The Internal Ultraviolet–Optical Color Dispersion: Quantifying the MorphologicalK‐Correction

We present a quantitative measure of the internal color dispersion withingalaxies, which quantifies differences in morphology as a function ofwavelength. We apply this statistic to a local galaxy sample with archivalimages at 1500 and 2500 Angstroms from the Ultraviolet Imaging Telescope, andground-based B-band observations to investigate how the color dispersionrelates to global galaxy properties. The intenal color dispersion generallycorrelates with transformations in galaxy morphology as a function ofwavelength, i.e., it quantifies the morphological K-correction. Mid-type spiralgalaxies exhibit the highest dispersion in their internal colors, which stemsfrom differences in the bulge, disk, and spiral-arm components. Irregulars andlate-type spirals show moderate internal color dispersion, which implies thatyoung stars generally dominate the colors. Ellipticals, lenticulars, andearly-type spirals generally have low or negligible internal color dispersion,which indicates that the stars contributing to the UV-to-optical emission havea very homogeneous distribution. We discuss the application of the internalcolor dispersion to high-redshift galaxies in deep, Hubble Space Telescopeimages. By simulating local galaxies at cosmological distances, many of thegalaxies have luminosities that are sufficiently bright at rest--frame opticalwavelengths to be detected within the limits of the currently deepestnear-infrared surveys even with no evolution. Under assumptions that theluminosity and color evolution of the local galaxies conform with the measuredvalues of high-redshift objects, we show that galaxies' intrinsic internalcolor dispersion remains measurable out to z ~ 3.