Midterm Colloquium by Jonathan Oftedahl Vivanco – Niels Bohr Institutet - Københavns Universitet

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Midterm Colloquium by Jonathan Oftedahl Vivanco

It is known from polarized thermal dust emission and Zeeman splitting of spectral lines, that magnetic field are present in molecular clouds and pre-stellar cores thus dictating the evolution of star formation. The existence of massive disks around protostars, already at their earliest stages, is known from a number of high-resolution observations of the thermal dust continuum emission of Class 0 and Class I sources.

Recent magnetohydrodynamical simulations confirm that disks can form at these early stages, and that the evolution of the disk and proto-star is dictated by the strength of the magnetic field and how effective it is in regulating the dynamics during star formation. Using MHD simulations and radiative transfer codes to produce spectral energy density plots ( SED's), Commerҫon et al. (2012a) investigated the evolution in time around prestellar cores for 3 different magnetization levels. As in earlier simulations by other groups, their simulation produced disks and bipolar molecular outflows for the magnetized cases and fragmentation (multiple objects) and no disk in the low-magnetization case. When looking at the SED's for the three cases, the moderate magnetization showed no evolution at all, while the other two, although showing some evolution, were almost similar during the whole simulation. Their conclusion is that
the SED is not a useful tracer of disk formation and the magnetic field.

Another way of treating this is by looking at the polarized dust continuum emission. As nonspherical rotating dust particles align their rotation axis along the direction of the local magnetic field, and because the emitted radiation is stronger along the longest dust particle axis, we observe polarized thermal emission whenever there is a magnetic field. In my thesis I am trying to use MHD simulations and radiative transport code of early protostars to produce synthetic polarization images that can be processed to the get maps of the magnetic field lines around these objects and how they evolve. In this way it can be possible, by comparing simulations with observations, to identify the evolutionary phase of an observed sources as well as constrain the dynamics of them. The high resolution of the ALMA interferometer and its capability of making polarization observations, will enable us to look at magnetic fields for star formation at unprecedented detail, and thus creating the
link between numerical simulations and observations.