_ eff=550-1150 K. We find evidence for very inefficient vertical mixing in these objects with inferred K_ zz values lying in the range between ∼ 10^1-10^4 cm^2s^-1. Using self-consistent models, we find that this slow vertical mixing is due to the observations probing mixing in the deep detached radiative zone in these atmospheres.