Molecular clouds and star formation toward the Galactic plane within 216.25° ≤l≤ 218.75° and −0.75° ≤b≤ 1.25°

Abstract

Context. Molecular clouds trace the spiral arms of the Milky Way and all its star forming regions. Large-scale mapping of molecular clouds will provide an approach to understand the processes that govern star formation and molecular cloud evolution. Aims. As a part of the Milky Way Imaging Scroll Painting (MWISP) survey, the aim is to study the physical properties of molecular clouds and their associated star formation toward the Galactic plane within 216.25• ≤ l ≤ 218.75• and −0.75• , which covers the molecular cloud complex S287. Methods. Using the 3 × 3 Superconducting Spectroscopic Array Receiver (SSAR) at the PMO-13.7m telescope, we performed a simultaneous 12 CO (1-0), 13 CO (1-0), C 18 O (1-0) mapping toward molecular clouds in a region encompassing 3.75 square degrees. We also make use of archival data to study star formation within the molecular clouds. Results. We reveal three molecular clouds, the 15 km s −1 cloud, the 27 km s −1 cloud, and the 50 km s −1 cloud, in the surveyed region. The 50 km s −1 cloud is resolved with an angular resolution of ∼1 for the first time. Investigating their morphology and velocity structures, we find that the 27 km s −1 cloud is likely affected by feedback from the stellar association Mon OB3 and the 50 km scloud is characterized by three large expanding molecular shells. The surveyed region is mapped in C 18 O (1-0) for the first time. We discover seven C 18 O clumps that are likely to form massive stars, and 15 dust clumps based on the Bolocam Galactic Plane Survey (BGPS) archive data. Using infrared color-color diagrams, we find 56 Class I and 107 Class II young stellar object (YSO) candidates toward a slightly larger region of 5.0 square degrees. Based on the distribution of YSO candidates, an overdensity is found around the HII region S287 and the intersection of two shells; this is probably indicative of triggering. The star formation efficiency (SFE) and rate (SFR) of the 27 km s −1 cloud are discussed. Comparing the observed values of the filament S287-main with fragmentation models, we suggest that turbulence controls the large-scale fragmentation in the filament, while gravitational fragmentation plays an important role in the formation of YSOs on small scales. We find that star-forming gas tends to have a higher excitation temperature, a higher 13 CO (1-0) opacity, and a higher column density than non-star-forming gas, which is consistent with the point that star formation occurs in denser gas and star-forming gas is heated by YSOs. Using the 1.1 mm dust emission to trace dense gas, we obtain a dense gas fraction of 2.7-10.4% for the 27 km s −1 cloud.Key words. surveys -ISM: clouds -stars: formation -radio lines: ISM -ISM: kinematics and dynamics IntroductionMolecular clouds are also known as stellar nurseries because they are the densest parts of the interstellar medium that may gravitationally collapse, and thus create protostars (e.g., Shu et al. 1987;Kennicutt & Evans 2012). Molecular clouds comprise a significant fraction of the total mass of in...

Molecular Cloud Distances Based on the MWISP CO Survey and Gaia DR2

“…In this section, we present our new procedure of calculating molecular cloud distances, as well as the results of applying it to the CO map of a chosen 100 deg 2 region containing 31 molecular clouds. Of the three CO isotopologue lines, 12 CO and 13 CO were well mapped, but the signal of C 18 O is too faint so it was only detected in S287 (see figure 10 of Gong et al 2016). Consequently, we only display the maps of 12 CO and 13 CO and ignore C 18 O, and for distance calculations, 12 CO maps alone are sufficient.…”

CO (J = 1–0) Observations toward Filamentary Molecular Clouds in the Galactic Region with l = [169.°75, 174.°75], b = [−0.°75, 0.°5]

“…Moreover, the filaments associated with more YSOs tend to have higher temperatures than the ones with fewer YSOs (e.g., EC-F(S) and EC-F(N), SC-F(N) and SC-F(S)). As pointed out by Gong et al (2016), the star-forming molecular gas tends to have a higher excitation temperature than the non-star-forming molecular gas. In our case, the existing YSOs could be the possible internal heating sources of the molecular gas with higher temperature.…”

A molecular absorption line survey towards the AGN of Hydra-A

“…The excitation temperatures are those derived from the HCO + (1-0) and HCO + (2-1) spectra. In the top plot, we show molecular clouds of the Milky Way observed at galactocentric radii of 4 -8 kpc (red pentagons, Roman-Duval et al 2010) and those in star forming regions toward the galactic plane (blue pentagons, Gong et al 2016).…”