Cluster formation in the W40 and Serpens South complex triggered by the
  expanding HII region
  We present results of the mapping observations covering a large area of 1
square degree around W40 and Serpens South carried out in the 12CO (J=1-0),
13CO (J=1-0), C18O (J=1-0), CCS (J_{N}=8_{7}-7_{6}), and N_2H+ (J=1-0) emission
lines with the 45 m Nobeyama Radio Telescope. W40 is a blistered Hii region,
and Serpens South is an infrared dark cloud accompanied by a young cluster. The
relationship between these two regions which are separated by ~20' on the sky
has not been clear so far. We found that the C18O emission is distributed
smoothly throughout the W40 and Serpens South regions, and it seems that the
two regions are physically connected. We divided the C18O emission into four
groups in terms of the spatial distributions around the HII region which we
call 5, 6, 7, and 8 km s^{-1} components according to their typical LSR
velocities, and propose a three-dimensional model of the W40 and Serpens South
complex. We found two elliptical structures in position-velocity diagrams,
which can be explained as a part of two expanding shells. One of the shells is
the small inner shell just around the HII region, and the other is the large
outer shell corresponding to the boundary of the HII region. Dense gas
associated with the young cluster of Serpens South is likely to be located at
the surface of the outer shell, indicating that the natal clump of the young
cluster is interacting with the outer shell being compressed by the expansion
of the shell. We suggest that the expansion of the shell induced the formation
of the young cluster.
