Cloud Structure of Three Galactic Infrared Dark Star-forming Regions from Combining Ground- and Space-based Bolometric Observations

Abstract

We have modified the iterative procedure introduced by Lin et al., to systematically combine the submillimeter images taken from ground-based (e.g., CSO, JCMT, APEX) and space (e.g., Herschel, Planck) telescopes. We applied the updated procedure to observations of three well-studied Infrared Dark Clouds (IRDCs): G11.11−0.12, G14.225−0.506, and G28.34+0.06, and then performed single-component, modified blackbody fits to each pixel to derive ∼10″ resolution dust temperature and column density maps. The derived column density maps show that these three IRDCs exhibit complex filamentary structures embedded with rich clumps/cores. We compared the column density probability distribution functions (N-PDFs) and two-point correlation (2PT) functions of the column density field between these IRDCs with several OB-cluster-forming regions. Based on the observed correlation between the luminosity-to-mass ratio and the power-law index of the N-PDF, and complementary hydrodynamical simulations for a 10 4  M molecular cloud, we hypothesize that cloud evolution can be better characterized by the evolution of the (column) density distribution function and the relative power of dense structures as a function of spatial scales, rather than merely based on the presence of star-forming activity. An important component of our approach is to provide a model-independent quantification of cloud evolution. Based on the small analyzed sample, we propose four evolutionary stages, namely,cloud integration, stellar assembly, cloud pre-dispersal, and dispersed cloud. The initial cloud integration stage and the final dispersed cloud stage may be distinguished from the two intermediate stages by a steeper than −4 power-law index of the N-PDF. The cloud integration stage and the subsequent stellar assembly stage are further distinguished from each other by the larger luminosity-to-mass ratio (>40   L M ) of the latter. A future large survey of molecular clouds with high angular resolution may establish more precise evolutionary tracks in the parameter space of N-PDF, 2PT function, and luminosity-to-mass ratio.

The TOP-SCOPE Survey of Planck Galactic Cold Clumps: Survey Overview and Results of an Exemplar Source, PGCC G26.53+0.17

“…We tried to fit the tail with a power law for the N-PDF of G26. Although the power-law fit is poor, its slope (−3.9) is comparable to those of IRDCs G28.34+0.06 (−3.9) and G14.225-0.506 (−4.1) but smaller than those of protoclusters (Lin et al 2016(Lin et al , 2017, indicating that G26 is still at a very young evolutionary stage and is not greatly affected by star formation activities as in high-mass protoclusters.…”

“…We combined the Planck 353 GHz image with the SCUBA-2 850 μm images in the R2 and R4 reductions following the same procedure as in Lin et al (2016Lin et al ( , 2017. In principle, the data combination was performed in the Fourier domain, yielding high-resolution (14″) combined data that have little or no loss of extended structure (Lin et al 2016(Lin et al , 2017.…”

“…In principle, the data combination was performed in the Fourier domain, yielding high-resolution (14″) combined data that have little or no loss of extended structure (Lin et al 2016(Lin et al , 2017. The combined images are shown in Figure 9(a).…”

“…To quantify the dense gas distributions systematically, we perform analyses of the column density probability distribution functions (N-PDF) following Lin et al (2016Lin et al ( , 2017. The natural logarithm of the ratio of column density and mean column density…”

“…The N-PDF in molecular clouds is usually found to consist of a lognormal like part at low column density and a power-law-like part at high column density (Klessen 2000; Kritsuk et al 2011;Schneider et al 2012Schneider et al , 2015Federrath & Klessen 2013;Lin et al 2016Lin et al , 2017. The N-PDF power-law tail is usually linked to the effects of gravity (Klessen 2000;Kritsuk et al 2011;Federrath & Klessen 2013;Lin et al 2016Lin et al , 2017. We tried to fit the tail with a power law for the N-PDF of G26.…”