Mapping the column density and dust temperature structure of IRDCs with Herschel

TL;DR

This study uses Herschel data to create detailed maps of dust temperature and column density in IRDCs, revealing significant internal temperature variations and potential prestellar cores, which are crucial for understanding early star formation.

Contribution

Developed a pixel-by-pixel SED fitting method to accurately map temperature and density variations in IRDCs using Herschel data, advancing the analysis of star-forming regions.

Findings

Dust temperature decreases from 20-30 K to 8-15 K within IRDCs.

Temperature gradients influence cloud fragmentation.

Identified candidate massive prestellar cores with high column densities.

Abstract

Infrared dark clouds (IRDCs) are cold and dense reservoirs of gas potentially available to form stars. Many of these clouds are likely to be pristine structures representing the initial conditions for star formation. The study presented here aims to construct and analyze accurate column density and dust temperature maps of IRDCs by using the first Herschel data from the Hi-GAL galactic plane survey. These fundamental quantities, are essential for understanding processes such as fragmentation in the early stages of the formation of stars in molecular clouds. We have developed a simple pixel-by-pixel SED fitting method, which accounts for the background emission. By fitting a grey-body function at each position, we recover the spatial variations in both the dust column density and temperature within the IRDCs. This method is applied to a sample of 22 IRDCs exhibiting a range of angular sizes and peak column densities. Our analysis shows that the dust temperature decreases significantly within IRDCs, from background temperatures of 20-30 K to minimum temperatures of 8-15 K within the clouds, showing that dense molecular clouds are not isothermal. Temperature gradients have most likely an important impact on the fragmentation of IRDCs. Local temperature minima are strongly correlated with column density peaks, which in a few cases reach NH2 = 1 x 10^{23} cm^{-2}, identifying these clouds as candidate massive prestellar cores. Applying this technique to the full Hi-GAL data set will provide important constraints on the fragmentation and thermal properties of IRDCs, and help identify hundreds of massive prestellar core candidates.