Abstract

A method of mapping dust column density in dark clouds using near-infrared scattered light is presented. Deep NIR observations have revealed that the Lupus 3 dark cloud appears as a NIR reflection nebula. The observations indicate that there is a well-defined relationship between (1) the H - K_s color of individual stars behind the cloud, i.e., the dust column density, and (2) the surface brightness of scattered light towards the stars in each of the J, H, and K_s bands. Using a simple one-dimensional radiation transfer model, we derived the empirical equations that plausibly represent the observed relationship between the surface brightness and the dust column density. Using the empirical equations, we estimated the dust column density of the cloud for any direction towards which even no background stars are seen. We obtained a dust column density map with a pixel scale of 2.3"X2.3" and a large dynamic range of up to Av = 50 mag.