Multi-line characterization of whole molecular clouds using stratified random sampling

Abstract

We have developed a new technique to characterize the multi-line emission from molecular clouds using statistical sampling. Our method uses available extinction maps to select a relatively small sample of cloud positions that cover the full range of column densities in the cloud, and that can be observed with only a modest investment of telescope time. Here we present the first results of applying this technique to the Perseus molecular cloud, a nearby star-forming region that contains a population of both isolated and clustered protostars. We have used the IRAM 30m telescope to observe a sample of 100 random positions that cover two orders of magnitude in H2 column density. These positions have been observed over the full 3mm wavelength band together with selected portions of the 2 and 1mm bands. We find that the emission properties of most species are strongly correlated with the column density over the whole cloud, and that they can be reproduced using a relative simple radiative transfer model.