The Densities and Dynamics of Molecular Clouds in Spiral Galaxies

UoM administered thesis: Master of Science by Research

  • Authors:
  • Thomas Peasley


The densities and dynamics are studied of simulated molecular clouds extracted from two galaxy scale simulations using a modified version of the Arepo code (Smith et al, (in prep)). Three clouds are selected, a diffuse cloud with a target mass resolution of 1 solar masses, and two views of a more highly resolved cloud (target 0.25 solar masses) undergoing a spiral arm passage. These latter two grids are of the same gaseous region 10Myr apart. Molecular structures are identified in the grids through the use of the "Astrodendro" python package ( These structures and their respective 2D projections are analysed through the use of mass functions, probability density functions (PDF’s) and the relationship of the structure’s velocity dispersion to it’s scale and mass. In all cases of projection it is found that the structure mass and density distributions are affected by the line of sight. The 2D PDF’s of these structures are well described by a two step power law in all three cases, whilst a single power law best describes the PDF’s in the 3D case. Because of the lack of self-gravity in the simulations, the two step power laws are summised to be a projection effect. In some cases, Larson’s dispersion exponents were reproduced in agreement of observa- tion, but ultimately the scaling coefficients show the clouds to be under driven. This is concluded to be another effect of the lack of self-gravity, and not enough supernovae feedback distributed in the simulations, something that future work will address.


Original languageEnglish
Awarding Institution
Award date1 Aug 2019