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 On the compressive nature of turbulence driven by ionizing feedback in the pillars of the Carina Nebula

2020 ◽  
Vol 500 (2) ◽  
pp. 1721-1740
Author(s):  
Shyam H Menon ◽  
Christoph Federrath ◽  
Pamela Klaassen ◽  
Rolf Kuiper ◽  
Megan Reiter
Keyword(s):  
Star Formation ◽  
Ionizing Radiation ◽  
Molecular Clouds ◽  
Large Scale ◽  
Massive Stars ◽  
Driving Mode ◽  
Average Value ◽  
Neutral Gas ◽  
Carina Nebula ◽  
Spiral Arm

ABSTRACT The ionizing radiation of massive stars sculpts the surrounding neutral gas into pillar-like structures. Direct signatures of star formation through outflows and jets are observed in these structures, typically at their tips. Recent numerical simulations have suggested that this star formation could potentially be triggered by photoionizing radiation, driving compressive modes of turbulence in the pillars. In this study, we use recent high-resolution ALMA observations of 12CO, 13CO, and C18O, J = 2 − 1 emission to test this hypothesis for pillars in the Carina Nebula. We analyse column density and intensity-weighted velocity maps, and subtract any large-scale bulk motions in the plane of the sky to isolate the turbulent motions. We then reconstruct the dominant turbulence driving mode in the pillars, by computing the turbulence driving parameter b, characterized by the relation $\sigma _{\rho /\rho _0} = b \mathcal {M}$ between the standard deviation of the density contrast $\sigma _{\rho /\rho _0}$ (with gas density ρ and its average ρ0) and the turbulent Mach number $\mathcal {M}$. We find values of b ∼ 0.7–1.0 for most of the pillars, suggesting that predominantly compressive modes of turbulence are driven in the pillars by the ionizing radiation from nearby massive stars. We find that this range of b values can produce star formation rates in the pillars that are a factor ∼3 greater than with b ∼ 0.5, a typical average value of b for spiral-arm molecular clouds. Our results provide further evidence for the potential triggering of star formation in pillars through compressive turbulent motions.

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.

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.

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 Evolved massive stars in W33 and in GMC G23.3 − 0.3

2015 ◽  
Vol 12 (S316) ◽  
pp. 167-168
Author(s):  
M. Messineo ◽  
J. S. Clark ◽  
D. F. Figer ◽  
K. M. Menten ◽  
R.-P. Kudritzki ◽  
...  
Keyword(s):  
Star Formation ◽  
Ionizing Radiation ◽  
Molecular Clouds ◽  
Massive Stars ◽  
Molecular Complexes ◽  
Star Formation History ◽  
Precise Information ◽  
Spatial And Temporal Distributions ◽  
Formation History ◽  
History Of

AbstractWe conducted infrared spectroscopic observations of bright stars in the direction of the molecular clouds W33 and GMC G23.3 − 0.3. We compared stellar spectro-photometric distances with parallactic distances to these regions, and we were able to assess the association of the detected massive stars with these molecular complexes. The spatial and temporal distributions of the detected stars enabled us to locate sources of ionizing radiation and to gather precise information on the star formation history of these clouds. The studied clouds present different distributions of massive stars.

scholarly journals Surround and Squash: the impact of superbubbles on the interstellar medium in Scorpius–Centaurus OB2

2018 ◽  
Vol 619 ◽  
pp. A120 ◽  
Author(s):  
Martin G. H. Krause ◽  
Andreas Burkert ◽  
Roland Diehl ◽  
Katharina Fierlinger ◽  
Benjamin Gaczkowski ◽  
...  
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Massive Star ◽  
Massive Stars ◽  
Three Dimensional ◽  
X Rays ◽  
Hot Gas ◽  
Sky Survey ◽  
Hydrodynamical Simulations ◽  
The Impact

Context. Feedback by massive stars shapes the interstellar medium and is thought to influence subsequent star formation. The details of this process are under debate. Aims. We exploited observational constraints on stars, gas, and nucleosynthesis ashes for the closest region with recent massive-star formation, Scorpius–Centaurus OB2, and combined them with three-dimensional (3D) hydrodynamical simulations in order to address the physics and history of the Scorpius–Centaurus superbubble. Methods. We used published cold gas observations of continuum and molecular lines from Planck, Herschel, and APEX. We analysed the Galactic All Sky Survey (GASS) to investigate shell structures in atomic hydrogen, and used Hipparcos and Gaia data in combination with interstellar absorption against stars to obtain new constraints for the distance to the Hi features. Hot gas is traced in soft X-rays via the ROSAT all sky survey. Nucleosynthesis ejecta from massive stars were traced with new INTEGRAL spectrometer observations via 26Al radioactivity. We also performed 3D hydrodynamical simulations for the Sco–Cen superbubble. Results. Soft X-rays and a now more significant detection of 26Al confirm recent (≈1 Myr ago) input of mass, energy, and nucleosynthesis ejecta, likely from a supernova in the Upper Scorpius (USco) subgroup. We confirm a large supershell around the entire OB association and perform a 3D hydrodynamics simulation with a conservative massive star population that reproduces the morphology of the superbubble. High-resolution GASS observations reveal a nested, filamentary supershell. The filaments are possibly related to the Vishniac clumping instability, but molecular gas (Lupus I) is only present where the shell coincides with the connecting line between the subgroups of the OB association, suggesting a connection to the cloud, probably an elongated sheet, out of which the OB association formed. Stars have formed sequentially in the subgroups of the OB association and currently form in Lupus I. To investigate the impact of massive star feedback on extended clouds, we simulate the interaction of a turbulent cloud with the hot, pressurised gas in a superbubble. The hot gas fills the tenuous regions of the cloud and compresses the denser parts. Stars formed in these dense clumps would have distinct spatial and kinematic distributions. Conclusions. The combined results from observations and simulations are consistent with a scenario where dense gas was initially distributed in a band elongated in the direction now occupied by the OB association. Superbubbles powered by massive stars would then repeatedly break out of the elongated parent cloud, and surround and squash the denser parts of the gas sheet and thus induce more star formation. The expected spatial and kinematic distribution of stars is consistent with observations of Sco–Cen. The scenario might apply to many similar regions in the Galaxy and also to active galactic nucleus (AGN)-related superbubbles.

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 On the Propagation and Structure of Ionization Fronts

1958 ◽  
Vol 8 ◽  
pp. 1062-1068
Author(s):  
F. A. Goldsworthy
Keyword(s):  
Shock Wave ◽  
Ionizing Radiation ◽  
Atomic Hydrogen ◽  
Hydrogen Gas ◽  
Ionization Front ◽  
Ionized Gas ◽  
Hii Region ◽  
Ionization Fronts ◽  
Neutral Gas ◽  
Gravitational Equilibrium

The problem discussed here is that of determining the motion of a cloud of neutral atomic hydrogen gas, when it is subjected to ionizing radiation from a star embedded in it. Initially the gas is in gravitational equilibrium at a constant temperature of about 100°K. It is supposed that at time t=0 the star suddenly begins to radiate with a certain intensity, which remains constant thereafter. Part of the surrounding gas will be ionized and an ionization front (separating the ionized gas from the neutral gas) will move outwards into the neutral gas. A shock wave may also propagate ahead of the ionization front into the neutral gas. There will therefore be two regions to consider—a region of ionized gas (HII region) and a region of neutral gas (HI region) in which there may be a shock.

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.

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