B-fields And dust in interstelLar fiLAments using Dust POLarization (BALLAD-POL): III. Grain alignment and disruption mechanisms in G34.43+0.24 using polarization observations from JCMT/POL-2

arXiv (Cornell University)

Abstract

Polarization of starlight and thermal dust emission due to aligned non-spherical grains helps us to trace magnetic field (B-field) morphology in molecular clouds and to study grain alignment mechanisms. In this work, we study grain alignment and disruption mechanisms in a filamentary infrared dark cloud G34.43+0.24 using thermal dust polarization observations from JCMT/POL-2 at 850 $μ\text{m}$. We study in three sub-regions as North harboring MM3 core, Center harboring MM1 and MM2 cores and South having no core. We find the decrease in polarization fraction P with increasing total intensity and gas column density, known as polarization hole. To disentangle the effect of magnetic field tangling on the polarization hole, we estimate the polarization angle dispersion function. We find depolarizations in North and Center regions are due to decrease in net alignment efficiency of grains but in South region, effect of magnetic field tangling is significant to cause depolarization. To test whether RAdiative Torque (RAT) mechanism can reproduce the observational data, we calculate minimum alignment and disruption sizes of grains using RAT theory and our study finds that RAT alignment mechanism can explain the depolarizations in North and Center regions where B-field tangling effect is less important, except for core regions. We find hints of RAdiative Torque Disruption (RAT-D) in the core regions of MM3 in North, MM1 and MM2 in Center. We also find that the high P value of around 8-20% in the outer regions of the filament can be explained potentially by magnetically enhanced RAT alignment mechanism.

Authors 6

1. Saikhom Pravash

   Indian Institute of Astrophysics · Pondicherry University

   Affiliation as printed

   Indian Institute of Astrophysics , II Block , Koramangala , 560034 , India;

   Pondicherry University, R.V. Nagar , Kalapet , Puducherry , 605014 , India

2. Archana Soam

   Indian Institute of Astrophysics

   Affiliation as printed

   Indian Institute of Astrophysics , II Block , Koramangala , 560034 , India;

3. Pham Ngoc Diep

   Graduate University of Science and Technology · Trung tâm Vũ trụ Việt Nam · Vietnam Academy of Science and Technology

   Affiliation as printed

   Department of Astrophysics , Vietnam National Space Center , Vietnam Academy of Science and Technology , 18 Hoang Quoc Viet , Hanoi , Vietnam

   Graduate University of Science and Technology , Vietnam Academy of Science and Technology , 18 Hoang Quoc Viet , Hanoi , Vietnam

4. Thiem Hoang

   Korea Astronomy and Space Science Institute · Korea University of Science and Technology

   Affiliation as printed

   Korea Astronomy and Space Science Institute , 776 Daedeokdae-ro , Yuseong-gu , Daejeon 34055 , Republic of Korea

   University of Science and Technology , Korea , 217 Gajeong-ro , Yuseong-gu , Daejeon 34113 , Republic of Korea

5. Nguyen Bich Ngoc
6. Le Ngoc Tram Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory , Leiden University , PO Box 9513 , 2300 RA Leiden , The Netherlands