Probing interstellar grain growth through polarimetry in the Taurus cloud complex
Files
Accepted manuscript
Date
2020-12-23
Authors
Vaillancourt, John E.
Andersson, B. - G.
Clemens, Dan P.
Piirola, Vilppu
Hoang, Thiem
Becklin, Eric E.
Caputo, Miranda
Version
Accepted manuscript
OA Version
Citation
John E Vaillancourt, B.-.G. Andersson, Dan P Clemens, Vilppu Piirola, Thiem Hoang, Eric E Becklin, Miranda Caputo. "Probing Interstellar Grain Growth through Polarimetry in the Taurus Cloud Complex." The Astrophysical Journal, 2020, Volume 905, Issue 2, pp. 157 - 157. https://doi.org/10.3847/1538-4357/abc6b0
Abstract
The optical and near-infrared (OIR) polarization of starlight is typically understood to arise from the dichroic
extinction of that light by dust grains whose axes are aligned with respect to a local magnetic field. The size
distribution of the aligned grain population can be constrained by measurements of the wavelength dependence
of the polarization. The leading physical model for producing the alignment is that of radiative alignment torques
(RAT), which predicts that the most efficiently aligned grains are those with sizes larger than the wavelengths
of light composing the local radiation field. Therefore, for a given grain size distribution, the wavelength at
which the polarization reaches a maximum (𝛌max) should correlate with the characteristic reddening along the
line of sight between the dust grains and the illumination source. A correlation between 𝛌max and reddening
has been previously established for extinctions up to AV ≈ 4 mag. We extend the study of this relationship to a
larger sample of stars in the Taurus cloud complex, including extinctions AV > 10 mag. We confirm the earlier
results for AV < 4 mag, but find that the 𝛌max vs. AV relationship bifurcates above AV ≈ 4 mag, with part of the
sample continuing the previously observed relationship. The remaining sample exhibits a steeper rise in 𝛌max
vs. AV . We propose that the data exhibiting the steep rise represent lines of sight of high-density “clumps”,
where grain coagulation has taken place. We present RAT-based modeling supporting these hypotheses. These
results indicate that multi-band OIR polarimetry is a powerful tool for tracing grain growth in molecular clouds,
independent of uncertainties in the dust temperature and emissivity.
Description
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© 2020. The American Astronomical Society. All rights reserved.