Magnetic Fields in Molecular Clouds

Recent observational evidence that magnetic fields are dynamically important in molecular clouds, compared to self-gravity and turbulence, is reviewed and illustrated with data from the NGC 2024 region. One piece of evidence, turbulence anisotropy, was found in the diffuse envelope of a cloud (Av~1; Heyer et al. 2008); our data further suggests turbulence anisotropy in the cloud (Av >7) and even near the cloud core (Av~100). The data also shows that magnetic fields can channe...

We demonstrate that the combination of Zeeman, polarimetry and ion-to-neutral molecular line width ratio measurements permits the determination of the magnitude and orientation of the magnetic field in the weakly ionized parts of molecular clouds. Zeeman measurements provide the strength of the magnetic field along the line of sight, polarimetry measurements give the field orientation in the plane of the sky and the ion-to-neutral molecular line width ratio determines the ang...

Most of the baryonic matter in the Universe is permeated by magnetic fields which affect many, if not most, of astrophysical phenomena both, in compact sources and in diffuse gas. Recent years have been marked by a worldwide surge of interest in the astrophysical magnetic fields, their origin, and their influence on the formation and evolution of astrophysical objects (stars, galaxies, cooling flows). This growing interest is in part due to the fact that it has become possibl...

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 tha...

Star formation is inefficient. Recent advances in numerical simulations and theoretical models of molecular clouds show that the combined effects of interstellar turbulence, magnetic fields and stellar feedback can explain the low efficiency of star formation. The star formation rate is highly sensitive to the driving mode of the turbulence. Solenoidal driving may be more important in the Central Molecular Zone, compared to more compressive driving agents in spiral-am clouds....

During the past decade the dynamical importance of magnetic fields in molecular clouds has been increasingly recognized, as observational evidence has accumulated. However, how a magnetic field affect star formation is still unclear. Typical star formation models still treat a magnetic fields as an isotropic pressure, ignoring the fundamental property of dynamically important magnetic fields: their direction. This study builds on our previous work which demonstrated how the m...

Magnetic fields pervade in the interstellar medium (ISM) and are believed to be important in the process of star formation, yet probing magnetic fields in star formation regions is challenging. We propose a new method to use Faraday rotation measurements in small scale star forming regions to find the direction and magnitude of the component of magnetic field along the line-of-sight. We test the proposed method in four relatively nearby regions of Orion A, Orion B, Perseus, a...

Observational evidence for strong magnetic fields throughout the envelopes of evolved stars is increasing. Many of the instruments coming on line in the near-future will be able to make further contributions to this field. Specifically, maser polarization observations and dust/line polarization in the sub-mm regime has the potential to finally provide a definite picture of the magnetic field strength and configuration from the Asymptotic Giant Branch (AGB) all the way to the ...

Magnetic fields are ubiquitously observed in the interstellar medium (ISM) of present-day star-forming galaxies with dynamically relevant energy densities. Using three-dimensional magneto-hydrodynamic (MHD) simulations of the supernova (SN) driven ISM in the flux-freezing approximation (ideal MHD) we investigate the impact of the magnetic field on the chemical and dynamical evolution of the gas, fragmentation and the formation of molecular clouds. We follow the chemistry with...

Of all the factors that influence star formation, magnetic fields are perhaps the least well understood. The goal of this paper is to characterize the 3D magnetic field properties of nearby molecular clouds through various methods of statistically analysing maps of polarized dust emission. Our study focuses on nine clouds, with data taken from the Planck Sky Survey as well as data from the Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry observations of Ve...