An Optical Multicolor System for Measuring Galaxy Redshifts and Spectral Types

A method of obtaining approximate redshifts and spectral types of galaxiesusing a photometric system of six broad-bandpass filters is developed. Thetechnique utilizes a smallest maximum difference approach rather than aleast-squares approach, and does not consider a galaxy's apparent magnitude inthe determination of its redshift. In an evalution of its accuracy using twodistinct galaxy samples, the photometric redshifts are found to have a rootmean square deviation of $\pm$0.05 from spectroscopically determined redshifts.Possible systematic errors of the method are investigated, including theeffects of post-starburst (``E+A'') galaxies and attempts to measure redshiftswith incomplete color information. Applications of the technique are discussed.Comment: Accepted to AJ; 22 pages including figure