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Description
The role of ionization feedback on high-mass (>8M_{sun}_) star formation is still highly debated. Questions remain concerning the presence of nearby HII regions changes the properties of early high-mass star formation and whether H ii regions promote or inhibit the formation of high-mass stars. To characterize the role of HII regions on the formation of high-mass stars, we study the properties of a sample of candidates high-mass starless clumps (HMSCs), of which about 90% have masses larger than 100 Msun. These high-mass objects probably represent the earliest stages of high-mass star formation; we search if (and how) their properties are modified by the presence of an HII region. We took advantage of the recently published catalog of HMSC candidates. By cross matching the HMSCs and HII regions, we classified HMSCs into three categories: 1) The HMSCs associated with HII regions both in the position in the projected plane of the sky and in velocity; 2) HMSCs associated in the plane of the sky, but not in velocity; and 3) HMSCs far away from any HII regions in the projected sky plane. We carried out comparisons between associated and non-associated HMSCs based on statistical analyses of multiwavelength data from infrared to radio. We show that there are systematic differences of the properties of HMSCs in different environments. Statistical analyses suggest that HMSCs associated with HII regions are warmer, more luminous, more centrally-peaked and turbulent. We also clearly show, for the first time, that the ratio of bolometric luminosity to envelope mass of HMSCs (L/M) could not be a reliable evolutionary probe for early massive star formation due to the external heating effects of the HII regions. We show HMSCs associated with HII regions present statistically significant differences from HMSCs far away from HII regions, especially for dust temperature and L/M. More centrally peaked and turbulent properties of HMSCs associated with HII regions may promote the formation of high-mass stars by limiting fragmentation. High-resolution interferometric surveys toward HMSCs are crucial to reveal how HII regions impact the star formation process inside HMSCs.
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