The Bimodal Galaxy Color Distribution: Dependence on Luminosity and Environment

We analyse the u-r color distribution of 24346 galaxies with Mr<=-18 andz<0.08, drawn from the Sloan Digital Sky Survey first data release, as afunction of luminosity and environment. The color distribution is well fit withtwo Gaussian distributions, which we use to divide the sample into a blue andred population. At fixed luminosity, the mean color of the blue (red)distribution is nearly independent of environment, with a weakly significant(~3sigma) detection of a trend for colors to become redder by 0.1-0.14(0.03-0.06) mag with a factor ~100 increase in local density, as characterisedby the surface density of galaxies within a +/-1000 km/s redshift slice. Incontrast, at fixed luminosity the fraction of galaxies in the red distributionis a strong function of local density, increasing from ~10-30 per cent of thepopulation in the lowest density environments, to ~70 per cent at the highestdensities. The strength of this trend is similar for both the brightest(-23

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