H II regions as probes of galaxy evolution and the properties of massive stars

1993 ◽  
Vol 105 ◽  
pp. 996
Author(s):  
Donald R. Garnett
Keyword(s):  
Galaxy Evolution ◽  
Massive Stars ◽  
H Ii Regions

scholarly journals The Stellar Initial Mass Function in Starburst Galaxies

1999 ◽  
Vol 186 ◽  
pp. 243-250
Author(s):  
Claus Leitherer
Keyword(s):  
Massive Stars ◽  
Mass Function ◽  
Starburst Galaxies ◽  
Initial Mass Function ◽  
Initial Mass ◽  
H Ii Regions ◽  
Environmental Properties ◽  
Stellar Initial Mass Function ◽  
Low Mass ◽  
Star Formation Histories

Starburst galaxies are currently forming massive stars at prodigious rates. I discuss the star-formation histories and the shape of the initial mass function, with particular emphasis on the high- and on the low-mass end. The classical Salpeter IMF is consistent with constraints from observations of the most massive stars, irrespective of environmental properties. The situation at the low-mass end is less clear: direct star counts in nearby giant H II regions show stars down to ~1 M⊙, whereas dynamical arguments in some starburst galaxies suggest a deficit of such stars.

scholarly journals Simulated X-Ray Emission from Starburst Driven Winds

1998 ◽  
Vol 188 ◽  
pp. 287-288
Author(s):  
D. K. Strickland ◽  
I. R. Stevens ◽  
T. J. Ponman
Keyword(s):  
Galaxy Evolution ◽  
Massive Stars ◽  
Temperature Structure ◽  
Mass Loading ◽  
X Ray ◽  
Chemical Enrichment ◽  
Hot Gas ◽  
Galactic Winds ◽  
Complex Temperature ◽  
Initial Results

Winds from massive stars and supernovae in starburst galaxies drive global outflows of hot X-ray emitting plasma, as seen in M82 and NGC 253. These galactic winds are important for understanding galaxy evolution & formation, chemical enrichment of the IGM, and the starburst phenomenon itself.X-ray observations provide the only direct probe of the hot gas in these winds. However, the limitations of current X-ray observatories and factors such as complex temperature structure, mass loading by ambient material and projection effects all make the link between the observed data and existing 1 & 2-D modeling and theory difficult to make.We have therefore begun a program of numerical simulations of galactic winds, concentrating on predicting their observable X-ray properties. We present some initial results, comparing them to the archetypal starburst wind system M82.

scholarly journals HII regions and star formation in the Magellanic Clouds

1991 ◽  
Vol 148 ◽  
pp. 139-144 ◽  
Author(s):  
Robert C. Kennicutt
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Massive Star ◽  
Massive Stars ◽  
Hii Regions ◽  
Magellanic Clouds ◽  
H Ii Regions ◽  
Distant Galaxies ◽  
Close Range ◽  
Mass Functions

The H II regions in the Magellanic Clouds provide an opportunity to characterize the global star formation properties of a galaxy at close range. They also provide a unique laboratory for testing empirical tracers of the massive star formation rates and initial mass functions in more distant galaxies, and for studying the dynamical interactions between massive stars and the interstellar medium. This paper discusses several current studies in these areas.

scholarly journals When H ii regions are complicated: considering perturbations from winds, radiation pressure, and other effects

2019 ◽  
Vol 492 (1) ◽  
pp. 915-933 ◽  
Author(s):  
Sam Geen ◽  
Eric Pellegrini ◽  
Rebekka Bieri ◽  
Ralf Klessen
Keyword(s):  
Radiation Pressure ◽  
Large Range ◽  
Massive Stars ◽  
Relative Effect ◽  
H Ii Regions ◽  
Gas Temperature ◽  
Algebraic Models ◽  
Ionized Gas ◽  
Principal Mode ◽  
H Ii Region

ABSTRACT We explore to what extent simple algebraic models can be used to describe H ii regions when winds, radiation pressure, gravity, and photon breakout are included. We (a) develop algebraic models to describe the expansion of photoionized H ii regions under the influence of gravity and accretion in power-law density fields with ρ ∝ r−w, (b) determine when terms describing winds, radiation pressure, gravity, and photon breakout become significant enough to affect the dynamics of the H ii region where w = 2, and (c) solve these expressions for a set of physically motivated conditions. We find that photoionization feedback from massive stars is the principal mode of feedback on molecular cloud scales, driving accelerating outflows from molecular clouds in cases where the peaked density structure around young massive stars is considered at radii between ∼0.1 and 10–100 pc. Under a large range of conditions the effect of winds and radiation on the dynamics of H ii regions is around 10 per cent of the contribution from photoionization. The effect of winds and radiation pressure is most important at high densities, either close to the star or in very dense clouds such as those in the Central Molecular Zone of the Milky Way. Out to ∼0.1 pc they are the principal drivers of the H ii region. Lower metallicities make the relative effect of photoionization even stronger as the ionized gas temperature is higher.

Star formation at low rates: impact of lacking massive stars on the evolution of dwarf galaxies

2018 ◽  
Vol 14 (S344) ◽  
pp. 186-189
Author(s):  
P. Steyrleithner ◽  
G. Hensler ◽  
S. Recchi ◽  
S. Ploeckinger
Keyword(s):  
Star Formation ◽  
Numerical Simulations ◽  
Galaxy Evolution ◽  
Dwarf Galaxies ◽  
Massive Stars ◽  
Self Regulation ◽  
Mass Function ◽  
Initial Mass Function ◽  
Single Star ◽  
The Imf

AbstractIn recent years dedicated observations have uncovered star formation at extremely low rates in dwarf galaxies, tidal tails, ram-pressure stripped gas clouds, and the outskirts of galactic disks. At the same time, numerical simulations of galaxy evolution have advanced to higher spatial and mass resolutions, but have yet to account for the underfilling of the uppermost mass bins of stellar initial mass function (IMF) at low star-formation rates. In such situations, simulations may simply scale down the IMF, without realizing that this unrealistically results in fractions of massive stars, along with fractions of massive star feedback energy (e.g., radiation and SNII explosions). Not properly accounting for such parameters has consequences for the self-regulation of star formation, the energetics of galaxies, as well as for the evolution of chemical abundances. Here we present numerical simulations of dwarf galaxies with low star-formation rates allowing for two extreme cases of the IMF: a “filled” case with fractional massive stars vs. a truncated IMF, at which the IMF is built bottom-up until the gas reservoir allows the formation of a last single star at an uppermost mass. The aim of the study is to demonstrate the different effects on galaxy evolution with respect to self-regulation, feedback, and chemistry. The case of a stochastic sampled IMF is situated somewhere in between these extremes.

scholarly journals On the ionizing populations in GEHRs: unveiling integrated properties from the analysis of the Wolf-Rayet population

2003 ◽  
Vol 212 ◽  
pp. 698-699
Author(s):  
Marcelo Castellanos ◽  
Ángeles I. Díaz ◽  
Elena Terlevich
Keyword(s):  
Physical Properties ◽  
Emission Line ◽  
Massive Stars ◽  
Current Understanding ◽  
Evolutionary Synthesis ◽  
H Ii Regions ◽  
Expanding Atmospheres ◽  
Stars Evolution

In recent years, the detection of Wolf-Rayet stars in Giant Extragalactic H ii Regions (GEHRs) has yielded several questions about our current understanding of massive stars evolution and hot expanding atmospheres, the age of the ionizing populations and their impact onto the physical properties of GEHRs. Here, we present spectrophotometric observations of four extragalactic GEHRs which show WR features in their spectra. Our goal is to reproduce simultaneously the observed WR properties and the emission-line spectra with the help of current evolutionary synthesis models.

scholarly journals Structure and Fragmentation of Molecular Complexes

1987 ◽  
Vol 115 ◽  
pp. 443-444
Author(s):  
E. Falgarone ◽  
J. L. Puget ◽  
M. Pérault ◽  
S. Bonazzola ◽  
J. Heywaerts
Keyword(s):  
Hierarchical Model ◽  
Massive Stars ◽  
Molecular Complexes ◽  
H Ii Regions ◽  
Gravitational Stability

We propose a hierarchical model of large molecular complexes (mean density ∼ 10 cm−3, masses larger than 105 M⊙ relevant to their “cold phase”) which preceeds the formation of massive stars and H II regions, and investigate the gravitational stability of the different scales.

scholarly journals The growth of H ii regions around massive stars: the role of metallicity and dust

2020 ◽  
Author(s):  
Ahmad A Ali
Keyword(s):  
Star Formation ◽  
Radiation Pressure ◽  
Massive Stars ◽  
Particle Method ◽  
Diffuse Radiation ◽  
Uv Absorption ◽  
Expansion Velocity ◽  
H Ii Regions ◽  
Metal Line ◽  
Neutral Gas

Abstract Gas metallicity Z and the related dust-to-gas ratio fd can influence the growth of H ii regions via metal line cooling and UV absorption. We model these effects in star-forming regions containing massive stars. We compute stellar feedback from photoionization and radiation pressure (RP) using Monte Carlo radiative transfer coupled with hydrodynamics, including stellar and diffuse radiation fields. We follow a 105 M⊙ turbulent cloud with Z/Z⊙ = 2, 1, 0.5, 0.1 and fd = 0.01Z/Z⊙ with a cluster-sink particle method for star formation. The models evolve for at least 1.5Myr under feedback. Lower Z results in higher temperatures and therefore larger H ii regions. For Z ≥ Z⊙, radiation pressure Prad can dominate locally over the gas pressure Pgas in the inner half-parsec around sink particles. Globally, the ratio of Prad/Pgas is around 1 (2Z⊙), 0.3 (Z⊙), 0.1 (0.5Z⊙), and 0.03 (0.1Z⊙). In the solar model, excluding RP results in an ionized volume several times smaller than the fiducial model with both mechanisms. Excluding RP and UV attenuation by dust results in a larger ionized volume than the fiducial case. That is, UV absorption hinders growth more than RP helps it. The radial expansion velocity of ionized gas reaches +15km s−1 outwards, while neutral gas has inward velocities for most of the runtime, except for 0.1Z⊙ which exceeds +4km s−1. Z and fd do not significantly alter the star formation efficiency, rate, or cluster half-mass radius, with the exception of 0.1Z⊙ due to the earlier expulsion of neutral gas.

scholarly journals On the turbulence driving mode of expanding H ii regions

2020 ◽  
Vol 493 (4) ◽  
pp. 4643-4656 ◽  
Author(s):  
Shyam H Menon ◽  
Christoph Federrath ◽  
Rolf Kuiper
Keyword(s):  
Star Formation ◽  
Ionizing Radiation ◽  
Massive Stars ◽  
Parameter Analysis ◽  
Ionization Front ◽  
H Ii Regions ◽  
Driving Mode ◽  
Neutral Gas ◽  
Natural Mixture ◽  
Hydrodynamical Simulations

Abstract We investigate the turbulence driving mode of ionizing radiation from massive stars on the surrounding interstellar medium. We run hydrodynamical simulations of a turbulent cloud impinged by a plane-parallel ionization front. We find that the ionizing radiation forms pillars of neutral gas reminiscent of those seen in observations. We quantify the driving mode of the turbulence in the neutral gas by calculating the driving parameter b, which is characterized by the relation $\sigma _s^2 = \ln ({1+b^2\mathcal {M}^2})$ between the variance of the logarithmic density contrast $\sigma _s^2$ [where s = ln (ρ/ρ0) with the gas density ρ and its average ρ0], and the turbulent Mach number $\mathcal {M}$. Previous works have shown that b ∼ 1/3 indicates solenoidal (divergence-free) driving and b ∼ 1 indicates compressive (curl-free) driving, with b ∼ 1 producing up to ten times higher star formation rates than b ∼ 1/3. The time variation of b in our study allows us to infer that ionizing radiation is inherently a compressive turbulence driving source, with a time-averaged b ∼ 0.76 ± 0.08. We also investigate the value of b of the pillars, where star formation is expected to occur, and find that the pillars are characterized by a natural mixture of both solenoidal and compressive turbulent modes (b ∼ 0.4) when they form, and later evolve into a more compressive turbulent state with b ∼ 0.5–0.6. A virial parameter analysis of the pillar regions supports this conclusion. This indicates that ionizing radiation from massive stars may be able to trigger star formation by producing predominately compressive turbulent gas in the pillars.

scholarly journals The influence of massive stars on the interstellar medium

1999 ◽  
Vol 193 ◽  
pp. 627-635
Author(s):  
M. Sally Oey
Keyword(s):  
Galaxy Formation ◽  
Massive Stars ◽  
Stellar Winds ◽  
H Ii Regions ◽  
Feedback Effects ◽  
Star Forming ◽  
Galaxy Formation And Evolution ◽  
Formation And Evolution ◽  
The Relationship ◽  
Warm Ionized Medium

On scales ranging from pcs to kpcs, the relationship between stellar and gaseous galactic components forms the basis for interpreting observations of galaxies and understanding galaxy formation and evolution. Feedback effects from massive stars dominate the structure, ionization, kinematics, and enrichment of the gaseous ISM in star-forming galaxies. On galactic scales, the ionizing radiation from these stars creates populations of H II regions and the diffuse, warm ionized medium. Likewise, superbubbles created by stellar winds and supernovae strongly influence the structure, kinematics, and balance of the multiphase ISM. This contribution reviews these feedback effects of massive stars on the global ISM.

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