Relative Alignment Between Magnetic Fields and Molecular Gas Structure in Molecular Clouds
arXiv:2303.07410 · doi:10.1093/mnras/stad733
Abstract
We compare the structure of synthetic dust polarization with synthetic molecular line emission from radiative transfer calculations using a 3-dimensional, turbulent collapsing-cloud magnetohydrodynamics simulation. The histogram of relative orientations (HRO) technique and the projected Rayleigh statistic (PRS) are considered. In our trans-Alfvénic (more strongly magnetized) simulation, there is a transition to perpendicular alignment at densities above cm. This transition is recovered in most of our synthetic observations of optically thin molecular tracers, however for CO it does not occur and the PRS remains in parallel alignment across the whole observer-space. We calculate the physical depth of the optical depth surface and find that for CO it is largely located in front of the cloud midplane, suggesting that CO is too optically thick and instead mainly probes low volume density gas. In our super-Alfvénic simulation, the magnetic field becomes significantly more tangled, and all observed tracers tend toward no preference for perpendicular or parallel alignment. An observable difference in alignment between optically thin and optically thick tracers may indicate the presence of a dynamically important magnetic field, though there is some degeneracy with viewing angle. We convolve our data with a Gaussian beam and compare it with HRO results of the Vela C molecular cloud. We find good agreement between these results and our sub-Alfvénic simulations when viewed with the magnetic field in the plane-of-the-sky (especially when sensitivity limitations are considered), though the observations are also consistent with an intermediately inclined magnetic field.
arXiv comment18 pages, 13 figures, accepted for publication in MNRAS
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