INCLINATION-DEPENDENT EXTINCTION EFFECTS IN DISK GALAXIES IN THE SLOAN DIGITAL SKY SURVEY

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 less than or similar to -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 Delta M-r = 1.27(log(q))(2), rather than the Delta M alpha log q law that is frequently assumed. When the absolute magnitudes of bright exponential galaxies are corrected to their face-on'' value, M-r(f) M-r - Delta M-r, the average u - r color is linearly dependent on M-r(f) r for a given value of q; the value of d(u r)/dM(r)(f) r ranges from similar to 0.10 for nearly face-on galaxies (q > 0: 9) to similar to 0.26 for nearly edge-on galaxies (q < 0.3). When the dimming law Delta M-r alpha (log q)(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 gamma approximate to 0.22 and median disk ellipticity is an element of approximate to 0.08.