HII regions and high-mass starless clump candidates I: Catalogs and
  properties
  The role of ionization feedback on high-mass (>8 Msun) star formation (HMSF)
is still highly debated. Questions remain concerning the presence of nearby HII
regions changes the properties of early HMSF and whether HII regions promote or
inhibit the formation of high-mass stars. To characterize the role of HII
regions on the HMSF, 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
HMSF; 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 nonassociated HMSCs based on statistical analyses of
multiwavelength data from infrared to radio. 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 HMSF due to the external heating
effects of the HII regions. 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.
