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The HII region W3 is one of the most outstanding regions of high-mass star formation. Based on a new analysis of the $^{12}$CO($J$ = 2-1) data obtained at 38$$ resolution, we have found that each of the two active regions of high-mass star formation, W3 Main and W3(OH), is associated with two clouds of different velocities separated by 3-4 km s$^{-1}$, having cloud mass of 2000-4000 $M_odot$ in each. In the two regions we have found typical signatures of a cloud-cloud collision, i.e.,the complementary distribution with/without a displacement between the two clouds and/or a V-shape in the position-velocity diagram. We frame a hypothesis that a cloud-cloud collision triggered the high-mass star formation in the two regions. The collision in W3 Main involves a small cloud of $sim$5 pc in diameter which collided with a large cloud of 10 pc $times$ 20 pc. The collision in W3 Main compressed the gas in the direction of the collision path toward the west over a timescale of $sim$1 Myr, where the dense gas W3 core associated with ten O stars are formed. The collision also produced a cavity in the large cloud having a size similar to the small cloud. The collision in W3(OH) has a younger timescale of $sim$0.5 Myr and the forming-star candidates are heavily embedded in the clouds. The results reinforce the idea that a cloud-cloud collision is an essential process in high-mass star formation by rapidly creating the initial condition of 1 g cm$^{-2}$ in the natal gas.
We present a multi-wavelength analysis of the history of star formation in the W3 complex. Using deep, near-infrared ground-based images, combined with images obtained with Spitzer and Chandra observatories, we identified and classified young embedde
We present near-infrared JHKs imaging as well as K-band multi-object spectroscopy of the massive stellar content of W3 Main using LUCI at the LBT. We confirm 13 OB stars by their absorption line spectra in W3 Main and spectral types between O5V and B
In order to study a molecular-cloud-scale chemical composition, we have conducted a mapping spectral line survey toward the Galactic molecular cloud W3(OH), which is one of the most active star forming regions in the Perseus arm, with the NRO 45 m te
We observed three high-mass star-forming regions in the W3 high-mass star formation complex with the Submillimeter Array and IRAM 30 m telescope. These regions, i.e. W3 SMS1 (W3 IRS5), SMS2 (W3 IRS4) and SMS3, are in different evolutionary stages and
We report the first evidence for high-mass star formation triggered by collisions of molecular clouds in M33. Using the Atacama Large Millimeter/submillimeter Array, we spatially resolved filamentary structures of giant molecular cloud 37 in M33 usin