HETDEX Public Source Catalog 1-Stacking 50,000 Lyman Alpha Emitters

We describe the ensemble properties of the 1.9 < z < 3.5 Lyman alpha emitters (LAEs) found in the HETDEX survey's first public data release, HETDEX Public Source Catalog 1. Stacking the low-resolution (R similar to 800) spectra greatly increases the signal-to-noise ratio (S/N), revealing spectral features otherwise hidden by noise, and we show that the stacked spectrum is representative of an average member of the set. The flux-limited, Ly alpha a S/N restricted stack of 50,000 HETDEX LAEs shows the ensemble biweight average z similar to 2.6 LAE to be a blue (UV continuum slope similar to-2.4 and E(B - V) < 0.1), moderately bright (M-UV similar to-19.7) star-forming galaxy with strong Ly alpha emission (log L-Ly alpha similar to 42.8 and W lambda(Ly alpha) similar to 114 angstrom), and potentially significant leakage of ionizing radiation. The rest-frame UV light is dominated by a young, metal-poor stellar population with an average age of 5-15 Myr and metallicity of 0.2-0.3 Z(circle dot).