New insights in the mid-infrared bubble N49 site: a clue of collision of
  filamentary molecular clouds
  We investigate the star formation processes operating in a mid-infrared
bubble N49 site, which harbors an O-type star in its interior, an ultracompact
HII region, and a 6.7 GHz methanol maser at its edges. The 13CO line data
reveal two velocity components (at velocity peaks ~88 and ~95 km/sec) in the
direction of the bubble. An elongated filamentary feature (length >15 pc) is
investigated in each molecular cloud component, and the bubble is found at the
interface of these two filamentary molecular clouds. The Herschel temperature
map traces all these structures in a temperature range of ~16-24 K. In the
velocity space of 13CO, the two molecular clouds are separated by ~7 km/sec,
and are interconnected by a lower intensity intermediate velocity emission
(i.e. a broad bridge feature). A possible complementary molecular pair at [87,
88] km/sec and [95, 96] km/sec is also observed in the velocity channel maps.
These observational signatures are in agreement with the outcomes of
simulations of the cloud-cloud collision process. There are also noticeable
embedded protostars and Herschel clumps distributed toward the filamentary
features including the intersection zone of the two molecular clouds. In the
bubble site, different early evolutionary stages of massive star formation are
also present. Together, these observational results suggest that in the bubble
N49 site, the collision of the filamentary molecular clouds appears to be
operated about 0.7 Myr ago, and may have triggered the formation of embedded
protostars and massive stars.
