2021A&A...646A..25Z

Context. 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 typical size of 0.1-1pc), such as dust temperature and turbulence, on the clump scale. The question of whether the presence of HII regions modifies the core-scale (∼0.025pc) fragmentation and star formation in HMSCs remains to be explored.
Aims. We aim to investigate the difference of 0.025pc-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 candidate HMSCs.
Methods. Using the ALMA 1.3 mm continuum, with a typical angular 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 candidate 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. We carried out a comparison between the two types of candidate HMSCs. We used multi-wavelength data to analyze the interaction between HII regions and the impacted candidate HMSCs.
Results. 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 ∼0.025pc-scale fragmentation between impacted and non-impacted candidate HMSCs, even though HII regions seem to affect the spatial distribution of the fragmented cores. Both types of candidate HMSCs present a thermal fragmentation with two-level hierarchical features at the clump thermal Jeans length λ_J,clump^th and 0.3λ_J,clump^th. The ALMA emission morphology of the impacted candidate 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 ∼0.025pc-scale in candidate HMSCs.
Conclusions. The fragmentation at ∼0.025pc scale for both types of candidate HMSCs is likely to be thermal-dominant, meanwhile HII regions probably have the capacity to assist in the formation of dense structures in the impacted candidate HMSCs. Future ALMA imaging surveys covering a large number of impacted candidate HMSCs with high turbulence levels are needed to confirm the trend of fragmentation indicated in this study.