2008ApJ...687..976U

We analyze the r-band absolute magnitude and u-r color of low-redshift (z<0.06) galaxies in the Sloan Digital Sky Survey Data Release 6. Galaxies with nearly exponential profiles (Sloan parameter fracDeV<0.1) fall on the blue sequence of the color-magnitude diagram; if, in addition, these exponential galaxies have M_r≲-19, they show a dependence of u-r color on apparent axis ratio q expected for a dusty disk galaxy. We create a subsample of bright exponential galaxies, with typical Hubble types Sbc and Sc; then, by comparing the normalized luminosity functions for galaxies with different values of q, we measure how the high-luminosity cutoff of the luminosity function depends on apparent axis ratio. In this way, we measure a dependence of dimming on apparent axis ratio well fit by the relation ΔM_r=1.27(logq)², rather than the ΔM∝logq law that is frequently assumed. When the absolute magnitudes of bright exponential galaxies are corrected to their ``face-on'' value, M^f_r=M_r-ΔM_r, the average u-r color is linearly dependent on M^f_r for a given value of q; the value of d(u-r)/dM^f_r ranges from ∼0.10 for nearly face-on galaxies (q>0.9) to ∼0.26 for nearly edge-on galaxies (q<0.3). When the dimming law ΔM_r∝(logq)² is used to create an inclination-corrected sample of bright exponential galaxies, their apparent shapes are consistent with a distribution of mildly noncircular disks, with median short-to-long axis ratio γ~0.22 and median disk ellipticity ε~0.08.