The impact of expanding HII regions on filament G37

Curved magnetic field and multiple direction material flows

¹ School of Astronomy and Space Science, Nanjing University, 163 Xianlin Avenue, Nanjing 210023, PR China
² Xinjiang Astronomical Observatory, Chinese Academy of Sciences, Urumqi 830011, PR China
³ University of Chinese Academy of Sciences, Beijing 100049, PR China
⁴ Key Laboratory of Radio Astronomy and Technology (Chinese Academy of Sciences), A20 Datun Road, Chaoyang District, Beijing 100101, PR China
⁵ Xinjiang Key Laboratory of Radio Astrophysics, Urumqi 830011, PR China
⁶ Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education, Nanjing 210023, Jiangsu, PR China

^★ Corresponding authors: mkzhao628@gmail.com; tangxindi@xao.ac.cn

Received: 3 June 2024
Accepted: 28 February 2025

Abstract

Filament G37 exhibits a distinctive “caterpillar” shape, characterized by two semicircular structures within its 40 pc-long body, and provides an ideal target to investigate the formation and evolution of filaments. By analyzing multiple observational data, such as the CO spectral line, the Hα radio recombination line, and the multiwavelength continuum, we find that the expanding H II regions that surround filament G37 exert pressure on the structure of the filament body, which kinetic process present as the gas flows in multiple directions along the skeleton of the filament body. The curved magnetic field structure of filament G37 derived by employing the velocity gradient technique with CO is found to be parallel to the filament body and support the pressure from expanded H II regions. The multidirectional flows in filament G37 could cause the accumulation and subsequent collapse of gas, which would result in the formation of massive clumps. The curved structure and star formation observed in filament G37 are likely to be a result of the filament body being squeezed by the expanding H II region. This physical process occurs over a timescale of approximately 5 Myr. Filament G37 provides a potential candidate for end-dominated collapse.