Efeitos da transferência radiativa em diferentes técnicas de rastreamento do campo magnético no meio interestelar

Abstract

Probing magnetic fields in molecular clouds is typically difficult, even with the use of polarimetry. Newtechniques have been developed to track magnetic fields in turbulent media using velocity channel maps, which can be obtained by common spectrometers. In this thesis, we study magnetohydrodynamic turbulence based on simulations of high resolution three-dimensional data cubes representing optically thick interstellar media, in order to obtain calibrations that allow mapping the magnetic field of real environments. Ten complete high-resolution data cubes, containing position-position-velocity (PPV) maps with a resolution of 7923, were produced with the ZEUS-MP/3D code. The cubes simulate emission lines of the isotopes 12CO, 13CO and C18O from synthetic molecular clouds and include the radiative transfer processes. The conditions for the medium are from single-fluid isothermal magnetohydrodynamic simulations with forced agitation. Three techniques that allow tracking the morphology of the magnetic field without polarimetry were tested: correlation function anisotropy (CFA), principal component analysis of anisotropies (PCAA), and velocity gradient technique (VGT). Previous studies have tested these techniques using low resolution numerical data for optically thin media and high resolution non-periodic subblocks for optically thick media. This thesis represents a new study whose scaling parameters applied to high-resolution full data cubes improve the accuracy of magnetic field measurement. This new analysis shows that, in the presence of absorption, the VGT and CFA techniques can successfully track the orientation of moderate and thick magnetic fields, which is in agreement with the low resolution numerical results obtained for optically thin media. The anisotropy of the turbulence vortices tends to vary both with the change of the Alfvenic Mach number and with the velocity channel. However, a preferred direction for anisotropy manifests itself when we treat the same velocity channel with non-zero modulus for 13CO and C18O, whereas when the modulus of velocity is close to zero, 12CO and C18O are the preferred direction. Similar to previous simulations of optically thin media, our results show that the PCCA technique is also well viable for the study of optically thick media. We can conclude that the technique that best explains the various cases we analyzed is VGT, in which it can better explain the magnetic field for the most diverse characteristics of a medium. However, all magnetic field tracking techniques require adjustments.