Statistical properties of bright galaxies in the Sloan Digital Sky Survey photometric system

We investigate the photometric properties of 456 bright galaxies using imaging data recorded during the commissioning phase of the Sloan Digital Sky Survey (SDSS). Morphological classification is carried out by correlating results of several human classifiers. Our purpose is to examine the statistical properties of color indices, scale lengths, and concentration indices as functions of morphology for the SDSS photometric system. We find that u′-g′, g′-r′, and r′-i′ colors of SDSS galaxies match well with those expected from the synthetic calculation of spectroscopic energy distribution of template galaxies and with those transformed from UBVR_CI_C color data of nearby galaxies. The agreement is somewhat poor, however, for the i′-z′ color band, with a discrepancy of 0.1-0.2 mag. With the aid of the relation between surface brightness and radius obtained by Kent in 1985, we estimate the averages of the effective radius of early-type galaxies and the scale length of exponential disks both to be 2.6 kpc for L* galaxies. We find that the half-light radius of galaxies depends slightly on the color bands, consistent with the expected distribution of star-forming regions for late-type galaxies and with the known color gradient for early-type galaxies. We also show that the (inverse) concentration index, defined by the ratio of the half-light Petrosian radius to the 90% light Petrosian radius, correlates tightly with the morphological type; this index allows us to classify galaxies into early (E/SO) and late (spiral and irregular) types, allowing for a 15%-20% contamination from the opposite class compared with eye-classified morphology.