Monday, May 12, 2014 - 11:00am
Erik Bertram (ZAH/ITA):
"Principal Component Analysis of Molecular Clouds: Can CO reveal the dynamics?"
Abstract. Turbulence plays a fundamental role in the star formation process. Observations have shown that the velocity dispersion of molecular clouds is correlated with its size and mass, following a power-law. We use Principal Component Analysis (PCA) to measure the line width size relation and to study ISM dynamics in numerical simulations of typical molecular clouds with time-dependent chemical and radiative transfer. We investigate the slope of the pseudo structure function computed by PCA for individual chemical components: the total density, H2 density, 12CO density, 12CO J = 1 -> 0 intensity and 13CO J = 1 -> 0 intensity. We estimate power-law slopes for different chemical species that range from 0.5 to 1.4, in good agreement with observational results, and demonstrate that optical depth effects can influence the PCA. We show that when the PCA succeeds, the combination of chemical inhomogeneity and radiative transfer effects can influence the observed PCA slopes by as much as +/-0.1. The method can fail if the CO distribution is very intermittent, e.g. in low-density clouds where CO is confined to small fragments.