Modeling the Far-Infrared Polarization Spectrum of a High-Mass Star Forming Cloud

TL;DR

This study models the far-infrared polarization spectrum of a high-mass star forming cloud, revealing that temperature-dependent grain alignment explains observed spectral features better than other models.

Contribution

It introduces a temperature-dependent grain alignment model that successfully reproduces the observed falling polarization spectrum in a star forming cloud.

Findings

Temperature-dependent alignment produces a falling spectrum consistent with observations.

No correlation between temperature and polarization spectrum slope.

Positive correlation between column density and spectrum slope.

Abstract

The polarization spectrum, or wavelength dependence of the polarization fraction, of interstellar dust emission provides important insights into the grain alignment mechanism of interstellar dust grains. We investigate the far-infrared polarization spectrum of a realistic simulated high-mass star forming cloud under various models of grain alignment and emission. We find that neither a homogeneous grain alignment model nor a grain alignment model that includes collisional dealignment is able to produce the falling spectrum seen in observations. On the other hand, we find that a grain alignment model with grain alignment efficiency dependent on local temperature is capable of producing a falling spectrum that is in qualitative agreement with observations of OMC-1. For the model most in agreement with OMC-1, we find no correlation between temperature and the slope of the polarization spectrum. However, we do find a positive correlation between column density and the slope of the polarization spectrum. We suggest this latter correlation to be the result of wavelength-dependent polarization by absorption.