Correlation between Interstellar Polarization and Dust Temperature: Alignment of Grains by Radiative Torques is Ubiquitous?

Abstract

We investigate the efficiency of interstellar polarization $p_{\lambda }/A_{\lambda }$ where $p_{\lambda }$ is the fractional linear polarization and $A_{\lambda }$ is extinction, in 16 lines of sight as a function of wavelength $\lambda$. We have used the data obtained with the low-dispersion spectropolarimeter HBS as well as those in literature. It is found that the polarization efficiency $p_{\lambda }/A_{\lambda }$ is proportional to $\exp (-\beta /\lambda )$ in wavelength $λ\approx 0.4-0.8 \micron$, where $\beta$ is a parameter which varies from 0.5 to 1.2 $\micron$. We find that $\beta$ is negatively correlated with the dust temperature deduced from infrared data by Schlegel et al., suggesting that the polarization efficiency is higher in short wavelength for higher temperature. According to the alignment theory by radiative torques (RATs), if the radiation is stronger and bluer, RATs will make small grains align better, and the polarization efficiency will increase in short wavelength. Our finding of the correlation between $\beta$ and the temperature is consistent with what is expected with the alignment mechanism by RATs.

5 pages, 3 figures. Accepted for publication in PASJ Letters, Vol.63, October 2011 issue

References in corpus (11)

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• Submillimeter Polarization of Galactic Clouds: A Comparison of 350 micron and 850 micron Data
• Modeling Grain Alignment by Radiative Torques and Hydrogen Formation Torques in Reflection Nebula
• Interstellar polarization and grain alignment: the role of iron and silicon
• The Magnetic Field of Cloud 3 in L204
• On the origins of polarization holes in Bok globules
• Probing the cold magnetized Universe with SPICA-POL (B-BOP)
• The Mechanical Alignment of Dust (MAD) I: On the spin-up process of fractal grains by a gas-dust drift
• Ultraviolet Spectropolarimetry with Polstar: Interstellar Medium Science
• SOFIA/HAWC+ observations of the Crab Nebula: dust properties from polarised emission