ALMA observations of massive clouds in the central molecular zone: slim filaments tracing parsec-scale shocks

¹ Department of Astronomy, School of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Rd., Minhang, Shanghai 200240, China
² School of Astronomy and Space Science, Nanjing University, 163 Xianlin Avenue, Nanjing 210023, China
³ Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education, Nanjing 210023, China
⁴ Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, China
⁵ Department of Astronomy, University of Florida, PO Box 112055, Gainesville, FL 32611, USA
⁶ Department of Physics, National Sun Yat-Sen University, No. 70, Lien-Hai Road, Kaohsiung City 80424, Taiwan
⁷ Center of Astronomy and Gravitation, National Taiwan Normal University, Taipei 116, Taiwan
⁸ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁹ Department of Astronomy, Xiamen University, Zengcuo’an West Road, Xiamen, 361005, China
¹⁰ Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
¹¹ Department of Physics and Astronomy, University of Kansas, 1251 Wescoe Hall Drive, Lawrence, KS 66045, USA
¹² UK ALMA Regional Centre Node, Jodrell Bank Centre for Astrophysics, The University of Manchester, Manchester M13 9PL, UK
¹³ Department of Physics, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
¹⁴ Department of Physics, University of Connecticut, 196A Auditorium Road, Storrs, CT 06269, USA
¹⁵ Astrophysics Research Institute, Liverpool John Moores University, IC2, Liverpool Science Park, 146 Brownlow Hill, Liverpool, L3 5RF, UK
¹⁶ Cosmic Origins Of Life (COOL) Research DAO, Munich, Germany
¹⁷ Xinjiang Astronomical Observatory, 150 Science 1-Street, Urumqi, Xinjiang 830011, China
¹⁸ University of Chinese Academy of Sciences, Beijing 100080, China
¹⁹ Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, Urumqi 830011, China
²⁰ Xinjiang Key Laboratory of Radio Astrophysics, Urumqi 830011, China
²¹ Haystack Observatory, Massachusetts Institute of Technology, 99 Millstone Road, Westford, MA 01886, USA
²² Chair of Remote Sensing Technology, School of Engineering and Design, Department of Aerospace and Geodesy, Technical University of Munich, Arcisstraße 21, 80333 Munich, Germany
²³ National Time Service Center, Chinese Academy of Sciences, Xi’An, Shaanxi 710600, China
²⁴ Key Laboratory of Time Reference and Applications, Chinese Academy of Sciences, China

^★ Corresponding authors; kyang2146@sjtu.edu.cn; yichen.zhang@sjtu.edu.cn; xinglu@shao.ac.cn

Received: 27 November 2024
Accepted: 31 December 2024

Abstract

The central molecular zone (CMZ) of our Galaxy exhibits widespread emission from SiO and various complex organic molecules (COMs), yet the exact origin of such emission is uncertain. Here we report the discovery of a unique class of long (>0.5 pc) and narrow (<0.03 pc) filaments in the emission of SiO 5–4 and eight additional molecular lines, including several COMs, in our ALMA 1.3 mm spectral line observations toward two massive molecular clouds in the CMZ, which we name as slim filaments. However, these filaments are not detected in the 1.3 mm continuum at the 5σ level. Their line-of-sight velocities are coherent and inconsistent with being outflows. The column densities and relative abundances of the detected molecules are statistically similar to those in protostellar outflows but different from those in dense cores within the same clouds. Turbulent pressure in these filaments dominates over self gravity and leads to hydrostatic inequilibrium, indicating that they are a different class of objects than the dense gas filaments in dynamical equilibrium ubiquitously found in nearby molecular clouds. We argue that these newly detected slim filaments are associated with parsec-scale shocks, likely arising from dynamic interactions between shock waves and molecular clouds. The dissipation of the slim filaments may replenish SiO and COMs in the interstellar medium and lead to their widespread emission in the CMZ.