Understanding star formation in molecular clouds

摘要: Column-density maps of molecular clouds are one the most important observables in context cloud- and star-formation (SF) studies. With Herschel satellite it is now possible to precisely determine column density from dust emission, which best tracer bulk material clouds. However, line-of-sight (LOS) contamination fore- or background can lead overestimating emission clouds, particular for distant This implies values that too high mass, potentially an incorrect physical interpretation probability distribution function (PDF). In this paper, we use observations simulations demonstrate how LOS affects PDF. We apply a first-order approximation (removing constant level) Auriga Maddalena (low-mass star-forming), Carina NGC 3603 (both high-mass SF regions). perfect agreement with simulations, find PDFs become broader, peak shifts lower densities, power-law tail PDF higher densities flattens after correction. All corrected have lognormal part low at Av ~ 2 mag, deviation point (DP) Av(DP) 4-5 densities. Assuming equivalent spherical ρ ∝ r- α, slopes tails correspond αPDF = 1.8, 1.75, 2.5 Auriga, Carina, 3603. These numbers agree within uncertainties α ≈ 1.5,1.8, determined slope γ (with 1-γ) obtained radial profiles (N rγ). While 1.5-2 consistent structure dominated by collapse (local free-fall individual cores clumps global collapse), value > requires process leads additional compression (e.g., expanding ionization fronts). From small sample our study, forming only low-mass stars those also slightly different their average (1.8 × 1021 cm-2 vs. 3.0 cm-2), they display differences overall structure. Massive assemble more gas smaller cloud volumes than ones. both types, transition shape into found same (at mag). Low-mass then distribution, likely supersonic turbulence. At external pressure form tail. The relative importance twoprocesses vary between thus observed structure. Appendices available electronic http://www.aanda.orgHerschel as FITS files CDS via anonymous ftp http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/575/A79