%0 Generic %1 seifried2023origin %A Seifried, Daniel %A Walch, Stefanie %A Balduin, Thorsten %D 2023 %K dust %T On the origin of V-shaped polarisation spectra in molecular clouds %U http://arxiv.org/abs/2310.17211 %X In this work we extend previous theoretical works to gain a better understanding of the origin of recently observed polarisation degree spectra of molecular clouds, which show a so-called V-shape, i.e. a pronounced minimum around 350 $\mu$m. For this purpose, we present results of semi-analytical dust polarisation models. We benchmark our model against dust polarisation radiative transfer calculations performed with POLARIS. We show that V-shaped polarisation spectra can only be obtained if two dust phases, one dense and cold and one warm and dilute phase, are present along the line of sight. In contrast to previous results, no correlation between the alignment efficiency of silicate grains and the dust temperature is required; carbon grains are assumed to be not aligned with the magnetic field. We find that the V-shape is the stronger pronounced the larger the density and temperature contrast between both phases is. Moreover, the destruction of carbon grains by UV radiation in the warm and dilute phase leads to a significantly more pronounced V-shape in the polarisation spectrum. Reducing the alignment efficiency in the cold and dense phase also results in a more pronounced V-shape, its effect, however, is smaller than that of the UV-induced carbon grain destruction. Furthermore, we present a first, self-consistent polarisation spectrum obtained from a 3D, magneto-hydrodynamical molecular cloud simulation. The spectrum matches well with our semi-analytical prediction demonstrating the potential of such complex 3D simulations to study polarisation spectra. Comparing our model results with actual observations indicates that carbon grain destruction in illuminated regions might be required to match these observations. Reducing the alignment efficiency of silicate grains in the cold and dense phase would further improve the match between both data, however, it appears to not be a necessity.

@misc{seifried2023origin, abstract = {In this work we extend previous theoretical works to gain a better understanding of the origin of recently observed polarisation degree spectra of molecular clouds, which show a so-called V-shape, i.e. a pronounced minimum around 350 $\mu$m. For this purpose, we present results of semi-analytical dust polarisation models. We benchmark our model against dust polarisation radiative transfer calculations performed with POLARIS. We show that V-shaped polarisation spectra can only be obtained if two dust phases, one dense and cold and one warm and dilute phase, are present along the line of sight. In contrast to previous results, no correlation between the alignment efficiency of silicate grains and the dust temperature is required; carbon grains are assumed to be not aligned with the magnetic field. We find that the V-shape is the stronger pronounced the larger the density and temperature contrast between both phases is. Moreover, the destruction of carbon grains by UV radiation in the warm and dilute phase leads to a significantly more pronounced V-shape in the polarisation spectrum. Reducing the alignment efficiency in the cold and dense phase also results in a more pronounced V-shape, its effect, however, is smaller than that of the UV-induced carbon grain destruction. Furthermore, we present a first, self-consistent polarisation spectrum obtained from a 3D, magneto-hydrodynamical molecular cloud simulation. The spectrum matches well with our semi-analytical prediction demonstrating the potential of such complex 3D simulations to study polarisation spectra. Comparing our model results with actual observations indicates that carbon grain destruction in illuminated regions might be required to match these observations. Reducing the alignment efficiency of silicate grains in the cold and dense phase would further improve the match between both data, however, it appears to not be a necessity.}, added-at = {2023-10-27T14:28:02.000+0200}, author = {Seifried, Daniel and Walch, Stefanie and Balduin, Thorsten}, biburl = {https://www.bibsonomy.org/bibtex/29a6d898f66b54762b095a095c6538638/fboulang}, interhash = {53b3b0f828d693662f22295a14578e54}, intrahash = {9a6d898f66b54762b095a095c6538638}, keywords = {dust}, note = {cite arxiv:2310.17211Comment: 15 pages including appendix, 11 figures, submitted to A&A, comments are welcome}, timestamp = {2023-10-27T14:28:02.000+0200}, title = {On the origin of V-shaped polarisation spectra in molecular clouds}, url = {http://arxiv.org/abs/2310.17211}, year = 2023 }