Spectroscopic CCD surveys for quasars at large redshift. III. The Palomar Transit Grism Survey catalog

This paper reports the initial results of the Palomar Transit Grism Survey (PTGS). The PTGS was designed to produce a sample of z>2.7 quasars that were identified by well-defined selection criteria. The survey consists of six narrow (≈8.5′ wide) strips of sky; the total effective area is 61.47 sq deg. Low-resolution slitless spectra, covering the wavelength range from 4400 to 7500 Å, were obtained for approximately 600 000 objects. The wavelength- and flux-calibrated spectra were searched for emission lines with an automatic software algorithm. A total to 1655 emission features in the grism data satisfied our signal-to-noise ratio and equivalent width selection criteria; subsequent slit spectroscopy of the candidates confirmed the existence of 1052 lines (928 different objects). Six groups of emission lines were detected in the survey: Lyman α+N V, C IV, C III], Mg II, Hβ+[O III], and Hα+[S II]. More than two-thirds of the candidates are low-redshift (z<0.45) emission-line galaxies; ninety objects are high-redshift quasars (z>2.7) detected via their Lyman α+N V emission lines. The survey contains three previously unknown quasars brighter than 17^th magnitude; all three have redshifts of ≈1.3. In this paper we present the observational properties of the survey, the algorithms used to select the emission-line candidates, and the catalog of emission-line objects.