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

Context. The details of how galaxies have evolved over cosmological times are imprinted in their star formation history, chemical enrichment and morpho-kinematic structure. Parameters behind these, such as effective temperature and metallicity, can be measured by combining photometric techniques with modelling. However, there are uncertainties with this indirect approach 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 both community use and as a test of the methods used for future use on a wider area. The reddening, a measurement of dust extinction, acts as a tracer of the interstellar medium (ISM). Methods. Near-infrared (NIR) photometry of the red clump stars is used to measure reddening as their fixed luminosity and intermediate age make extinction the dominant cause of colour and magnitude variance. The star formation history derived previously from these data is used to produce an intrinsic colour to act as a zero point in converting colour to reddening values E(J - K-s) which are subsequently converted to visual extinction A(V). Results. Presented is a dust map for the 30 Doradus field in both A(V) and E(J - K-s). This map samples a region of 1 degrees x 1.degrees 5, containing similar to 1.5 x 10(5) red clump stars which probe reddening up to A(V) similar or equal to 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 mu m 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 N-H similar or equal to 4 x 10(21) cm(-2) and N-H similar or equal to 6 x 10(21) cm(-2).