Unveiling molecular clouds toward bipolar HII region G8.14+0.23
  Most recent numerical simulations suggest that bipolar HII regions, powered
by O-type stars, can be formed at the interface of two colliding clouds. To
observationally understand the birth of O-type stars, we present a detailed
multi-wavelength analysis of an area of 1 deg x 1 deg hosting G8.14+0.23 HII
region associated with an infrared bipolar nebula (BPN). Based on the radio
continuum map, the HII region is excited by at least an O-type star, which is
located toward the waist of the BPN. The NANTEN2 13CO line data reveal the
existence of two extended clouds at [9, 14.3] and [15.3, 23.3] km/s toward the
site G8.14+0.23, which are connected in the position-velocity space through a
broad-bridge feature at the intermediate velocity range. A
"cavity/intensity-depression" feature is evident in the blueshifted cloud, and
is spatially matched by the "elongated redshifted cloud". The spatial and
velocity connections of the clouds suggest their interaction in the site
G8.14+0.23. The analysis of deep near-infrared photometric data reveals the
presence of clusters of infrared-excess sources, illustrating ongoing star
formation activities in both the clouds. The O-type star is part of the
embedded cluster seen in the waist of the BPN, which is observed toward the
spatial matching zone of the cavity and the redshifted cloud. The observational
results appear to be in reasonable agreement with the numerical simulations of
cloud-cloud collision (CCC), suggesting that the CCC process seems to be
responsible for the birth of the O-type star in G8.14+0.23.
