2019ApJ...880...88X

We present observations of the CO isotopologues (¹²CO, ¹³CO, and C¹⁸O) toward the Galactic region with 169.°75 <= l <= 174.°75 and -0.°75 <= b <= 0.°5 using the Purple Mountain Observatory 13.7 m millimeter-wavelength telescope. Based on the ¹³CO (J = 1 - 0) data, we find five molecular clouds within the velocity range between -25 and 8 km s^–1 that are all characterized by conspicuous filamentary structures. We have identified eight filaments with a length of 6.38-28.45 pc, a mean H₂ column density of 0.70 x 10²¹-6.53 x 10²¹ cm^–2, and a line mass of 20.24-161.91 M_☉ pc^–1, assuming a distance of ∼1.7 kpc. Gaussian fittings to the inner parts of the radial density profiles lead to a mean FWHM width of 1.13 ± 0.01 pc. The velocity structures of most filaments present continuous distributions with slight velocity gradients. We find that turbulence is the dominant internal pressure to support the fragmentation of filaments instead of thermal pressure. Most filaments have virial parameters smaller than 2; thus, they are gravitationally bound. Four filaments have an LTE line mass close to the virial line mass. We further extract dense clumps using the ¹³CO data and find that 64% of the clumps are associated with the filaments. According to the complementary IR data, most filaments have associated Class II young stellar objects. Class I objects are mainly found to be located in the filaments with a virial parameter close to 1. Within two virialized filaments, ¹²CO outflows have been detected, indicating ongoing star-forming activity therein.