Using the Galactic Dynamics of M7 Dwarfs to Infer the Evolution of Their Magnetic Activity

We present a spectroscopic study and dynamical analysis of ∼2600 M7 dwarfs. We confirm our previous finding that the fraction of magnetically active stars decreases with vertical distance from the Galactic plane. We also show that the mean luminosity of the Hα emission has a small but statistically significant decrease with distance. Using space motions for ∼1300 stars and a simple one-dimensional dynamical simulation, we demonstrate that the drop in the activity fraction of M7 dwarfs can be explained by thin disk dynamical heating and a rapid decrease of magnetic activity at a mean stellar age of ∼6-7 Gyr.