Mass reservoirs surrounding massive infrared dark clouds: A view by near-infrared dust extinction

摘要

Context: Infrared Dark Clouds (IRDCs) harbor progenitors of high-mass stars.Little is known of the parental molecular clouds of the IRDCs. Aims: Wedemonstrate the feasibility of the near-infrared (NIR) dust extinction mappingin tracing the parental molecular clouds of IRDCs at the distances of D = 2.5 -8 kpc. Methods: We derive NIR extinction maps for 10 prominent IRDC complexesusing a color-excess mapping technique and NIR data from the UKIDSS/GalacticPlane Survey. We compare the resulting maps to the 13CO emission line data, tothe 8 \mu m dust opacity data, and to the millimeter dust emission data. Wederive distances for the clouds by comparing the observed NIR source densitiesto the Besancon stellar distribution model and compare them to the kinematicdistance estimates. Results: The NIR extinction maps provide a view to the IRDCcomplexes over the dynamical range of Av = 2 - 40 mag, in spatial resolution of30". The NIR extinction data correlate well with the 13CO data and probe asimilar gas component, but also extend to higher column densities. The NIR datareveal a wealth of extended structures surrounding the dense gas traced by the8 \mu m shadowing features and sub-mm dust emission, showing that the cloudscontain typically > 10 times more mass than traced by those tracers. The IRDCcomplexes of our sample contain relatively high amount of high-column densitymaterial, and their cumulative column density distributions resemble activenearby star-forming clouds like Orion rather than less active clouds likeCalifornia. Conclusions: NIR dust extinction data provide a new powerful toolto probe the mass distribution of the parental molecular clouds of IRDCs up tothe distances of D = 8 kpc. This encourages for deeper NIR observations ofIRDCs, because the sensitivity and resolution of the data can be directlyenhanced with dedicated observations.