The Muenster redshift project: Improved methods for automated galaxy redshift measurements from very low-dispersion objective-prism spectra

The Muenster Redshift Project (MRSP) is a large low-resolution galaxy-redshift survey, where pairs of film copies of direct and very low-dispersion objective-prism Schmidt plates are analysed fully automatically. This communication describes updated methods employed for the determination of galaxy redshifts z. For calibration, 1183 galaxies with z less than or equal to 0.3 and r(F) less than or equal to 18.5 (b(J) less than or equal to 19.5) are used. The spectra have the linear reciprocal dispersion 245 nm mm(-1) at H gamma. The random errors range between sigma(z) = 0.011 (best subsamples) and 0.031 (total sample). For the total sample the redshift errors depend on redshift, magnitude, morphological type and galactic latitude. The corresponding corrections can be obtained from the measured error distributions given in this paper. The best subsamples are not contaminated by galaxies with large systematic errors, and can be used for cosmological investigations, taking into account only the magnitude-dependent effects. It should be noted that galaxy redshifts obtained with low-resolution spectra cannot be used individually. However, the large number of redshifts and the large survey volumes permit the determination of statistical quantities with high significance.