THE HETDEX PILOT SURVEY. I. SURVEY DESIGN, PERFORMANCE, AND CATALOG OF EMISSION-LINE GALAXIES

We present a catalog of emission-line galaxies selected solely by their emission-line fluxes using awide-field integral field spectrograph. This work is partially motivated as a pilot survey for the upcoming Hobby-Eberly Telescope Dark Energy Experiment. We describe the observations, reductions, detections, redshift classifications, line fluxes, and counterpart information for 397 emission-line galaxies detected over 169 square' with a 3500-5800 angstrom bandpass under 5 angstrom full-width-half-maximum (FWHM) spectral resolution. The survey's best sensitivity for unresolved objects under photometric conditions is between 4 and 20 x 10(-17) erg s(-1) cm(-2) depending on the wavelength, and Ly alpha luminosities between 3 x 10(42) and 6 x 10(42) erg s(-1) are detectable. This survey method complements narrowband and color-selection techniques in the search of high-redshift galaxies with its different selection properties and large volume probed. The four survey fields within the COSMOS, GOODS-N, MUNICS, and XMM-LSS areas are rich with existing, complementary data. We find 105 galaxies via their high-redshift Lya emission at 1.9 < z < 3.8, and the majority of the remainder objects are low-redshift [O II] 3727 emitters at z < 0.56. The classification between low-and high-redshift objects depends on rest-frame equivalent width (EW), as well as other indicators, where available. Based on matches to X-ray catalogs, the active galactic nuclei fraction among the Ly alpha emitters is 6%. We also analyze the survey's completeness and contamination properties through simulations. We find five high-z, highly significant, resolved objects with FWHM sizes >44 square '' which appear to be extended Ly alpha nebulae. We also find three high-z objects with rest-frame Ly alpha EW above the level believed to be achievable with normal star formation, EW0 > 240 angstrom. Future papers will investigate the physical properties of this sample.