Submillimeter and Far-Infrared Polarimetric Observations of Magnetic Fields in Star-Forming Regions (1904.04826v1)

Abstract: Observations of star-forming regions by the current and upcoming generation of submillimeter polarimeters will shed new light on the evolution of magnetic fields over the cloud-to-core size scales involved in the early stages of the star formation process. Recent wide-area and high-sensitivity polarization observations have drawn attention to the challenges of modeling magnetic field structure of star forming regions, due to variations in dust polarization properties in the interstellar medium. However, these observations also for the first time provide sufficient information to begin to break the degeneracy between polarization efficiency variations and depolarization due to magnetic field sub-beam structure, and thus to accurately infer magnetic field properties in the star-forming interstellar medium. In this article we discuss submillimeter and far-infrared polarization observations of star-forming regions made with single-dish instruments. We summarize past, present and forthcoming single-dish instrumentation, and discuss techniques which have been developed or proposed to interpret polarization observations, both in order to infer the morphology and strength of the magnetic field, and in order to determine the environments in which dust polarization observations reliably trace the magnetic field. We review recent polarimetric observations of molecular clouds, filaments, and starless and protostellar cores, and discuss how the application of the full range of modern analysis techniques to recent observations will advance our understanding of the role played by the magnetic field in the early stages of star formation.

Submillimeter and Far-Infrared Polarimetric Observations of Magnetic Fields in Star-Forming Regions

The paper of star-forming regions through polarimetric observations at submillimeter and far-infrared wavelengths offers invaluable insights into the evolution and characteristics of magnetic fields across varying scales. Pattle and Fissel (2019) provide an extensive review focusing on the contemporary instrumentation and techniques employed to analyze these observations, offering a detailed narrative on how these methodologies contribute to our understanding of star formation.

Submillimeter polarimetry is pivotal in discerning the magnetic field morphology in star-forming regions. The process utilizes the alignment of asymmetric dust grains perpendicular to the magnetic field lines, as outlined by early theories such as Davis and Greenstein (1951). This alignment results in polarized thermal emission from the dust, which can be captured and analyzed to infer magnetic field properties.

Instrumentation and Observational Strategies

The paper presents an overview of single-dish polarimetric instruments used in these observations, such as JCMT, CSO, and APEX among others. These instruments have undergone significant improvements, particularly in terms of mapping speed and sensitivity. The range of wavelengths they cover allows researchers to probe distinct environments within star-forming regions, from molecular clouds to protostellar cores.

Pattle and Fissel also detail current and forthcoming polarimeters, emphasizing innovations such as the TolTEC camera, which harnesses kinetic inductance detectors. The implementation of sophisticated detectors like TES bolometers in instruments such as SOFIA/HAWC+ is transforming submillimeter polarimetry by providing higher resolution and broader coverage.

Techniques for Interpretation

To interpret polarization observations, various methods have been postulated, including the Davis-Chandrasekhar-Fermi (DCF) technique used to estimate magnetic field strength. The authors discuss the inherent challenges and continued evolution of these methodologies, including corrections for sub-beam effects and the importance of numerical simulations to provide synthetic observations for comparison.

The Histogram of Relative Orientations (HRO), highlighted in the review, is crucial for understanding the dynamic interrelation between magnetic fields and gaseous structures. The paper emphasizes how changes in grain alignment and depolarization at high densities present complications that must be addressed with nuanced approaches.

Molecular Clouds and Filaments

The paper meticulously reviews polarimetric observations of large molecular clouds and the intriguing dynamics within filaments. Findings from Planck and BLASTPol provide a comprehensive view of how magnetic fields influence the morphology and evolution of clouds. These observations suggest that magnetic fields often dictate the layout of lower-density structures and play a potentially regulatory role in star formation processes within filaments.

Implications and Future Directions

Pattle and Fissel propose that advancements in polarimetry, aided by next-generation terrestrial and space-based instruments, will yield more precise and expansive mappings of magnetic field structures. They speculate that these developments will facilitate a deeper understanding of magnetic fields in a variety of star-forming environments.

This detailed review underscores the necessity for continued development in polarimetric techniques and instrumentation, enabling researchers to disentangle the complex interplay between magnetic fields and interstellar matter during star formation. Future research prompted by this paper can be expected to address remaining uncertainties and refine models of star formation, leveraging the capabilities of new observatories and advancements in analytic methodologies such as Bayesian approaches to grain alignment. This body of work signifies a substantial step towards comprehensively understanding the magnetic framework underlying star-forming regions, from the micro-scale dynamics in protostellar cores to the macro-scale interactions in filamentary clouds.