Grain Alignment in Turbulent Cores

Abstract

The Interstellar Medium (ISM) is strongly magnetized therefore magnetic fields are important to its evolution. The morphology of the interstellar field can be mapped using polarized emission from large asymmetric silicate grains that are aligned with their long axis perpendicular to the magnetic field as well as through polarized extinction of background sources by the same grains. The grains are spun-up and subsequently aligned via Radiative Alignment Torques (RAT) due to anisotropic radiation from the Interstellar Radiation Field (ISRF) or a localized source such as a protostar. Deep inside starless cores the ISRF is highly reddened and therefore grains can not be aligned by it. We examine if the growth of large grains $a_{max} > 10 \mu m$ or a warm central source $T <90K$ can enhance alignment to detectable levels. We found that while both large grains $a_{max} = 10 \mu m, 100 \mu m $ and an embedded protostar with $T_{\star} = 30K-90K$ enhance the fraction of aligned grains deep in the core this enhancement did not translate to a significant enhancement of the polarized fraction in emission and extinction. This is because the enhancement at most brings the normalized fraction of aligned grains from $0.01$ to $0.10$ which is likely undetectable considering that the polarization limit for maximally aligned grains is only $7\%$ in extinction and $15\%$ in emission.