The effects of ionization feedback on star formation: A case study of
  the M16 H II region
  We aim to investigate the impact of the ionized radiation from the M16 HII
region on the surrounding molecular cloud and on its hosted star formation. To
present comprehensive multi-wavelength observations towards the M16 HII region,
we used new CO data and existing infrared, optical, and submillimeter data. The
12CO J=1-0, 13CO J=1-0, and C18O J=1-0 data were obtained with the Purple
Mountain Observatory (PMO) 13.7m radio telescope. To trace massive clumps and
extract young stellar objects (YSOs) associated with the M16 HII region, we
used the ATLASGAL and GLIMPSE I catalogs, respectively. From CO data, we
discern a large-scale filament with three velocity components. Because these
three components overlap with each other in both velocity and space, the
filament may be made of three layers. The M16 ionized gas interacts with the
large-scale filament and has reshaped its structure. In the large-scale
filament, we find 51 compact cores from the ATLASGAL catalog, 20 of them being
quiescent. The mean excitation temperature of these cores is 22.5 K, while this
is 22.2 K for the quiescent cores. This high temperature observed for the
quiescent cores suggests that the cores may be heated by M16 and do not
experience internal heating from sources in the cores. Through the relationship
between the mass and radius of these cores, we obtain that 45% of all the cores
are massive enough to potentially form massive stars. Compared with the thermal
motion, the turbulence created by the nonthermal motion is responsible for the
core formation. For the pillars observed towards M16, the H II region may give
rise to the strong turbulence.
