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Title: Effects of grain alignment efficiency on synthetic dust polarization observations of molecular clouds

Abstract

ABSTRACT It is well known that the polarized continuum emission from magnetically aligned dust grains is determined to a large extent by local magnetic field structure. However, the observed significant anticorrelation between polarization fraction and column density may be strongly affected, perhaps even dominated by variations in grain alignment efficiency with local conditions, in contrast to standard assumptions of a spatially homogeneous grain alignment efficiency. Here we introduce a generic way to incorporate heterogeneous grain alignment into synthetic polarization observations of molecular clouds (MCs), through a simple model where the grain alignment efficiency depends on the local gas density as a power law. We justify the model using results derived from radiative torque alignment theory. The effects of power-law heterogeneous alignment models on synthetic observations of simulated MCs are presented. We find that the polarization fraction-column density correlation can be brought into agreement with observationally determined values through heterogeneous alignment, though there remains degeneracy with the relative strength of cloud-scale magnetized turbulence and the mean magnetic field orientation relative to the observer. We also find that the dispersion in polarization angles-polarization fraction correlation remains robustly correlated despite the simultaneous changes to both observables in the presence of heterogeneous alignment.

Authors:
ORCiD logo [1];  [2];  [3];  [2]
  1. Department of Astronomy, University of Virginia, Charlottesville, VA 22904, USA, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA
  2. Department of Astronomy, University of Virginia, Charlottesville, VA 22904, USA
  3. National Radio Astronomy Observatory, Charlottesville, VA 22903, USA
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
1572435
Grant/Contract Number:  
AC52-07NA27344; LLNL-JRNL-764043
Resource Type:
Published Article
Journal Name:
Monthly Notices of the Royal Astronomical Society
Additional Journal Information:
Journal Name: Monthly Notices of the Royal Astronomical Society Journal Volume: 490 Journal Issue: 2; Journal ID: ISSN 0035-8711
Publisher:
Oxford University Press
Country of Publication:
United Kingdom
Language:
English

Citation Formats

King, Patrick K., Chen, Che-Yu, Fissel, L. M., and Li, Zhi-Yun. Effects of grain alignment efficiency on synthetic dust polarization observations of molecular clouds. United Kingdom: N. p., 2019. Web. doi:10.1093/mnras/stz2628.
King, Patrick K., Chen, Che-Yu, Fissel, L. M., & Li, Zhi-Yun. Effects of grain alignment efficiency on synthetic dust polarization observations of molecular clouds. United Kingdom. doi:10.1093/mnras/stz2628.
King, Patrick K., Chen, Che-Yu, Fissel, L. M., and Li, Zhi-Yun. Sat . "Effects of grain alignment efficiency on synthetic dust polarization observations of molecular clouds". United Kingdom. doi:10.1093/mnras/stz2628.
@article{osti_1572435,
title = {Effects of grain alignment efficiency on synthetic dust polarization observations of molecular clouds},
author = {King, Patrick K. and Chen, Che-Yu and Fissel, L. M. and Li, Zhi-Yun},
abstractNote = {ABSTRACT It is well known that the polarized continuum emission from magnetically aligned dust grains is determined to a large extent by local magnetic field structure. However, the observed significant anticorrelation between polarization fraction and column density may be strongly affected, perhaps even dominated by variations in grain alignment efficiency with local conditions, in contrast to standard assumptions of a spatially homogeneous grain alignment efficiency. Here we introduce a generic way to incorporate heterogeneous grain alignment into synthetic polarization observations of molecular clouds (MCs), through a simple model where the grain alignment efficiency depends on the local gas density as a power law. We justify the model using results derived from radiative torque alignment theory. The effects of power-law heterogeneous alignment models on synthetic observations of simulated MCs are presented. We find that the polarization fraction-column density correlation can be brought into agreement with observationally determined values through heterogeneous alignment, though there remains degeneracy with the relative strength of cloud-scale magnetized turbulence and the mean magnetic field orientation relative to the observer. We also find that the dispersion in polarization angles-polarization fraction correlation remains robustly correlated despite the simultaneous changes to both observables in the presence of heterogeneous alignment.},
doi = {10.1093/mnras/stz2628},
journal = {Monthly Notices of the Royal Astronomical Society},
number = 2,
volume = 490,
place = {United Kingdom},
year = {2019},
month = {9}
}

Journal Article:
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This content will become publicly available on September 21, 2020
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