Title: Star Formation Activity in the molecular cloud G35.20$-$0.74: onset of cloud-cloud collision,
Abstract: To probe the star-formation (SF) processes, we present results of an analysis
of the molecular cloud G35.20$-$0.74 (hereafter MCG35.2) using multi-frequency
observations. The MCG35.2 is depicted in a velocity range of 30-40 km s$^{-1}$.
An almost horseshoe-like structure embedded within the MCG35.2 is evident in
the infrared and millimeter images and harbors the previously known sites,
ultra-compact/hyper-compact G35.20$-$0.74N H\,{\sc ii} region, Ap2-1, and
Mercer 14 at its base. The site, Ap2-1 is found to be excited by a radio
spectral type of B0.5V star where the distribution of 20 cm and H$\alpha$
emission is surrounded by the extended molecular hydrogen emission. Using the
{\it Herschel} 160-500 $\mu$m and photometric 1-24 $\mu$m data analysis,
several embedded clumps and clusters of young stellar objects (YSOs) are
investigated within the MCG35.2, revealing the SF activities. Majority of the
YSOs clusters and massive clumps (500-4250 M$_{\odot}$) are seen toward the
horseshoe-like structure. The position-velocity analysis of $^{13}$CO emission
shows a blue-shifted peak (at 33 km s$^{-1}$) and a red-shifted peak (at 37 km
s$^{-1}$) interconnected by lower intensity intermediated velocity emission,
tracing a broad bridge feature. The presence of such broad bridge feature
suggests the onset of a collision between molecular components in the MCG35.2.
A noticeable change in the H-band starlight mean polarization angles has also
been observed in the MCG35.2, probably tracing the interaction between
molecular components. Taken together, it seems that the cloud-cloud collision
process has influenced the birth of massive stars and YSOs clusters in the
MCG35.2.