Submillimeter Polarization of Galactic Clouds: A Comparison of 350 micron and 850 micron Data

TL;DR

This study compares polarization measurements at 350 and 850 microns in 17 Galactic clouds, revealing significant differences in polarization angles and amplitude ratios, and providing a large dataset for understanding dust grain properties.

Contribution

It presents a comprehensive comparison of dual-wavelength polarization data in a large sample of Galactic clouds, expanding previous work and offering new insights into dust grain characteristics.

Findings

64% of high S/N data show >10° difference in polarization angles between wavelengths

Median polarization amplitude ratio P(850)/P(350) = 1.7 +/- 0.6

Polarization decreases with increasing 850-to-350 micron intensity ratio

Abstract

The Hertz and SCUBA polarimeters, working at 350 micron and 850 micron respectively, have measured the polarized emission in scores of Galactic clouds. Of the clouds in each dataset, 17 were mapped by both instruments with good polarization signal-to-noise ratios. We present maps of each of these 17 clouds comparing the dual-wavelength polarization amplitudes and position angles at the same spatial locations. In total number of clouds compared, this is a four-fold increase over previous work. Across the entire data-set real position angle differences are seen between wavelengths. While the distribution of \phi(850)-\phi(350) is centered near zero (near-equal angles), 64% of data points with high polarization signal-to-noise (P >= 3\sigma_p) have |\phi(850)-\phi(350)| > 10 degrees. Of those data with small changes in position angle (<= 10 degrees) the median ratio of the polarization amplitudes is P(850)/P(350) = 1.7 +/- 0.6. This value is consistent with previous work performed on smaller samples and models which require mixtures of different grain properties and polarization efficiencies. Along with the polarization data we have also compiled the intensity data at both wavelengths; we find a trend of decreasing polarization with increasing 850-to-350 micron intensity ratio. All the polarization and intensity data presented here (1699 points in total) are available in electronic format.