The 2dF Galaxy Redshift Survey: Spectra and redshifts

TL;DR

The paper presents the 2dF Galaxy Redshift Survey (2dFGRS) designed to obtain redshifts for ~250000 galaxies to map the nearby large-scale structure. It describes the 2dF instrument, the target source catalogue, survey design with adaptive tiling, spectroscopic data reduction, redshift estimation, survey masks, and the public database. The main scientific contributions include a measurement of the galaxy power spectrum $P(k)$ on scales up to a few hundred $h^{-1}$ Mpc, a determination of redshift-space distortions via the parameter $\beta=\Omega^{0.6}/b$, and detection of baryon oscillations yielding $\Omega_b/\Omega_m = 0.15 \pm 0.07$ and a shape parameter $\Gamma=\Omega h = 0.20 \pm 0.03$. The dataset also provides robust constraints on luminosity-dependent clustering, spectral-type dependence via the $\eta$ parameter, and comprehensive galaxy luminosity and mass densities, establishing a valuable resource for studies of galaxy formation and large-scale structure.

Abstract

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 database. The 2dFGRS uses the 2dF multi-fibre spectrograph on the Anglo-Australian Telescope, which is capable of observing 400 objects simultaneously over a 2-degree 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 80deg x 15deg around the SGP, and the other in the northern Galactic hemisphere spanning 75deg x 10deg along the celestial equator; in addition, there are 99 fields spread over the southern Galactic cap. The survey covers 2000 sq.deg and has a median depth of z=0.11. Adaptive tiling is used to give a highly uniform sampling rate of 93% over the whole survey region. Redshifts are measured from spectra covering 3600A-8000A at a two-pixel resolution of 9.0A and a median S/N of 13 per pixel. All redshift identifications are visually checked and assigned a quality parameter Q in the range 1-5; Q>=3 redshifts are 98.4% reliable and have an rms uncertainty of 85 km/s. The overall redshift completeness for Q>=3 redshifts is 91.8%, but this varies with magnitude from 99% for the brightest galaxies to 90% for objects at the survey limit. The 2dFGRS database is available on the WWW at http://www.mso.anu.edu.au/2dFGRS

Figures (20)

• Figure 1: The 2dFGRS regions shown in an Aitoff projection of R.A. and Dec., with individual 2dF fields marked as small circles. Also shown are the lines of Galactic latitude $|b|$=0, 30, 45. The numbers of survey galaxies in these regions are: 193 550 in the 643 fields of the 80$\degr$$\times$15$\degr$ SGP strip, 139 144 in the 450 fields of the 75$\degr$$\times$10$\degr$ NGP strip, and 57 019 in the 99 fields scattered around the SGP strip.
• Figure 2: The survey fields in the NGP (left) and SGP (right) on maps of the extinction $A_{b_J}$ derived from Schlegel et al. (1998).
• Figure 3: The distribution of extinction corrections $A_{b_J}$ with Galactic latitude $b$ (dots and left axis) and the fraction of corrections larger than a given value (line and right axis).
• Figure 4: The distribution of the 7% of objects in the sample that are not allocated to fibres (NGP strip at top, SGP strip at bottom).
• Figure 5: The distribution of the unallocated objects within the stacked 2dF fields.