The HETDEX Survey: The Ly$\alpha$ Escape Fraction from 3D-HST Emission
  Line Galaxies at $z \sim 2$
  We measure the Ly$\alpha$ escape fraction of 935 [OIII]-emitting galaxies
between $1.9 < z < 2.35$ by comparing stacked spectra from the Hubble Space
Telescope/WFC3's near-IR grism to corresponding stacks from the Hobby Eberly
Telescope Dark Energy Experiment's Internal Data Release 2. By measuring the
stacks' H$\beta$ to Ly$\alpha$ ratios, we determine the Ly$\alpha$ escape
fraction as a function of stellar mass, star formation rate, internal
reddening, size, and [OIII]/H$\beta$ ratio. We show that the escape fraction of
Ly$\alpha$ correlates with a number of parameters, such as galaxy size, star
formation rate, and nebular excitation. However, we also demonstrate that most
of these relations are indirect, and the primary variables that control the
escape of Ly$\alpha$ are likely stellar mass and internal extinction. Overall,
the escape of Ly$\alpha$ declines from $\gtrsim 18\%$ in galaxies with $\log
M/M_{\odot} \lesssim 9$ to $\lesssim 1\%$ for systems with $\log M/M_{\odot}
\gtrsim 10$, with the sample's mean escape fraction being
$6.0^{+0.6\%}_{-0.5\%}$.
