The 2dF Galaxy Redshift Survey: spectra and redshifts

The 2dF Galaxy Redshift Survey (2dFGRS) is designed to measure redshifts for approximately 250000 galaxies. This paper describes the survey design, the spectroscopic observations, the redshift measurements and the survey data base. The 2dFGRS uses the 2dF multifibre spectrograph on the Anglo-Australian Telescope, which is capable of observing 400 objects simultaneously over a 2 degrees diameter field. The source catalogue for the survey is a revised and extended version of the APM galaxy catalogue, and the targets are galaxies with extinction-corrected magnitudes brighter than b(J) = 19.45. The main survey regions are two declination strips, one in the southern Galactic hemisphere spanning 80 degrees x 15 degrees around the SGP, and the other in the northern Galactic hemisphere spanning 75 degrees x 10 degrees along the celestial equator; in addition, there are 99 fields spread over the southern Galactic cap. The survey covers 2000 deg(2) and has a median depth of (z) over bar= 0.11. Adaptive tiling is used to give a highly uniform sampling rate of 93 per cent over the whole survey region. Redshifts are measured from spectra covering 3600-8000 Angstrom at a two-pixel resolution of 9.0 Angstrom and a median S/N of 13 pixel(-1). All redshift identifications are visually checked and assigned a quality parameter Q in the range 1-5; Q greater than or equal to3 redshifts are 98.4 per cent reliable and have an rms uncertainty of 85 km s(-1). The overall redshift completeness for Q greater than or equal to3 redshifts is 91.8 per cent, but this varies with magnitude from 99 per cent for the brightest galaxies to 90 per cent for objects at the survey limit. The 2dFGRS data base is available on the World Wide Web at http://www. mso.anu.edu.au/2dFGRS.