Universität zu Köln

Seifried, D. ORCID: 0000-0002-0368-9160, Walch, S. ORCID: 0000-0001-6941-7638 and Balduin, T. ORCID: 0000-0003-2652-5457 (2025). On the origin of V-shaped polarization spectra in molecular clouds. Monthly Notices of the Royal Astronomical Society, 542 (4). pp. 3302-3314. Oxford University Press. ISSN 0035-8711

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Abstract

We extend previous theoretical works to gain a better understanding of the origin of observed polarization 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 the results of two-phase dust models investigated with polaris. We also provide a guideline to calculate individual dust temperatures for different grain types in polaris. We show that V-shaped polarization spectra can only be obtained if two dust phases, one dense and cold as well as one warm and dilute phase, are present along the line of sight. We find that the V-shape becomes more pronounced as the density and temperature contrast between the two phases increases. In contrast to previous results, no correlation between the alignment efficiency of silicate grains and the dust temperature is required; carbonaceous grains are, in general, assumed to be unaligned with the magnetic field. By matching our model results with actual observations of V-shaped polarization spectra, we show that in ultraviolet-illuminated regions (here, the warm and dilute phase), carbon grain destruction might take place. This leads to a more pronounced V-shape with a minimum around 300 $\mu$m. In addition, we show that the dust spectral index and temperature of silicate grains affect the steepness of the polarization spectrum at long wavelengths. Finally, we present a first polarization spectrum obtained from a 3D magnetohydrodynamical molecular cloud simulation. It shows a flattening or even weakly pronounced minimum around 350 $\mu$m, demonstrating the potential of such complex 3D simulations to study polarization spectra.

Item Type:	Article
Creators:	Creators Email ORCID ORCID Put Code Seifried, D. UNSPECIFIED https://orcid.org/0000-0002-0368-9160 UNSPECIFIED Walch, S. UNSPECIFIED https://orcid.org/0000-0001-6941-7638 UNSPECIFIED Balduin, T. UNSPECIFIED https://orcid.org/0000-0003-2652-5457 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-811310
Identification Number:	10.1093/mnras/staf1423
Journal or Publication Title:	Monthly Notices of the Royal Astronomical Society
Volume:	542
Number:	4
Page Range:	pp. 3302-3314
Number of Pages:	13
Date:	October 2025
Publisher:	Oxford University Press
ISSN:	0035-8711
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Physics > Institute of Physics I
Subjects:	Physics
Uncontrolled Keywords:	Keywords Language MHD – polarization – radiative transfer – methods: numerical – ISM: clouds – dust, extinction English
['eprint_fieldname_oa_funders' not defined]:	Publikationsfonds UzK
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/81131