Internal Extinction in the SDSS Late-Type Galaxies

TL;DR

This study models internal extinction in SDSS late-type galaxies, providing analytic formulas to correct observed magnitudes and revealing that galaxy inclination and color influence extinction.

Contribution

It introduces new fitting functions and analytic formulas for internal extinction correction based on galaxy parameters, improving accuracy in magnitude and color measurements.

Findings

Extinction depends on concentration index and absolute magnitude.

Analytic formulas enable precise extinction correction from optical parameters.

Galaxies with different inclinations follow similar extinction-corrected sequences.

Abstract

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 M_{r,0}=-20.77 +(-1+\sqrt{1+4\Delta (M_{r,obs}+20.77+4.93\Delta)})/2\Delta, where \Delta = 0.236\{1.35(c-2.48)^2-1.14\}\log(a/b), c=R_{90}/R_{50} 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 1\sigma error in M_{r,0} is 0.21{\rm log}(a/b). The 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.