.To avoid being dominated by a small number of large structures, the survey covers four widely separated regions, called patches, on the sky. The patches are distributed so that two regions can be observed at any time of the year. Each patch is a mosaic of 20 MOS fields, covering ~1400 sq arcmin. The total area of the survey is ~1.5 sq degrees. Each spectroscopically defined MOS field is ~9´×8´, with about 15" overlapping area with the adjacent fields. The field layout, in a L shape with a central block, is shown in Figure 11. The maximum dimensions of the patches span ~80´ NS, and 63´ EW.
We utilize the observational technique developed for the CNOC1 Cluster Redshift Survey (Yee, Ellingson, & Carlberg 1996; hereafter, YEC). Here, we describe briefly the procedure and some improvements. A number of CCD's have been used for this project, but the majority of the data are obtained using the STIS CCD with superior blue response, but a larger 21µ pixel size. Here, for brevity, we describe primarily the observational parameters for runs using the higher QE STIS CCD.
detection magnitudes for R and B of 24.0 and 24.6, respectively. The photometry is reduced and multicolor catalogs produced in real time at the telescope. Using the catalogs, multislit masks are designed using a computer program which allows one to prioritize the sample in various ways and optimize the number of slit placements. The slits have a width of 1.3" and a minimum length of 11". The masks, cut using LAMA, are available for the spectroscopic observation within as little as 3 hours after the direct imaging observation. The primary spectroscopic sample is the union set of galaxies with R < 21.5 or B < 22.5. This allows us to construct unbiased R and B samples from the redshift catalogs.
Using the more efficient CCD and including overhead, the total time required for the 5 colors and 2 spectroscopic masks per MOS field is about 3.5 hrs, yielding typically 80 to 90 redshifts. Thus, the complete survey of 80 fields requires about 27 clear nights, providing about 6500 redshifts with a mean z of 0.35. At the intended survey spectroscopic limit of R = 21.5, the cumulative sampling rate for the redshift sample is about 0.50 of the photometric sample, while the differential completeness is about 0.25.
Catalog Creation
The data reduction procedure follows basically that outlined in YEC for the CNOC1 survey. Velocities are determined using cross-correlation. With 5 photometric colors we are also able to verify the redshift assignment. Survey Status
The survey is presently (Dec 97) 80% complete, and will be completed by the spring of 1998. The current reduced sample contains ~4000 redshifts, with an additional ~1000 redshifts to be obtained from the data currently being reduced. From the redundant observations the typical rms uncertainty of the velocity determination is about 75 km s-1 in the rest frame.
Figure 14 shows some preliminary LFs obtained from a subsample of 2075 galaxies (from two patches) with R < 21.2. The galaxies are divided into early, intermediate, and late types based on B-R colors. Note the clear difference in the LFs for galaxies with different colors. The CNOC2 sample is about an order of magnitude larger than any other redshift surveys in this redshift range (e.g., CFRS: Lilly et al. 1995; Autofib: Ellis et al. 1996). This large sample size, in combination with extensive UBgRI photometry, will permit precise measurements of the LF and its evolution with redshift for different galaxy populations.
Currently, various projects are being carried out using this large data base. We will be able to determine the galaxy correlation function in redshift and morphological bins, estimate the evolution of the pairwise velocity distribution, and measure the bias of galaxy clustering relative to mass clustering. The data are also being used to create a complete catalog of groups and pairs of galaxies, from which we can study the dynamics and evolution of galaxy groups and the redshift dependence of the merger rate. Line index measurements and principal component analysis of the spectra will be carried out, allowing us to conduct a detailed investigation of the star formation history of the galaxies. In addition, we will also derive quantitative morphological parameters of the galaxies, allowing us to examine the relationship between morphology, environment, and galaxy evolution. We will be able to obtain well-calibrated photometric redshifts for about 20,000 galaxies down to R ~ 22.0, which will further improve our studies of galaxy clustering and populations, and also extend the results to higher redshift.
References:
Ellis, R.S., et al. 1996, MNRAS, 280, 235
