A search for small-scale clumpiness in dense cores of molecular clouds

Abstract

We have analyzed HCN(1-0) and CS(2-1) line profiles obtained with high signal-to-noise ratios toward distinct positions in three selected objects in order to search for small-scale structure in molecular cloud cores associated with regions of high-mass star formation. In some cases, ripples were detected in the line profiles, which could be due to the presence of a large number of unresolved small clumps in the telescope beam. The number of clumps for regions with linear scales of ∼0.2–0.5 pc is determined using an analytical model and detailed calculations for a clumpy cloud model; this number varies in the range: ∼2 × 104–3 × 105, depending on the source. The clump densities range from ∼3 × 105–106 cm−3, and the sizes and volume filling factors of the clumps are ∼(1–3) × 10−3 pc and ∼0.03–0.12. The clumps are surrounded by inter-clump gas with densities not lower than ∼(2–7) × 104 cm−3. The internal thermal energy of the gas in the model clumps is much higher than their gravitational energy. Their mean lifetimes can depend on the inter-clump collisional rates, and vary in the range ∼104–105 yr. These structures are probably connected with density fluctuations due to turbulence in high-mass star-forming regions.