Triggered massive and clustered stars formation by together H II regions
  G38.91-0.44 and G39.30-1.04
  We present the radio continuum, infrared, and CO molecular observations of
infrared dark cloud (IRDC) G38.95-0.47 and its adjacent H II regions
G38.91-0.44 (N74), G38.93-0.39 (N75), and G39.30-1.04. The Purple Mountain
Observation (PMO) 13.7 m radio telescope was used to detect12CO J=1-0,13CO
J=1-0 and C18O J=1-0 lines. The carbon monoxide (CO) molecular observations can
ensure the real association between the ionized gas and the neutral material
observed nearby. To select young stellar objects (YSOs) associated this region,
we used the GLIMPSE I catalog. The13CO J=1-0 emission presents two large cloud
clumps. The clump consistent with IRDC G38.95-0.47 shows a triangle- like
shape, and has a steep integrated-intensity gradient toward H II regions
G38.91-0.44 and G39.30-1.04, suggesting that the two H II regions have expanded
into the IRDC. Four submillmeter continuum sources have been detected in the
IRDC G38.95-0.47. Only the G038.95-00.47-M1 source with a mass of 117 Msun has
outflow and infall motions, indicating a newly forming massive star. We
detected a new collimated outflow in the clump compressed by G38.93-0.39. The
derived ages of the three H II regions are 6.1*10^5yr, 2.5*10^5yr, and
9.0*10^5yr, respectively. In the IRDC G38.95-0.47, the significant enhancement
of several Class I YSOs indicates the presence of some recently formed stars.
Comparing the ages of these H II regions with YSOs (Class I sources and massive
G038.95-00.47-M1 source), we suggest that YSOs may be triggered by G38.91-0.44
and G39.30-1.04 together, which supports the radiatively driven implosion
model. It may be the first time that the triggered star formation has occurred
in the IRDC compressed by two H II regions. The new detected outflow may be
driven by a star cluster.
