Star burst in W 49 N presumably induced by cloud–cloud collision

We present high resolution observations of CS(J=1-0), H13CO+ (J=1-0), and SiO(v=0:J=1-0) lines, together with the 49GHz 86GHz continuum emissions, toward W49N carried out Nobeyama Millimeter Array. identified 11 CS, 8 H13CO+, 6 SiO clumps radii 0.1-0.5pc. The CS are mainly divided into two velocity components, one at 4kms-1 other 12kms-1, while have velocities between components. emission is distributed UCHII ring, where component also exist. 12kms-1 detected east west ring an apparent hole ring. clump masses vary from 4.4x10^2 M_SUN to 4.9x10^4 mean values 0.94x10^4M_SUN, 0.88x10^4M_SUN, 2.2x10^4M_SUN for clumps, respectively. total derived 1.0x10^5M_SUN, 0.70x10^5M_SUN, 1.3x10^5 M_SUN, respectively, which agree well corresponding virial 0.71x10^5M_SUN, 1.3x10^5M_SUN, 0.88x10^5M_SUN, average molecular hydrogen densities 0.90x10^6 cm-3, 1.4x10^6cm-3, 7.6x10^6 cm-3 density seems significantly higher than those others, probably because produced in shocked regions. free fall time scale estimated be ~3x10^4 yr, gives accretion rate 3x10-3-1M_SUN yr-1 onto a stellar core. observed are, if they undergoing fall, capable producing dozens massive stars next 10^5 yr. propose view that pre-existing clouds collided each almost face-on produce triggered burst star formation W49N.