Radio Sources in the 2dF Galaxy Redshift Survey. I. Radio source populations¹
Elaine M. Sadler , V.J. McIntyre , C.A. Jackson , R.D. Cannon, PASA, 16 (3), 247.

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The optical data

Our data set comprises the thirty fields observed by the 2dFGRS team in November 1997 and January 1998. Twenty-three of these are in the southern Galactic hemisphere and the other seven in the north. They include a total of 8362 target galaxies brighter than $b_{\rm J}$ magnitude 19.4.

Although each 2dF field covers about 3.14 square degrees, the total effective area covered by the 30 fields is somewhat less than 90 square degrees because there is some overlap between adjacent fields. Also, the fractional completeness of this early sample varies substantially from field to field. In many fields about 30% of the fibres were allocated to targets in a parallel QSO survey; the 2dFGRS uses a flexible tiling algorithm to deal with this and with the intrinsic variations in target density across the sky. When complete, the GRS will yield spectra for around 95% of all galaxies in the input catalogue. The current sample has variable levels of completeness (in terms of the surface distribution of all galaxies brighter than

$b_{\rm J}=19.4$ mag.), though there should be no systematic effects depending on the magnitude, redshift or other properties of the galaxies.

The standard observing pattern for the 2dFGRS is a set of three consecutive 20-minute exposures per field, together with calibration arcs and flat fields. The total exposure time is well-matched to the time required to reconfigure a second set of fibres for the next observation. Up to 380 galaxies can be observed simultaneously, with some 20 fibres allocated to sky. In many fields, however, the total number of galaxies is closer to 250 since a deep QSO survey is being carried out in parallel with the galaxy redshift survey.

Using 300 lines/mm gratings, the 2dFGRS spectra cover the wavelength range 3800Å to 8000Å at a resolution of about 10Å. Most spectra have a signal-to-noise ratio (S/N) of 10 (per 4Å pixel) or better. Reliable redshifts are obtained for up to 95% of the targets in good observing conditions; the survey average is currently about 90% (Folkes et al. 1999). About 5% of the targets are found to be foreground stars; the original selection was for objects which appeared non-stellar in digitised data from UK Schmidt Telescope sky survey photographs, using a conservative criterion to minimise the number of galaxies missed.

Figure 1 shows three spectra from the survey, and gives an idea of the typical quality of 2dFGRS spectra for galaxies with redshifts around z=0.15 and $b_{\rm J}$ magnitudes in the range 17.6-18.9.

**Figure 1:** Spectra of three 2dFGRS radio sources, showing the three main spectral classes: (top) A star-forming galaxy, TGN239Z082, with strong Balmer emission lines of H $\alpha$ $\lambda 6563$ and H $\beta$ $\lambda 4861$ , as well as weaker emission lines of [SII] $\lambda$ 6716,6731, [NII] $\lambda$ 6583, [OIII] $\lambda$ 4959,5007 and [OII] $\lambda$ 3727; (middle) an emission-line AGN, TGS234Z066, with a Seyfert-like spectrum which has broad H $\alpha$ emission and [OIII] much stronger than H $\beta$ ; (bottom) A radio-galaxy, TGS236Z065, with an absorption-line spectrum typical of giant elliptical galaxies.
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Next Section: The radio data
Title/Abstract Page: Radio Sources in the
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Contents Page: Volume 16, Number 3

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The optical data