Abstract Details

Name: Atanu Koley
Affiliation: PhD student, Indian Institute of Science, Bangalore-560012
Conference ID: ASI2021_594
Title : The magnetic field in dense photodissociation region of DR21
Authors and Co-Authors : Atanu Koley, 5th year PhD student, Indian Institute of Science, Bangalore- 560012. Nirupam Roy, Assistant Professor, Indian Institute of Science, Bangalore -560012. Karl M Menten, Professor, Max Planck Institute for Radioastronomy, Bonn Germany. Arshia M Jacob, PhD student, Max Planck Institute for Radioastronomy, Bonn Germany. Thushara G. S. Pillai, Senior Research Scientist, Boston University, USA. Micheal R. Rugel, Post doctoral fellow, Max Planck Institute for Radioastronomy, Bonn Germany.
Abstract Type : Oral
Abstract Category : Stars, ISM and Galaxy
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 HII region DR 21 (Main). From the OH 18 cm absorption, observed withthe 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 toward the neighbouring DR 21(OH) and W 75S-FR1 regions also exhibit the Zeeman splitting. Along with the OH data, we use [CII] 158μm 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 and1667 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 mag-netic 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.