The 6dF Galaxy survey: samples, observational techiques and the first data release

Abstract

The 6dF Galaxy Survey (6dFGS) aims to measure the redshifts of around 150000 galaxies, and the peculiar velocities of a 15000-member subsample, over almost the entire southern sky. When complete, it will be the largest redshift survey of the nearby Universe, reaching out to about z ∼ 0.15, and more than an order of magnitude larger than any peculiar velocity survey to date. The targets are all galaxies brighter than Ktot = 12.75 in the 2MASS Extended Source Catalog (XSC), supplemented by 2MASS and SuperCOSMOS galaxies that complete the sample to limits of (H, J, rF, bJ) = (13.05, 13.75, 15.6, 16.75). Central to the survey is the Six-Degree Field (6dF) multifibre spectrograph, an instrument able to record 150 simultaneous spectra over the 5°.7-field of the UK Schmidt Telescope. An adaptive tiling algorithm has been employed to ensure around 95 per cent fibring completeness over the 17046 deg2 of the southern sky with |b| > 10°. Spectra are obtained in two observations using separate V and R gratings, that together give R ∼ 1000 over at least 4000-7500 Å and signal-to-noise ratio ∼10 per pixel. Redshift measurements are obtained semi-automatically, and are assigned a quality value based on visual inspection. The 6dFGS data base is available at http://www-wfau.roe.ac.uk/6dFGS/, with public data releases occurring after the completion of each third of the survey.