Related papers: HII region variability and pre-main-sequence evolu…

There has been considerable theoretical debate over whether photoionization and supernova feedback from the first Population III stars facilitate or suppress the formation of the next generation of stars. We present results from an Eulerian…

Gas metallicity $Z$ and the related dust-to-gas ratio $f_\textrm{d}$ can influence the growth of HII regions via metal line cooling and UV absorption. We model these effects in star-forming regions containing massive stars. We compute…

We summarize the status of our program of near-infrared adaptive optics observations of ultracompact HII regions. By means of selected results we demonstrate the usefulness of this technique for disentangling the complexity of massive…

In general, HII regions do not show clear signs of self-enrichment in products from massive stars (M > 8 M_sun). In order to explore why, I modeled the contamination with Wolf-Rayet star ejecta of metal-poor (Z=0.001) HII regions, ionised…

Magnetic fields permeate the Universe on all scales and play a key role during star formation. We study the evolution of magnetic fields around a massive metal-free (Population III) star at $z \sim 15$ during the growth of its HII region…

We have computed a series of realistic and self-consistent models that have been shown to be able to reproduce the emitted spectra of HII galaxies in a star bursting scenario (Martin-Majon et al. 2008). Our models combine different codes of…

Accretion flows onto massive stars must transfer mass so quickly that they are themselves gravitationally unstable, forming dense clumps and filaments. These density perturbations interact with young massive stars, emitting ionizing…

We present semi-analytic dynamical models for giant molecular clouds evolving under the influence of HII regions launched by newborn star clusters. In contrast to previous work, we neither assume that clouds are in virial or energetic…

It is a challenge to study the formation process of massive stars: their formation time is short, they are few, often deeply embedded, and at relatively large distances. Our strategy is to study the outcome of the star formation process and…

Ionization fronts, the sharp radiation fronts behind which H/He ionizing photons from massive stars and galaxies propagate through space, were ubiquitous in the universe from its earliest times. The cosmic dark ages ended with the formation…

We investigate the size--density relation in extragalactic HII regions, with the aim of understanding the role of dust and different physical conditions in the ionized medium. First, we compiled several observational data sets for Galactic…

Cosmic reionization progresses as HII regions form around sources of ionizing radiation. Their average size grows continuously until they percolate and complete reionization. We demonstrate how this typical growth can be calculated around…

We present general properties of ionized hydrogen (HII) bubbles and their growth based on a state-of-the-art large-scale (100 Mpc/h) cosmological radiative transfer simulation. The simulation resolves all halos with atomic cooling at the…

We present a detailed study of the massive star-forming region G35.2-0.74N with ALMA 1.3 mm multi-configuration observations. At 0.2" (440 au) resolution, the continuum emission reveals several dense cores along a filamentary structure,…

High mass proto-stars create Ultra-Compact Hii regions (UCHII) at the stage of evolution when most of the accretion is finished but the star is still heavily embedded in molecular material. The morphologies of UCHII regions reflect the…

Connecting the gas in HII regions to the underlying source of the ionizing radiation can help us constrain the physical processes of stellar feedback and how HII regions evolve over time. With PHANGS$\unicode{x2013}$MUSE we detect nearly…

We present an analysis of multi-wavelength observations of an area of 0.27 deg x 0.27 deg around the Galactic HII region G18.88-0.49, which is powered by an O-type star (age ~10^5 years). The Herschel column density map reveals a shell-like…

We present Australia Telescope Compact Array observations towards 6 massive star formation regions which, from their strong 24 GHz continuum emission but no compact 8 GHz continuum emission, appeared good candidates for hyper-compact HII…

We study the structural evolution of turbulent molecular clouds under the influence of ionizing radiation emitted from a nearby massive star by performing a high resolution parameter study with the iVINE code. The temperature is taken to be…

We use cosmological simulations of reionization to predict the effect of large HII regions around individual high-redshift quasars on the possible signal from the redshifted 21cm line of neutral hydrogen in the pre-reionization era. We show…