Star-forming content of the giant molecular filaments in the Milky Way

¹ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: zhang@mpia.de
² Purple Mountain Observatory, and Key Laboratory for Radio Astronomy, Chinese Academy of Sciences, 210008 Nanjing, PR China
e-mail: miaomiao@pmo.ac.cn
³ Dept. of Space, Earth and Environment, Chalmers University of Technology Onsala Space Observatory, 439 92 Onsala, Sweden
⁴ Max-Planck-Institut für Radioastronomie (MPIfR), Auf dem Hügel 69, 53121 Bonn, Germany
⁵ Department of Astronomy, University of Arizona, 933 North Cherry Avenue, 85721 Tucson, AZ, USA

Received: 1 December 2017
Accepted: 2 November 2018

Abstract

Context. Through observations numerous giant molecular filaments (GMFs) have been discovered in the Milky Way. Their role in the Galactic star formation and Galaxy-scale evolution of dense gas is unknown.

Aims. We investigate systematically the star-forming content of all currently known GMFs. This allows us to estimate the star formation rates (SFRs) of the GMFs and to establish relationships between the SFRs and the GMF properties.

Methods. We identified and classified the young stellar object (YSO) population of each GMF using multiwavelength photometry from near- to far-infrared. We estimated the total SFRs assuming a universal and fully sampled initial mass function and luminosity function.

Results. We uniformly estimate the physical properties of 57 GMFs. The GMFs show correlations between the ¹³CO line width, mass, and size, similar to Larson’s relations. We identify 36 394 infrared excess sources in 57 GMFs and obtain SFRs for 46 GMFs. The median SFR surface density (Σ_SFR) and star formation efficiency (SFE) of GMFs are 0.62 M_⊙ Myr⁻¹ pc⁻² and 1%, similar to the nearby star-forming clouds. The star formation rate per free-fall time of GMFs is between 0.002−0.05 with the median value of 0.02. We also find a strong correlation between SFR and dense gas mass that is defined as gas mass above a visual extinction of 7 mag, which suggests that the SFRs of the GMFs scale similarly with dense gas as those of nearby molecular clouds. We also find a strong correlation between the mean SFR per unit length and dense gas mass per unit length. The origin of this scaling remains unknown, calling for further studies that can link the structure of GMFs to their SF activity and explore the differences between GMFs and other molecular clouds.