Bastian Körtgen — Page 2

arXiv2015

Impact Of Magnetic Fields On Molecular Cloud Formation & Evolution

We use magnetohydrodynamical simulations of converging flows to investigate the process of molecular cloud formation and evolution out of the magnetised ISM. Here, we investigate whether the observed subcritical HI clouds can become supercritical and hence allow the formation of stars within them. To do so, we vary the turbulent Mach number of the flows, as well as the initial magnetic field strength. We show that dense cores are able to build up under all conditions, but that star formation in these cores is either heavily delayed or completely suppressed if the initial field strength is B>3 microGauss. To probe the effect of magnetic diffusion, we introduce a tilting angle between the flows and the uniform background magnetic field, which mimics non--ideal MHD effects. Even with highly inclined flows, the formed cores are devoid of star formation, because no magnetically supercritical regions are build up. Hence we conclude, that the problem of how supercritical cloud cores are generated still persists.

astro-ph.GA↗

arXiv2015

Tracing the general structure of Galactic molecular clouds using Planck data: I. The Perseus region as a test case

We present an analysis of probability distribution functions (pdfs) of column density in different zones of the star-forming region Perseus and its diffuse environment based on the map of dust opacity at 353 GHz available from the Planck archive. The pdf shape can be fitted by a combination of a lognormal function and an extended power-law tail at high densities, in zones centred at the molecular cloud Perseus. A linear combination of several lognormals fits very well the pdf in rings surrounding the cloud or in zones of its diffuse neighbourhood. The slope of the mean density scaling law $\langleρ\rangle_L \propto L^α$ is steep ($α=-1.93$) in the former case and rather shallow ($α=-0.77\pm0.11$) in the rings delineated around the cloud. We interpret these findings as signatures of two distinct physical regimes: i) a gravoturbulent one which is characterized by nearly linear scaling of mass and practical lack of velocity scaling; and ii) a predominantly turbulent one which is best described by steep velocity scaling and by invariant for compressible turbulence $\langleρ\rangle_L u_L^3/L$, describing a scale-independent flux of the kinetic energy per unit volume through turbulent cascade. The gravoturbulent spatial domain can be identified with the molecular cloud Perseus while a relatively sharp transition to predominantly turbulent regime occurs in its vicinity.

astro-ph.GA↗