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We present Keck/NIRSPEC spectroscopic observations of three Lyman alphaemitting galaxies (LAEs) at z ~ 2.3 discovered with the HETDEX pilot survey. Wedetect Halpha, [OIII], and Hbeta emission from two galaxies at z = 2.29 and2.49, designated HPS194 and HPS256, respectively, representing the firstdetection of multiple rest-frame optical emission lines in galaxies athigh-redshift selected on the basis of their Lyman alpha emission. Theredshifts of the Lyman alpha emission from these galaxies are offset redward ofthe systemic redshifts by Delta_v = 162 +/- 37 (photometric) +/- 42(systematic) km/s for HPS194, and Delta_v = 36 +/- 35 +/- 18 km/s for HPS256.An interpretation for HPS194 is that a large-scale outflow may be occurring inits interstellar medium. The emission line ratios imply that neither LAE hostsan active galactic nucleus. Using the upper limits on the [NII] emission weplace meaningful constraints on the gas-phase metallicities in these two LAEsof Z < 0.17 and < 0.28 Zsol (1 sigma). Measuring the stellar masses of theseobjects via spectral energy distribution (SED) fitting (~ 10^10 and 6 x 10^8Msol, respectively), we study the nature of LAEs in a mass-metallicity plane.At least one of these two LAEs appears to be more metal poor thancontinuum-selected star-forming galaxies at the same redshift and stellar mass,implying that objects exhibiting Lyman alpha emission may be systematicallyless chemically enriched than the general galaxy population. We use the SEDs ofthese two galaxies to show that neglecting the emission lines when fittingstellar population models to the observed photometry can result inoverestimates of the population age by orders of magnitude, and the stellarmass by a factor of ~ 2. This effect is particularly important at z > 7, wheresimilarly strong emission lines may masquerade in the photometry as a 4000 Abreak (abridged).

The HETDEX Pilot Survey III: The Low Metallicities of High-Redshift Lyman Alpha Galaxies