HII regions and high-mass starless clump candidates II. Fragmentation
  and induced star formation at ~0.025 pc scale: An ALMA continuum study
  The ionization feedback from HII regions modifies the properties of high-mass
starless clumps (HMSCs, of several hundred to a few thousand solar masses with
a size of ~0.1-1 pc), such as temperature and turbulence, on the clump scale.
The question of whether the presence of HII regions modifies the core-scale
fragmentation and star formation in HMSCs remains to be explored. We aim to
investigate the difference of 0.025 pc-scale fragmentation between candidate
HMSCs that are strongly impacted by HII regions and less disturbed ones. We
also search for evidence of mass shaping and induced star formation in the
impacted HMSCs. Using the ALMA 1.3 mm continuum with a resolution of ~1.3", we
imaged eight candidate HMSCs, including four impacted by HII regions and
another four situated in the quiet environment. The less-impacted HMSCs are
selected on the basis of their similar mass and distance compared to the
impacted ones to avoid any possible bias linked to these parameters. A total of
51 cores were detected in eight clumps, with three to nine cores for each
clump. Within our limited sample, we did not find a clear difference in the
~0.025 pc-scale fragmentation between impacted and non-impacted HMSCs, even
though HII regions seem to affect the spatial distribution of the fragmented
cores. Both types of HMSCs present a thermal fragmentation with two-level
hierarchical features at the clump thermal Jeans length ${\lambda_{J,
clump}^{th}}$ and 0.3${\lambda_{J, clump}^{th}}$. The ALMA emission morphology
of the impacted HMSCs AGAL010.214-00.306 and AGAL018.931-00.029 sheds light on
the capacities of HII regions to shape gas and dust in their surroundings and
possibly to trigger star formation at ~0.025 pc-scale in HMSCs. Future ALMA
surveys covering a large number of impacted HMSCs with high turbulence are
needed to confirm the trend of fragmentation indicated in this study.
