The effect of dust extinction on the observed properties of galaxies in the near-infrared

Abstract

Galaxies behind the Milky Way suffer size reduction and dimming due to their obscuration by dust in the disk of our Galaxy. The degree of obscuration is wavelength dependent. It decreases towards longer wavelengths. Compared to the optical, the Near InfraRed (NIR) $K_s$ band extinction is only $\approx10%$ that of the $B$ band. This makes NIR surveys well suited for galaxy surveys close to the Galactic Plane where extinction is severe. While Galactic obscuration is less prominent in the NIR it is not negligible. In this paper we derive empirical relations to correct isophotal radii and magnitudes of galaxies observed in the NIR for foreground absorption. We simulate extinction in the $J$, $H$ and $K_s$ bands on 64 (unobscured) galaxies from the 2MASS Large Galaxy Atlas \citep{jarrett}. We propose two methods for the extinction correction, the first is optimized to provide the most accurate correction and the second provides a convenient statistical correction that works adequately in lower extinction regions. The optimized correction utilizes the galaxy surface brightness, either the disk central surface brightness, $\mu_0$, or the combined disk plus bulge central surface brightness, elliptical and disk/spiral Hubble types. A detailed comparison between the different methods and their accuracy is provided.