EPoS Contribution
EPoS Contribution
Can the Virial Parameter Reliably Trace the Dynamical State of Molecular Clouds?

Camilo Penaloza
Cardiff U, Cardiff, UK
One of the "standard archetypes" of star formation is that stars are formed in long lived, bound molecular clouds. This paradigm comes from examining the virial parameter of molecular clouds. To calculate the virial parameter we rely on three quantities: velocity dispersion, size and mass, each of which have their own underlying assumptions, uncertainties and biases. It should come as no surprise that variations in these quantities can have a significant impact on our assessment of cloud dynamics and hence our overall understanding of star formation.
The aim of this work is to study how the dynamical state of clouds changes as a function of metallicity and to test how accurately the virial parameter traces these changes. In order to do this we performed a set of smooth particle hydrodynamics (SPH) simulations with time-dependent chemistry, in which metallicity was systematically varied. The simulations were then post-processed using radiative transfer (via RADMC-3D) to produce synthetic emission maps of 12CO.
In this talk I will present three main results. First I will show how the "observed" velocity dispersion significantly decreases with lower metallicities and how this is reflected on the virial parameter. Second I will highlight the importance of understanding the intrinsic assumptions that go into calculating the virial parameter, such as how the mass and radius are derived. Finally, I will show how the virial parameter of a cloud changes with metallicity and how the "observed" virial parameter compares to the "true" value in the simulation.
Caption: This plot shows the variability of the virial parameter when calculated using different methods. Clockwise: The first 3 values represent the virial parameter calculated from the numerical simulations and for different species. The rest of the values are calculated using the observationally derived virial equation and a different combinations of the velocity dispersion, R and M as derived from the synthetic observations. Finally each color represents clouds at different metallicities
Collaborators:
P.C. Clark, Cardiff U, UK
S.C.O. Glover, ITA, DE
Suggested Session: Molecular clouds