Distance, magnetic field, and kinematics of the filamentary cloud LDN 1157

¹ Indian Institute of Astrophysics, Koramangala, Bangalore 560034, India
e-mail: ekta.sharma@iiap.res.in
² Department of Physics and Astrophysics, University of Delhi, Delhi 110007, India
³ SOFIA Science Centre, USRA, NASA Ames Research Centre, MS-12, N232, Moffett Field, CA 94035, USA
⁴ Korea Astronomy & Space Science Institute, 776 Daedeokdae-ro, Yuseong-gu, Daejeon, Republic of Korea
⁵ University of Science and Technology, Korea, 217 Gajeong-ro, Yuseong-gu, Daejeon 34113, Republic of Korea
⁶ School of Physical Sciences, National Institute of Science Education and Research, HBNI, Jatni 752050, Odisha, India
⁷ Indian Institute of Space Science and Technology, Valiamala PO, Thiruvananthapuram - 695547 Kerala, India
⁸ School of Space Research, Kyung-Hee University, 1732, Deogyeong-daero, Giheung-gu, Yongin-si, Gyeonggi-do 17104, Republic of Korea
⁹ Nobeyama Radio Observatory, National Astronomical Observatory of Japan, National Institutes of Natural Sciences, Nobeyama, Minamimaki, Minamisaku, Nagano 384-1305, Japan

Received: 2 January 2020
Accepted: 27 March 2020

Abstract

Context. LDN 1157 is one of several clouds that are situated in the cloud complex LDN 1147/1158. The cloud presents a coma-shaped morphology with a well-collimated bipolar outflow emanating from a Class 0 protostar, LDN 1157-mm, that resides deep inside the cloud.

Aims. The main goals of this work are (a) mapping the intercloud magnetic field (ICMF) geometry of the region surrounding LDN 1157 to investigate its relationship with the cloud morphology, outflow direction, and core magnetic field (CMF) geometry inferred from the millimeter- and submillimeter polarization results from the literature, and (b) to investigate the kinematic structure of the cloud.

Methods. We carried out optical (R-band) polarization observations of the stars projected on the cloud to map the parsec-scale magnetic field geometry. We made spectroscopic observations of the entire cloud in the ¹²CO, C¹⁸O, and N₂H⁺ (J = 1–0) lines to investigate its kinematic structure.

Results. We obtained a distance of 340 ± 3 pc to the LDN 1147/1158, complex based on the Gaia DR2 parallaxes and proper motion values of the three young stellar objects (YSOs) associated with the complex. A single filament of ~1.2 pc in length (traced by the Filfinder algorithm) and ~0.09 pc in width (estimated using the Radfil algorithm) is found to run throughout the coma-shaped cloud. Based on the relationships between the ICMF, CMF, filament orientations, outflow direction, and the hourglass morphology of the magnetic field, it is likely that the magnetic field played an important role in the star formation process in LDN 1157. LDN 1157-mm is embedded in one of the two high-density peaks detected using the Clumpfind algorithm. The two detected clumps lie on the filament and show a blue-red asymmetry in the ¹²CO line. The C¹⁸O emission is well correlated with the filament and presents a coherent structure in velocity space. Combining the proper motions of the YSOs and the radial velocity of LDN 1147/1158 and an another complex, LDN 1172/1174, that is situated ~2° east of it, we found that the two complexes are moving collectively toward the Galactic plane. The filamentary morphology of the east-west segment of LDN 1157 may have formed as a result of mass lost by ablation through interaction of the moving cloud with the ambient interstellar medium.