2009ApJ...693.1045C

We study internal extinction of late-type galaxies in the Sloan Digital Sky Survey. We find that the degree of internal extinction depends on both the concentration index c and K_s-band absolute magnitude M_K. We give simple fitting functions for internal extinction. In particular, we present analytic formulae giving the extinction-corrected magnitudes from the observed optical parameters. For example, the extinction-corrected r-band absolute magnitude can be obtained by, where Δ = 0.236{1.35(c - 2.48)² - 1.14} log(a/b), c = R₉₀/R₅₀ is the the concentration index, and a/b is the isophotal axis ratio of the 25 mag arcsec^–2 isophote in the i band. The 1σ error in M_r,0 is 0.21 log(a/b). Late-type galaxies with very different inclinations are found to trace almost the same sequence in the (u - r)-M_r diagram when our prescriptions for extinction correction are applied. We also find that (u - r) color can be a third independent parameter that determines the degree of internal extinction.