Related papers: Hydrodynamical models of cometary HII regions
We present numerical radiation-hydrodynamic simulations of the evolution of HII regions formed in an inhomogeneous medium resulting from turbulence simulations. We find that the filamentary structure of the underlying density distribution…
The slow and dense wind from a symbiotic red giant can be significantly deflected toward the orbital plane by the gravitational pull of the companion star. In such an environment, the ionizing radiation from the companion creates a highly…
We present the first detailed study of the large, ~30 pc diameter, inner-Galaxy HII region W 39. Radio recombination line observations combined with HI absorption spectra and Galactic rotation models show that the region lies at V(LSR) =…
We report the detection of ongoing star formation in the prominent tidal arms near NGC 3077 (member of the M 81 triplet). In total, 36 faint compact HII regions were identified, covering an area of ~4x6 kpc^2. Most of the HII regions are…
A number of very small isolated HII regions have been discovered at projected distances up to 30 kpc from their nearest galaxy. These HII regions appear as tiny emission line objects in narrow band images obtained by the NOAO Survey for…
HII regions in the arms of spiral galaxies are indicators of recent star-forming processes. They may have been caused by the passage of the density wave or simply created by other means near the arms. The study of these regions may give us…
At least 25 per cent of massive stars are ejected from their parent cluster, becoming runaways or exiles, travelling with often-supersonic space velocities through the interstellar medium (ISM). Their overpressurised H II regions impart…
Massive stars and their associated ionized (HII) regions could play a key role in the formation and evolution of filaments that host star formation. However, the properties of filaments that interact with H regions are still poorly known.…
Radiation pressure acting on gas and dust causes HII regions to have central densities that are lower than the density near the ionized boundary. HII regions in static equilibrium comprise a family of similarity solutions, parametrized by 3…
We review the phenomenon of ultra-compact H II regions (UCHIIs) as a key phase in the early lives of massive stars. This most visible manifestation of massive star formation begins when the Lyman continuum output from the massive young…
Star formation in relic HII regions of the first stars is investigated using magneto-hydrodynamical simulations with a nested grid method that covers 10 orders of magnitude in spatial scale and 20 orders of magnitude in density contrast.…
The luminosities, colors and H\alpha\ emission for 429 HII regions in 54 LSB galaxies are presented. While the number of HII regions per galaxy is lower in LSB galaxies compared to star-forming irregulars and spirals, there is no indication…
The spatial morphology, spectral characteristics, and time variability of ultracompact H II regions provide strong constraints on the process of massive star formation. We have performed simulations of the gravitational collapse of rotating…
Aims: NGC 1530 has one of the strongest bars ever observed and recent star formation sites are distributed across its bar. Our aim is to study the photometric properties of the bar and its HII regions, to elucidate the conditions under…
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…
Velocity shifts and differential broadening of radio recombination lines are used to estimate the densities and velocities of the ionized gas in several hypercompact and ultracompact HII regions. These small HII regions are thought to be at…
We constructed diagnostic diagrams using emission line ratios and equivalent widths observed in several samples of HII galaxies. The diagrams are compared to predictions from new photoionization models for evolving starbursts. We find that…
Mid-infrared arcs of dust emission are often seen near ionizing stars within HII regions. A possible explanations for these arcs is that they could show the outer edges of asymmetric stellar wind bubbles. We use two-dimensional,…
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 a new observation of the compact HII region, G29.96-0.02, that allows us to compare the velocity structure in the ionised gas and surrounding molecular gas directly. This allows us to remove most of the remaining ambiguity about…