Theoretical models of high-mass star formation lie between two extreme scenarios. At one extreme, all the mass comes from an initially gravitationally bound core. At the other extreme, the majority of the mass comes from cluster scale gas, which lies far outside the initial core boundary. One way to unambiguously show high-mass stars can assemble their gas through the former route would be to find a high-mass star forming in isolation. Making use of recently available CORNISH and ATLASGAL Galactic plane survey data, we develop sample selection criteria to try and find such an object. From an initial list of approximately 200 sources, we identify the high-mass star-forming region G13.384 + 0.064 as the most promising candidate. The region contains a strong radio continuum source, that is powered by an early B-type star. The bolometric luminosity, derived from infrared measurements, is consistent with this. However, sub-millimetre continuum emission, measured in ATLASGAL, as well as dense gas tracers, such as HCO+(3–2) and N2H+(3–2) indicate that there is less than ~ 100 M⊙ of material surrounding this star. We conclude that this region is indeed a promising candidate for a high-mass star forming in isolation.

The combination of stellar population synthesis models and photoionization models allows a better understanding of the spectral features of HII regions and HII galaxies. In this work we show that sampling effects in the initial mass function (IMF) are very important in the low cluster mass case. To this aim, we compute photoionization models ionized by realistic clusters made up of various combinations of individual stars and clusters made up with a synthesis model. We discuss the differences in the position on diagnostic diagrams and their implications.

We present results from our ongoing survey of Galactic Giant HII Regions in the near-infrared. The luminosity function indicates that the IMF is uniform, independent of the galactocentric distance and compatible with Salpeter (1955) slope. Distances measured by the spectroscopic parallax method are systematically smaller than kinematic distances derived from radio techniques. As a consequence, the number of ionizing photons and the star formation rate is much lower than that derived from rotation models. Although the luminosities of the giant HII regions obtained from this method are lower than by other methods, the morphological type of the Milky Way is well in line of previous results, close to Sbc or Sc types.