A Refined Sample of Lyman Excess H II Regions
  A large number (67) of the compact/ultra-compact H II regions identified in
the Coordinated Radio and Infrared Survey for High-Mass Star Formation
catalogue were determined to be powered by a Lyman continuum flux in excess of
what was expected given their corresponding luminosity. In this study we
attempt to reasonably explain the Lyman excess phenomenon in as many of the 67
H II regions as possible through a variety of observational and astrophysical
means including new luminosity estimates, new Herschel photometry, new distance
determinations, the use of different models for dust and ionized gas covering
factors, and the use of different stellar calibrations. This phenomenon has
been observed before; however, the objects shown to exhibit this behaviour in
the literature have decidedly different physical properties than the regions in
our sample, and thus the origin of the excess is not the same. We find that the
excess can be reproduced using OB stellar atmosphere models that have been
slightly modified in the extreme ultraviolet. Though the exact mechanism
producing the excess is still uncertain, we do find that a scaled up
magnetospheric accretion model, often used to explain similar emission from T
Tauri stars, is unable to match our observations. Our results suggest that the
Lyman excess may be associated with younger H II regions, and that it is more
commonly found in early B-type stars. Our refined sample of 24 Lyman excess H
II regions provides an ideal sample for comparative studies with regular H II
regions, and can act as the basis for the further detailed study of individual
regions.
