Star Formation Induced by Cloud-Cloud Collisions and Galactic Giant
  Molecular Cloud Evolution
  Recent radio observations towards nearby galaxies started to map the whole
disk and to identify giant molecular clouds (GMCs) even in the regions between
galactic spiral structures. Observed variations of GMC mass functions in
different galactic environment indicates that massive GMCs preferentially
reside along galactic spiral structures whereas inter-arm regions have many
small GMCs. Based on the phase transition dynamics from magnetized warm neutral
medium to molecular clouds, Kobayashi et al. 2017 proposes a semi-analytical
evolutionary description for GMC mass functions including cloud-cloud collision
(CCC) process. Their results show that CCC is less dominant in shaping the mass
function of GMCs compared with the accretion of dense HI gas driven by the
propagation of supersonic shock waves. However, their formulation does not take
into account the possible enhancement of star formation by CCC. Radio
observations within the Milky Way indicate the importance of CCC for the
formation of star clusters and massive stars. In this article, we reformulate
the time evolution equation largely modified from Kobayashi et al. 2017 so that
we additionally compute star formation subsequently taking place in CCC clouds.
Our results suggest that, although CCC events between smaller clouds outnumber
the ones between massive GMCs, CCC-driven star formation is mostly driven by
massive GMCs > 10^5.5 Msun (where Msun is the solar mass). The resultant
cumulative CCC-driven star formation may amount to a few 10 percent of the
total star formation in the Milky Way and nearby galaxies.
