Revealing the mass reservoirs surrounding IRDCs with NIR extinction mapping
Joao Alves, Henrik Beuther, Thomas Henning, Frederic Schuller
Infrared dark clouds (IRDCs) are places where conditions suitable for the formation of massive stars are believed to be developing. We present a new, sensitive view towards a sample of 10 IRDC complexes using a near-infrared dust extinction mapping technique. The derived column density maps reach the sensitivity and resolution similar to the Herschel satellite data, providing an independent measurements of mass distribution at low- to intermediate column densities. The maps reveal tens-of-parsecs scale, low-column density structures surrounding IRDCs, naming the IRDCs as the densest clumps inside (giant) molecular clouds. We compare the extinction maps to molecular gas in the complexes traced by CO emission, and to dense gas traced by mid-infrared extinction and sub-mm dust emission. This comparison shows that the fraction of dense case is typically 5-10 % of the total mass reservoir of the clouds. We discuss how the derived properties compare to the nearby molecular clouds.