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 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.

scholarly journals Stellar feedback from a massive Super Star Cluster in the Antennae merger

2015 ◽  
Vol 12 (S316) ◽  
pp. 190-195 ◽  
Author(s):  
Cinthya N. Herrera ◽  
Francois Boulanger
Keyword(s):  
Star Formation ◽  
Radiation Pressure ◽  
Angular Resolution ◽  
Massive Stars ◽  
Star Cluster ◽  
Molecular Gas ◽  
Structure And Dynamics ◽  
Stellar Feedback ◽  
Formation Efficiency ◽  
Co Gas

AbstractStellar feedback from massive stars can unbind and disperse large amount of molecular gas, affecting the star formation efficiency. Based on ALMA and VLT observations in the Antennae galaxies we study a massive (~ 107 M⊙) and young (~ 3 Myr) SSC, B1, associated with compact molecular and ionized emission, which suggests that it is embedded in its parent cloud. However, we found contradictories and puzzling results on the structure and dynamics of the matter around the cluster, indicating that SSC B1 is not embedded in its parent cloud after all. We propose that radiation pressure was highly enhanced at the early stages of the SSC formation, disrupting the parent cloud in < 3 Myr. We show evidences of outflowing gas from the parent cloud in the more extended CO gas. Higher angular resolution observations are needed to validate this interpretation and to understand the origin and fate of the component seen to be associated with SSC B1.

scholarly journals Gas and Dust in M33

2010 ◽  
Vol 6 (S277) ◽  
pp. 63-66 ◽  
Author(s):  
J. Braine ◽  
P. Gratier ◽  
C. Kramer ◽  
B. Mookerjea ◽  
M. Xilouris ◽  
...  
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Luminosity Function ◽  
Massive Stars ◽  
Dust Emission ◽  
Emission Lines ◽  
Neutral Gas ◽  
Dust Temperature ◽  
Near Future ◽  
Co Emission

AbstractWe present results from the Herschel and IRAM projects to map M33 in the dust continuum and main emission lines, particularly C[II] and CO. The temperature of the cool dust decreases with distance from the center of M33 from ~25K to ~13K. The CO emission generally follows the dust temperature and the overall dust emission. However, about 1/6 of the molecular clouds are not associated with massive stars, such that about 1/6th the lifetime of an entity identifiable as a molecular cloud is in a pre-star formation state. These clouds are less CO-bright than those with massive stars. The largest sample of molecular clouds currently available for an external galaxy shows that the cloud CO luminosity function, usually viewed as the cloud H2 mass, steepens with radius such that smaller clouds are more numerous in the outer parts. The observations of the C[II] line with Herschel indicate that the C[II] emission traces on-going star formation rather than the neutral gas. This identification will be tested via velocity-resolved Herschel/HIFI C[II] spectra in the near future.

scholarly journals Starbursting [O iii] emitters and quiescent [C ii] emitters in the reionization era

2020 ◽  
Vol 498 (4) ◽  
pp. 5541-5556 ◽  
Author(s):  
Shohei Arata ◽  
Hidenobu Yajima ◽  
Kentaro Nagamine ◽  
Makito Abe ◽  
Sadegh Khochfar
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Line Emission ◽  
Abundance Ratio ◽  
Relative Distribution ◽  
Metal Line ◽  
Hydrodynamic Simulations ◽  
Neutral Gas ◽  
Solar Metallicity ◽  
Supernova Feedback

ABSTRACT Recent observations have successfully detected [O iii] $88.3\, {\rm \mu m}$ and [C ii] $157.6\, {\rm \mu m}$ lines from galaxies in the early Universe with the Atacama Large Millimeter Array. Combining cosmological hydrodynamic simulations and radiative transfer calculations, we present relations between the metal line emission and galaxy evolution at z = 6–15. We find that galaxies during their starburst phases have high [O iii] luminosity of ${\sim}10^{42}~\rm erg~s^{-1}$. Once supernova feedback quenches star formation, [O iii] luminosities rapidly decrease and continue to be zero for ${\sim}100\, {\rm Myr}$. The slope of the relation between $\log {(\rm SFR/\rm M_{\odot }~ yr^{-1})}$ and $\log {(L_{\rm [O\, \small {III}]}/\mathrm{L}_{\odot })}$ at z = 6–9 is 1.03, and 1.43 for $\log {(L_{\rm [C\, \small {II}]}/\mathrm{L}_{\odot })}$. As gas metallicity increases from sub-solar to solar metallicity by metal enrichment from star formation and feedback, the line luminosity ratio $L_{\rm [O\, \small {III}]} / L_{\rm [C\, \small {II}]}$ decreases from ∼10 to ∼1 because the O/C abundance ratio decreases due to carbon-rich winds from AGB stars and the mass ratio of H ii to H i regions decreases due to rapid recombination. Therefore, we suggest that the combination of [O iii] and [C ii] lines is a good probe to investigate the relative distribution of ionized and neutral gas in high-z galaxies. In addition, we show that deep [C ii] observations with a sensitivity of ∼10−2 mJy arcsec−2 can probe the extended neutral gas discs of high-z galaxies.

scholarly journals A Study of Dense Molecular Gas and Star Formation toward the Vela Molecular Ridge with NANTEN

1999 ◽  
Vol 51 (6) ◽  
pp. 775-790 ◽  
Author(s):  
Nobuyuki Yamaguchi ◽  
Norikazu Mizuno ◽  
Hiro Saito ◽  
Ken'ichi Matsunaga ◽  
Akira Mizuno ◽  
...  
Keyword(s):  
Star Formation ◽  
Total Mass ◽  
Massive Stars ◽  
Emission Lines ◽  
Molecular Gas ◽  
H Ii Regions ◽  
Molecular Outflow ◽  
Total Luminosity ◽  
Preceding Work ◽  
Order Of Magnitude

Abstract New observations of the J=1−0 12CO, 13CO, and C18O emission lines have been extensively made toward the Vela Molecular Ridge (VMR) with NANTEN. The most prominent cloud is the giant molecular cloud, corresponding to the VMR-C region (Vela C). The present C18O distribution has been identified as 29 clouds. Among them, the most massive one is included in Vela C, having a total mass of ∼ 4.4 × 104M⊙. The rest of them are smaller C18O clouds of 102-103M⊙. Star formation in the region is almost exclusively occurring in the C18O clouds. The luminosities of the associated protostellar IRAS sources range from 5 L⊙ to 1.1 × 104L⊙, and the luminosity distribution is found to be well represented by the relation dNstar/dLIR ∞ L-1.65±0.14IR. We find that the ratios of the total luminosity of the sources associated with given C18O clouds to the cloud masses are significantly enhanced for those clouds associated with H II regions by an order of magnitude. This is interpreted as meaning that the formation of massive stars is enhanced due to the effects of H II regions, as is consistent with the preceding work. We have also newly found molecular outflow toward IRAS 08588–4347 as well as five possible candidates for outflows.

scholarly journals Water masers in bowshocks: Addressing the radiation pressure problem of massive star formation

2017 ◽  
Vol 13 (S336) ◽  
pp. 263-266
Author(s):  
Ross A. Burns
Keyword(s):  
Star Formation ◽  
Radiation Pressure ◽  
Massive Star ◽  
Massive Stars ◽  
Massive Star Formation ◽  
Vlbi Observations ◽  
History Of ◽  
Water Masers

AbstractEjection activities in S255IR-SMA1 and AFGL 5142 were investigated by multi-epoch VLBI observations of 22 GHz water masers, tracing bowshocks leading collimated jets. The history of ejections, revealed by the 3D maser motions and supplemented by the literature, suggests that these massive stars formed by episodic accretion, inferred via the accretion-ejection connection. This contribution centers on the role of episodic accretion in overcoming the radiation pressure problem of massive star formation - with maser VLBI and single-dish observations providing essential observational tools.

scholarly journals Discovery of Intergalactic H II Regions

2004 ◽  
Vol 217 ◽  
pp. 492-497 ◽  
Author(s):  
E. V. Ryan-Weber ◽  
M. E. Putman ◽  
K. C. Freeman ◽  
G. R. Meurer ◽  
R. L. Webster
Keyword(s):  
Star Formation ◽  
Dwarf Galaxies ◽  
Narrow Band ◽  
H Ii Regions ◽  
Metal Enrichment ◽  
Ob Stars ◽  
Neutral Gas ◽  
Starting Point ◽  
Interacting Systems

We have discovered a number of very small isolated H II regions 20-30 kpc from their nearest galaxy. The H II regions appear as tiny emission line dots (ELdots) in narrow band images obtained by the NOAO Survey for Ionization in Neutral Gas Galaxies (SINGG). We have spectroscopic confirmation of 5 isolated H II regions in 3 systems. The Hα luminosities of the H II regions are equivalent to the ionizing flux of only 1 large or a few small OB stars each. These stars appear to have formed in situ and represent atypical star formation in the low density environment of galaxy outskirts. In situ star formation in the intergalactic medium offers an alternative to galactic wind models to explain metal enrichment. In interacting systems (2 out of 3), isolated H II regions could be a starting point for tidal dwarf galaxies.

The evolution of massive bipolar jets and the birth of H II regions

1986 ◽  
Vol 64 (4) ◽  
pp. 383-386 ◽  
Author(s):  
John Ballys
Keyword(s):  
Ionizing Radiation ◽  
Ultraviolet Radiation ◽  
Stellar Evolution ◽  
Main Sequence ◽  
Massive Stars ◽  
H Ii Regions ◽  
Neutral Wind ◽  
Final Phase ◽  
Molecular Outflows ◽  
Neutral Gas

Observations suggest that outflows of neutral gas are among the first visible signs of the birth of a new star. Stars destined to be of spectral type O or B on the main sequence eventually emit large quantities of ionizing ultraviolet radiation that produce H II regions. The powerful neutral wind associated with the bipolar outflow phase of pre-main-sequence stellar evolution produces cavities in the gas surrounding a newborn star and regulates the escape of ionizing radiation from the vicinity of the star. The birth and early evolution of H II regions is the final phase in the development of bipolar, molecular outflows surrounding massive stars.

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