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Ultracool dwarfs represent a significant proportion of stars in the MilkyWay,and deep samples of these sources have the potential to constrain theformation history and evolution of low-mass objects in the Galaxy. Untilrecently, spectral samples have been limited to the local volume (d<100 pc).Here, we analyze a sample of 164 spectroscopically-characterized ultracooldwarfs identified by Aganze et al. (2022) in the Hubble Space Telescope WFC3Infrared Spectroscopic Parallel (WISP) Survey and 3D-HST. We model the observedluminosity function using population simulations to place constraints onscaleheights, vertical velocity dispersions and population ages as a functionof spectral type. Our star counts are consistent with a power-law mass functionand constant star formation history for ultracool dwarfs, with verticalscaleheights 249$_{-61}^{+48}$ pc for late M dwarfs, 153$_{-30}^{+56}$ pc for Ldwarfs, and 175$_{-56}^{+149}$ pc for T dwarfs. Using spatial and velocitydispersion relations, these scaleheights correspond to disk population ages of3.6$_{-1.0}^{+0.8}$ for late M dwarfs, 2.1$_{-0.5}^{+0.9}$ Gyr for L dwarfs,and 2.4$_{-0.8}^{+2.4}$ Gyr for T dwarfs, which are consistent with priorsimulations that predict that L-type dwarfs are on average a younger and lessdispersed population. There is an additional 1-2 Gyr systematic uncertainty onthese ages due to variances in age-velocity relations. We use our populationsimulations to predict the UCD yield in the JWST PASSAGES survey, a similar anddeeper survey to WISPS and 3D-HST, and find that it will produce acomparably-sized UCD sample, albeit dominated by thick disk and halo sources.

Beyond the Local Volume. II. Population Scaleheights and Ages of Ultracool Dwarfs in Deep HST/WFC3 Parallel Fields