Koley, A and Roy, N and Menten, KM and Jacob, AM and Pillai, TGS and Rugel, MR (2021) The magnetic field in the dense photodissociation region of DR 21. In: Monthly Notices of the Royal Astronomical Society, 501 (4). pp. 4825-4836.
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Abstract
Measuring interstellar magnetic fields is extremely important for understanding their role in different evolutionary stages of interstellar clouds and 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 towards the dense photodissociation region (PDR) associated with the compact H 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 �0.13 mG. The same transitions in maser emission towards the neighbouring DR 21(OH) and W 75S-FR1 regions also exhibit the Zeeman splitting. Along with the OH data, we use C ii 158 μm 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 �3.6 � 1016(Tex/25 K) 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. © 2021 2020 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.
| Item Type: | Journal Article |
|---|---|
| Publication: | Monthly Notices of the Royal Astronomical Society |
| Publisher: | Oxford University Press |
| Additional Information: | The copyright of this article belongs to Oxford University Press |
| Department/Centre: | Division of Physical & Mathematical Sciences > Joint Astronomy Programme Division of Physical & Mathematical Sciences > Physics |
| Date Deposited: | 04 Mar 2021 10:27 |
| Last Modified: | 04 Mar 2021 10:27 |
| URI: | http://eprints.iisc.ac.in/id/eprint/68088 |
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