CESARONI, RiccardoRiccardoCESARONISánchez-Monge, Á.Á.Sánchez-MongeBELTRAN SOROLLA, MARIA TERESAMARIA TERESABELTRAN SOROLLAMOLINARI, SergioSergioMOLINARIOLMI, LUCALUCAOLMITreviño-Morales, S. P.S. P.Treviño-Morales2020-05-052020-05-0520160004-6361http://hdl.handle.net/20.500.12386/24512Context. Ionized regions around early-type stars are believed to be well-known objects, but until recently, our knowledge of the relation between the free-free radio emission and the IR emission has been observationally hindered by the limited angular resolution in the far-IR. The advent of Herschel has now made it possible to obtain a more precise comparison between the two regimes, and it has been found that about a third of the young H II regions emit more Lyman continuum photons than expected, thus presenting a Lyman excess. Aims: With the present study we wish to distinguish between two scenarios that have been proposed to explain the existence of the Lyman excess: (I) underestimation of the bolometric luminosity, or (II) additional emission of Lyman-continuum photons from an accretion shock. Methods: We observed an outflow (SiO) and an infall (HCO<SUP>+</SUP>) tracer toward a complete sample of 200 H II regions, 67 of which present the Lyman excess. Our goal was to search for any systematic difference between sources with Lyman excess and those without. Results: While the outflow tracer does not reveal any significant difference between the two subsamples of H II regions, the infall tracer indicates that the Lyman-excess sources are more associated with infall signposts than the other objects. Conclusions: Our findings indicate that the most plausible explanation for the Lyman excess is that in addition to the Lyman continuum emission from the early-type star, UV photons are emitted from accretion shocks in the stellar neighborhood. This result suggests that high-mass stars and/or stellar clusters containing young massive stars may continue to accrete for a long time, even after the development of a compact H II region. Based on observations carried out with the IRAM 30 m Telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).ELETTRONICOenArticle10.1051/0004-6361/2015278412-s2.0-84961777971000373207800008https://www.aanda.org/articles/aa/abs/2016/04/aa27841-15/aa27841-15.html2016A&A...588L...5CFIS/05 - ASTRONOMIA E ASTROFISICA