The magnetic field in the dense photodissociation region of DR 21

Abstract

Measuring interstellar magnetic fields is extremely important for understanding their role in different evolutionary stages of interstellar clouds and of star formation. However, detecting the weak field is observationally challenging. We present measurements of the Zeeman effect in the 1665 and 1667~MHz (18~cm) lines of the hydroxyl radical (OH) lines toward the dense photodissociation region (PDR) associated with the compact H{\sc ii} region DR~21~(Main). From the OH 18~cm absorption, observed with the Karl G. Jansky Very Large Array, we find that the line of sight magnetic field in this region is $\sim 0.13$~mG. The same transitions in maser emission toward the neighboring DR~21(OH) and W~75S-FR1 regions also exhibit the Zeeman splitting. Along with the OH data, we use [C{\sc ii}] 158 $\mu$m line and hydrogen radio recombination line data to constrain the physical conditions and the kinematics of the region. We find the OH column density to be $\sim 3.6\times 10^{16}(T_{\mathrm{ex}}/25\mathrm{K}){\mathrm{cm}}^{-2}$, and that the 1665 and 1667 MHz absorption lines are originating from the gas where OH and C${}^{+}$ are co-existing in the PDR. Under reasonable assumptions, we find the measured magnetic field strength for the PDR to be lower than the value expected from the commonly discussed density--magnetic field relation while the field strength values estimated from the maser emission are roughly consistent with the same. Finally, we compare the magnetic field energy density with the overall energetics of DR~21's PDR and find that, in its current evolutionary stage, the magnetic field is not dynamically important.

arXiv comment13 pages with 14 figures and 3 tables; version accepted for publication in MNRAS

References in corpus (33)

• Control of star formation by supersonic turbulence
• A Super-Alfvenic Model of Dark Clouds
• Dynamic star formation in the massive DR21 filament
• Parallaxes and proper motions of interstellar masers toward the Cygnus X star-forming complex. I. Membership of the Cygnus X region
• The earliest phases of high-mass star formation: a 3 square degree millimeter continuum mapping of Cygnus X
• The spine of the swan: A Herschel study of the DR21 ridge and filaments in Cygnus X
• Radiation-magnetohydrodynamic simulations of HII regions and their associated PDRs in turbulent molecular clouds
• Collapse-Driven Outflow in Star-Forming Molecular Cores
• A retrospective view of Miriad
• Full-Polarization Observations of OH Masers in Massive Star-Forming Regions: I. Data
• Full-Polarization Observations of OH Masers in Massive Star-Forming Regions: II. Maser Properties and the Interpretation of Polarization
• Interstellar Hydroxyl Masers in the Galaxy. II. Zeeman Pairs and the Galactic Magnetic Field
• Probing the Magnetic Field with Molecular Ion Spectra
• Probing the Magnetic Field with Molecular ion Spectra. II
• A technique for constraining the driving scale of turbulence and a modified Chandrasekhar-Fermi method
• Protostar Formation in Magnetic Molecular Clouds beyond Ion Detachment: II. Typical Axisymmetric Solution
• Dual Cometary HII Regions in DR21: Bow Shocks or Champagne Flows?
• Testing Molecular-Cloud Fragmentation Theories: Self-Consistent Analysis of OH Zeeman Observations
• Cloud-cloud collision in the DR 21 cloud as a trigger of massive star formation
• Magnetic fields in molecular clouds: Limitations of the analysis of Zeeman observations
• VLA OH and H I Zeeman Observations of the NGC 6334 Complex
• DR21 Main: A Collapsing Cloud
• The Super-Alfvénic Model of Molecular Clouds: Predictions for Mass-to-Flux and Turbulent-to-Magnetic Energy Ratios
• HIFI observations of warm gas in DR21: Shock versus radiative heating
• Turbulence measurements from HI absorption spectra
• Enhanced density and magnetic fields in interstellar OH masers
• Orion's Veil: Magnetic field strengths and other properties of a PDR in front of the Trapezium Cluster
• Herschel-SPIRE spectroscopy of the DR21 molecular cloud core
• The Zeeman Effect in the 44 GHz Class I Methanol Maser Line toward DR21(OH)
• The cometary HII regions of DR 21: Bow shocks or champagne flows or both?
• Estimating kinetic temperature from H I 21 cm absorption studies: correction for the turbulence broadening
• Star Formation in Molecular Clouds
• Magnetic Field Strengths in Photodissociation Regions

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