Physical description of turbulent and gravitationally bound structures in molecular clouds in relation to the modeling of the general cloud structure

• Applicant: Professor Ralf Klessen, Ph.D.
• Subject Area: Astrophysics and Astronomy
• Term: since 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 284134682

• Final Report Year: 2019

Final Report Abstract

The results achieved within this Project contribute to several important issues of the modern theory of star formation (SF): • Description of the general structure of molecular clouds (MCs): i) Development of a model that predicts the mass-size relationship in MCs, assuming lognor­mal density distribution and equipartition between the gravitational, turbulent and thermal energy at each scale. It is applicable to regions with low or no SF activity as well for such with SF activity but with nearly lognormal distribution of column density. ii) Development of a statistical model that quantifies a link between the notion of scale and the density distribution in MCs, on the assumption for scale-dependent (in the general case) mass-density relationship. In that way, the latter is intertwined with the scaling relations for mass and mean density and relations between scaling exponents in the 2D and 3D cases are obtained. The model is applicable to MCs with various types of column-density distributions: power law, lognormal or combination of both. • Modelling the mass function of prestellar cores (CMF): A CMF model was proposed in the framework of ii), assuming a power-law density distribution with slope q and adding physical postulates about the cores generated at each scale. It is a power law of slope -1, as expected if the cores are considered as hierarchical objects in a fractal cloud and in general agreement with a number of observational studies. The derived CMF of unstable cores displays slope -1 +x/2, i.e. depending on the density distribution in the natal cloud. The model is applicable to MCs at earlier phases of collapse. • Analysis of the (column-)density distribution in star-forming MCs: A novel approach was proposed to extract and assess power-law (PL) tails, with no assumptions about the rest of the distribution. It is based on a mathematical method which was adapted for handling large numerical and obser­ vational data. Applying the approach to numerical simulations on scales 0.5 and 500 pc, one gets evolution of the (column-)density distribution in agreement with theoretical and numerical studies of SF regions. First tests to Herschel data yield PL tails with slopes consistent with estimates from other methods. • Study of clump-finding algorithms: The mixed (neither hierarchical, nor non-hierarchical) technique Gauss-clumps was used to develop an approach for cross-identification (association) between clumps found in different tracers on maps of Rosette MC. All associated CO clumps and all but a few of their dust counterparts are assessed to be gravitationally bound and their location delineates the massive star-forming filaments and their junctions. Their physical analysis indicates low-density clumps formed through compression by converging flows and still not evolved under the influence of self-gravity.

Publications

• 2016, Monthly Notices of the Royal Astronomical Society, 459, 2432
  Veltchev, T. V.. Donkov, S., Klessen, R. S.
  
• 2017, Bulgarian Astronomical Journal, 27, 64
  Veltchev, T V, Donkov, S., Stanchev, O.
  
• 2017, Monthly Notices of the Royal Astronomical Soci­ ety, 466, 914
  Donkov, S., Veltchev, T. V., Klessen, R. S.
  
• 2018, Astronomical & Astrophysical Transactions, 30, 431
  Stanchev, O., Veltchev, T V, Donkov, S.
  
• 2018, Monthly Notices of the Royal Astronomical Society, 475, 2215
  Veltchev, T. V., Ossenkopf-Okada, V., Stanchev, O., Schneider, N., Donkov, S., Klessen, R. S.