A complete galaxy redshift sample - IV. Optical and infrared colour-luminosity relations

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Abstract
We present infrared and optical photometry for a complete sub-sample of 194 galaxies in the Anglo–Australian Redshift Survey. The data are reduced to zero-redshift colours at a fixed aperture size in a self-consistent manner. Infrared and optical-to-infrared colour–luminosity (C–L) relations are analysed both as a function of morphological type and, in conjunction with published data, as a function of environment. We find evidence to support the existence of an infrared C–L relation for all galaxy types. The slope seen for E/S0 galaxies slrengthens the hypothesis that metallicily is the driving factor in the relation for all types at infrared and optical wavelengths. The C–L relations for spirals have a slope that is substantially steeper but the relations do not vary significantly with Hubble type when corrections for bulge contamination are made. The results imply that both bulge and disc material have distinct enrichment histories that depend on luminosity in a simple way irrespective of the host galaxy type. The infrared C–L relation is fairly tight; the intrinsic scatter is small and we cannot yet detect any environmental dependence. The relation for our field E/S0s agrees closely with that seen in both the Virgo and Coma clusters and is consistent with recent estimates of the Local Group motion; there is no evidence for any anomalous population of cool stars in the Virgo cluster galaxies. Although promising as a distance indicator in cluster samples, infrared photometry of high precision is required. The optical–infrared relation for spirals, however, has intrinsic scatter over and above the effects of bulge contamination most likely due to varying amounts of star formation at a fixed luminosity and bulge/disc ratio. An application of our bulge-corrected optical–infrared C–L relation to Bothun‗s sample of nearby cluster spirals produces an intrinsic scatter from cluster to cluster which is apparently three times worse than that seen using the infrared Tully–Fisher relation if a recent solution for the Local Group motion is adopted.

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