Mapping dust column density in dark clouds by using NIR scattered light : Case of the Lupus 3 dark cloud

TL;DR

This paper introduces a novel method for mapping dust column density in dark clouds using near-infrared scattered light, calibrated with background star color excess, enabling detailed maps even in high-density regions.

Contribution

The study presents a new empirical approach combining NIR scattered light and background star colors to map dust density, extending the dynamic range beyond previous methods.

Findings

Mapped dust column density with a dynamic range up to Av=50 mag

Established empirical relations between surface brightness and dust density

First to calibrate using background star color excess for this purpose

Abstract

We present a method of mapping dust column density in dark clouds by using near-infrared scattered light. Our observations of the Lupus 3 dark cloud indicate that there is a well defined relation between (1) the H-Ks color of an individual star behind the cloud, i.e., dust column density, and (2) the surface brightness of scattered light toward the star in each of the J, H, and Ks bands. In the relation, the surface brightnesses increase at low H-Ks colors, then saturate and decrease with increasing H-Ks. Using a simple one-dimensional radiation transfer model, we derive empirical equations which plausibly represent the observed relationship between the surface brightness and the dust column density. By using the empirical equations, we estimate dust column density of the cloud for any directions toward which even no background stars are seen. We obtain a dust column density map with a pixel scale of 2.3 x 2.3 arcsec^2 and a large dynamic range up to Av = 50 mag. Compared to the previous studies by Juvela et al., this study is the first to use color excess of the background stars for calibration of the empirical relationship and to apply the empirical relationship beyond the point where surface brightness starts to decrease with increasing column density.