Galaxy Bimodality

The figure below shows the color-magnitude distribution of galaxies from the Sloan Digital Sky Survey at z<0.1. The black solid and dashed contours represent the number density of galaxies: logarithmically spaced with four contours per factor of ten. The distribution is called bimodal because if a color histogram is plotted there are two peaks corresponding to a red sequence (generally early types) and a blue sequence (late types). The red and blue shaded regions show the mean and dispersion (plus/minus 1 sigma) of the red and blue sequences based on the fitting described by Baldry et al. (2004). The dotted lines represent galaxies of similar stellar masses using the mass-to-light ratios of the MPA Garching group (Kauffmann et al. 2003).

The figure is a modified version of Figure 2 from Baldry et al. (2004).

bimodal color-magnitude distribution for galaxies

Link: download PS figure.

Ivan Baldry, written 2006 February 13.