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J. Alves (European Southern Observatory), M. Lombardi (University of Bonn)
We generalize the technique of Lada et al. (1994) to map dust column density through a molecular cloud (NICE) to an optimized multi-band technique (NICER) that can be applied to any multi-band survey of molecular clouds. We present a first application to a ~ 625 deg2 subset of the Two Micron All Sky Survey (2MASS) data and show that when compared to NICE, the optimized NICER technique (i) achieves the same extinction peak values, (ii) improves the noise variance of the map by a factor of 2 and (iii) is able to reach 3 sigma dust extinction measurements as low as AV ~ 0.5 magnitudes, better than or equivalent to classical optical star count techniques and below the threshold column density for the formation of CO, the brightest H2 tracer in radio-spectroscopy techniques. The application of the NICER techniques to near-infrared data obtained with a 8 meter-class telescope with a state-of-the-art NIR camera, such as the VLT-ISAAC combination, will be able to achieve dynamic ranges from below 1021 protons cm-2 to over 1023 protons cm-2 (AV in the range [0.3, 60] mag) and spatial resolutions <10", making use of a single and straightforward column density tracer, extinction by interstellar dust.
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