An Optical Multicolor System For Measuring Galaxy Redshifts And Spectral Types

A method of obtaining approximate redshifts and spectral types of galaxies using a photometric system of six broad-bandpass filters is developed. The technique utilizes a smallest maximum difference approach rather than a least-squares approach, and does not consider a galaxy’s apparent magnitude in the determination of its redshift. In an evalution of its accuracy using two distinct galaxy samples, the photometric redshifts are found to have a root mean square deviation of ±0.05 from spectroscopically determined redshifts. Possible systematic errors of the method are investigated, including the effects of post-starburst (“E+A”) galaxies and attempts to measure redshifts with incomplete color information. Applications of the technique are discussed.