The VMC survey VII. Reddening map of the 30 Doradus field and the structure of the cold interstellar medium

TL;DR

This study presents a detailed reddening map of the 30 Doradus region in the Large Magellanic Cloud using red clump stars, providing insights into the interstellar medium's structure and validating the method against existing maps.

Contribution

The paper introduces a new reddening map of 30 Doradus based on near-infrared photometry of red clump stars, enhancing understanding of dust distribution and ISM structure.

Findings

Reddening correlates with dust emission at 70 microns.

Transition from atomic to molecular hydrogen occurs at specific column densities.

Red clump stars are more affected by cooler dust than hot star-heated dust.

Abstract

Context: The details of how galaxies have evolved are imprinted in their star formation history, chemical enrichment and morpho-kinematic structure. Parameters behind these can be measured by combining photometric techniques with modelling. However, there are uncertainties from the ambiguity of colour and magnitude and the effects of interstellar reddening. Aims: In this paper we present a detailed reddening map of the central 30 Doradus region of the Large Magellanic Cloud; for community use and to test the methods used. The reddening, a measurement of dust extinction, acts as a tracer of the interstellar medium (ISM). Methods: Near infrared photometry of red clump stars are used to measure reddening as extinction is the main cause of their colour and magnitude variance. The star formation history is used to convert colour to reddening values which are subsequently converted to visual extinction. Results: Presented is a dust map for the 30 Doradus field. This map samples a region of 1x1.5 deg, containing ~1.5x10^5 red clump stars which probe reddening up to AV=6 mag. We compare our map with maps from the literature, including optical extinction maps and radio, mid- and far-infrared maps of atomic hydrogen and dust emission. Through estimation of column density we locate molecular clouds. Conclusions: This new reddening map shows correlation with equivalent maps in the literature, validating the method of red clump star selection. We make our reddening map available for community use. In terms of ISM the red clump stars appear to be more affected by the cooler dust measured by 70 micron emission because there is stronger correlation between increasing emission and extinction due to red clump stars not being located near hot stars that would heat the dust. The transition from atomic hydrogen to molecular hydrogen occurs between densities of NH=4x10^21 to 6x10^21 cm^-2.