Cross-correlation techniques for the determination of galaxy redshifts

It is noted that with the advent of digital linear-response detectors it is possible to obtain accurate and objective redshifts by cross-correlating all or part of the galaxy spectrum with a template galaxy of known redshift. In this way, the problem of identifying and measuring wavelengths for blended features is avoided. The cross-correlation methods presented here were developed for the analysis of low-resolution (approximately 10 A FWHM) spectra obtained with the image-dissector scanner on the 3.9 m Anglo-Australian Telescope in a program to examine the properties of radio sources in rich clusters of galaxies. The calibration procedures required for preparing the raw digital spectra for cross-correlation analysis are enumerated. It is found that these cross-correlation techniques are capable of redshifts accurate to approximately 30 km/sec rms. It is noted that this accuracy is attained with a simple wavelength calibration procedure that does not consume additional observing time.