scholarly journals Structure and Conditions in Massive Star Forming Giant Molecular Clouds

2002 ◽  
Vol 12 ◽  
pp. 140-142
Author(s):  
Jonathan Williams
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Massive Star ◽  
Massive Stars ◽  
The Other ◽  
Giant Molecular Clouds ◽  
Star Forming ◽  
Millimeter Wavelength ◽  
Formation And Evolution ◽  
Self Similar

AbstractMassive stars form in clusters within self-gravitating molecular clouds. The size scale of these clusters is sufficiently large that non-thermal, or turbulent, motions of the gas must be taken into account when considering their formation. Millimeter wavelength radio observations of the gas and dust in these clouds reveal a complex, self-similar structure that reflects the turbulent nature of the gas. Differences are seen, however, towards dense bound cores in proto-clusters. Examination of the kinematics of gas around such cores suggests that dissipation of turbulence may be the first step in the star formation process. Newly formed stars, on the other hand, replenish turbulence through their winds and outflows. In this way, star formation may be self-regulated. Observations and simulations are beginning to demonstrate the key role that cloud turbulence plays in the formation and evolution of stellar groups.

scholarly journals Physical conditions of star forming sites in the S247/252 molecular complex

1991 ◽  
Vol 147 ◽  
pp. 443-444
Author(s):  
C. Koempe ◽  
G. Joncas ◽  
J.G.A. Wouterloot ◽  
H. Meyerdierks
Keyword(s):  
Star Formation ◽  
Molecular Complex ◽  
Molecular Clouds ◽  
Massive Stars ◽  
Giant Molecular Clouds ◽  
Star Forming ◽  
Physical Conditions ◽  
Input Parameters

By now, it is well established that massive stars form in giant molecular clouds. Numerous studies have shown that star formation, instead of being spread uniformly throughout molecular clouds, occurs in dense condensations located within these clouds. The physical conditions in these condensations are therefore critical input parameters for any theory of star formation.

scholarly journals Physical conditions of star forming sites in the S247/252 molecular complex

1991 ◽  
Vol 147 ◽  
pp. 443-444
Author(s):  
C. Koempe ◽  
G. Joncas ◽  
J.G.A. Wouterloot ◽  
H. Meyerdierks
Keyword(s):  
Star Formation ◽  
Molecular Complex ◽  
Molecular Clouds ◽  
Massive Stars ◽  
Giant Molecular Clouds ◽  
Star Forming ◽  
Physical Conditions ◽  
Input Parameters

By now, it is well established that massive stars form in giant molecular clouds. Numerous studies have shown that star formation, instead of being spread uniformly throughout molecular clouds, occurs in dense condensations located within these clouds. The physical conditions in these condensations are therefore critical input parameters for any theory of star formation.

Twinkle little stars: Massive stars are quenched in strong magnetic fields

2018 ◽  
Vol 14 (A30) ◽  
pp. 118-118
Author(s):  
Fatemeh S. Tabatabaei ◽  
M. Almudena Prieto ◽  
Juan A. Fernández-Ontiveros
Keyword(s):  
Star Formation ◽  
Magnetic Fields ◽  
Molecular Clouds ◽  
Massive Star ◽  
Massive Stars ◽  
Radio Continuum ◽  
Small Scale ◽  
Massive Star Formation ◽  
Low Mass ◽  
Formation Efficiency

AbstractThe role of the magnetic fields in the formation and quenching of stars with different mass is unknown. We studied the energy balance and the star formation efficiency in a sample of molecular clouds in the central kpc region of NGC 1097, known to be highly magnetized. Combining the full polarization VLA/radio continuum observations with the HST/Hα, Paα and the SMA/CO lines observations, we separated the thermal and non-thermal synchrotron emission and compared the magnetic, turbulent, and thermal pressures. Most of the molecular clouds are magnetically supported against gravitational collapse needed to form cores of massive stars. The massive star formation efficiency of the clouds also drops with the magnetic field strength, while it is uncorrelated with turbulence (Tabatabaei et al. 2018). The inefficiency of the massive star formation and the low-mass stellar population in the center of NGC 1097 can be explained in the following steps: I) Magnetic fields supporting the molecular clouds prevent the collapse of gas to densities needed to form massive stars. II) These clouds can then be fragmented into smaller pieces due to e.g., stellar feedback, non-linear perturbations and instabilities leading to local, small-scale diffusion of the magnetic fields. III) Self-gravity overcomes and the smaller clouds seed the cores of the low-mass stars.

scholarly journals Summary Talk: What is Happening to Massive Stars in Galaxies?

1986 ◽  
Vol 116 ◽  
pp. 523-528
Author(s):  
J. A. Graham ◽  
Taft E. Armandroff
Keyword(s):  
Star Formation ◽  
Massive Star ◽  
Massive Stars ◽  
Magellanic Clouds ◽  
Laboratory Work ◽  
Stellar Systems ◽  
Massive Star Formation ◽  
Formation And Evolution ◽  
Summary Talk

Highlights of the IAU Symposium 116 are reviewed. Some of the general themes running through the meeting are identified. These include:i) the fruitful interaction between observation, laboratory work and theory. ii) the need for understanding and, if possible, correcting for the effects of incompleteness and bias in observing lists. iii) the importance of the Magellanic Clouds, as the nearest independently evolving stellar systems, in the study of massive star formation and evolution in galaxies.

scholarly journals The elephant in the room: the importance of the details of massive star formation in molecular clouds

2019 ◽  
Vol 488 (2) ◽  
pp. 2970-2975 ◽  
Author(s):  
Michael Y Grudić ◽  
Philip F Hopkins
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Massive Star ◽  
Initial Conditions ◽  
Mass Function ◽  
Initial Mass Function ◽  
Giant Molecular Clouds ◽  
Massive Star Formation ◽  
Average Mass ◽  
Sampling Schemes

Abstract Most simulations of galaxies and massive giant molecular clouds (GMCs) cannot explicitly resolve the formation (or predict the main-sequence masses) of individual stars. So they must use some prescription for the amount of feedback from an assumed population of massive stars (e.g. sampling the initial mass function, IMF). We perform a methods study of simulations of a star-forming GMC with stellar feedback from UV radiation, varying only the prescription for determining the luminosity of each stellar mass element formed (according to different IMF sampling schemes). We show that different prescriptions can lead to widely varying (factor of ∼3) star formation efficiencies (on GMC scales) even though the average mass-to-light ratios agree. Discreteness of sources is important: radiative feedback from fewer, more-luminous sources has a greater effect for a given total luminosity. These differences can dominate over other, more widely recognized differences between similar literature GMC-scale studies (e.g. numerical methods, cloud initial conditions, presence of magnetic fields). Moreover the differences in these methods are not purely numerical: some make different implicit assumptions about the nature of massive star formation, and this remains deeply uncertain in star formation theory.

scholarly journals Properties of star forming regions in the Magellanic Clouds

2008 ◽  
Vol 4 (S256) ◽  
pp. 215-226
Author(s):  
Mónica Rubio
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Molecular Clouds ◽  
Massive Star ◽  
High Sensitivity ◽  
Magellanic Clouds ◽  
Molecular Gas ◽  
Star Forming ◽  
Star Forming Regions ◽  
Low Metallicity

AbstractUnderstanding the process of star formation in low metallicity systems is one of the key studies in the early stages of galaxy evolution. The Magellanic Clouds, being the nearest examples of low metallicity systems, allow us to study in detail their star forming regions. As a consequence of their proximity we can resolve the molecular clouds and the regions of star formation individually. Therefore we can increase our knowledge of the interaction of young luminous stars with their environment. We will present results of multiwavelenghts studies of LMC and SMC massive star forming regions, which includes properties of the cold molecular gas, the embedded young population associated with molecular clouds, and the interaction of newly born stars with the surrounding interstellar medium, based on ASTE and APEX submillimeter observations complemented high sensitivity NIR groud based observations and Spitzer results.

scholarly journals Dense molecular clouds and associated star formation in the Magellanic Clouds

2006 ◽  
Vol 2 (S237) ◽  
pp. 40-46
Author(s):  
Mónica Rubio
Keyword(s):  
Star Formation ◽  
Uv Radiation ◽  
Molecular Clouds ◽  
Massive Star ◽  
Dust Emission ◽  
Young Stellar Objects ◽  
Continuum Emission ◽  
Giant Molecular Clouds ◽  
Stellar Objects ◽  
Ir Sources

AbstractMultiwavelengths studies of massive star formation regions in the LMC and SMC reveal that a second generation of stars is being formed in dense molecular clouds located in the surroundings of the massive clusters. These dense molecular clouds have survived the action of massive star UV radiation fields and winds and they appear as compact dense H2 knots in regions of weak CO emission. Alternatively, we have found that large molecular clouds, probably remnants of the parental giant molecular clouds where the first generation of stars were formed, are suffering the interaction of the winds and UV radiation field in their surfaces in the direction of the central massive cluster or massive stars. These molecular regions show 1.2 mm continuum emission form cold dust and they show embedded IR sources as determined from deep ground base JHKs imaging. The distribution of young IR sources as determined from their Mid IR colors obtained by SPITZER concentrate in the maxima of CO and dust emission. IR spectroscopy of the embedded sources with high IR excess confirm their nature as massive young stellar objects (MYSO's). Our results are suggestive of contagious star formation where triggering and induced star formation could be taking place.

scholarly journals The VLT-FLAMES Tarantula Survey

2018 ◽  
Vol 618 ◽  
pp. A73 ◽  
Author(s):  
F. R. N. Schneider ◽  
O. H. Ramírez-Agudelo ◽  
F. Tramper ◽  
J. M. Bestenlehner ◽  
N. Castro ◽  
...  
Keyword(s):  
Star Formation ◽  
Massive Star ◽  
Massive Stars ◽  
High Redshift ◽  
Large Magellanic Cloud ◽  
Giant Molecular Clouds ◽  
Stellar Content ◽  
Massive Star Formation ◽  
Hii Region ◽  
Mass Distributions

The 30 Doradus (30 Dor) nebula in the Large Magellanic Cloud (LMC) is the brightest HII region in the Local Group and a prototype starburst similar to those found in high redshift galaxies. It is thus a stepping stone to understand the complex formation processes of stars in starburst regions across the Universe. Here, we have studied the formation history of massive stars in 30 Dor using masses and ages derived for 452 mainly OB stars from the spectroscopic VLT-FLAMES Tarantula Survey (VFTS). We find that stars of all ages and masses are scattered throughout 30 Dor. This is remarkable because it implies that massive stars either moved large distances or formed independently over the whole field of view in relative isolation. We find that both channels contribute to the 30 Dor massive star population. Massive star formation rapidly accelerated about 8 Myr ago, first forming stars in the field before giving birth to the stellar populations in NGC 2060 and NGC 2070. The R136 star cluster in NGC 2070 formed last and, since then, about 1 Myr ago, star formation seems to be diminished with some continuing in the surroundings of R136. Massive stars within a projected distance of 8 pc of R136 are not coeval but show an age range of up to 6 Myr. Our mass distributions are well populated up to 200 M⊙. The inferred IMF is shallower than a Salpeter-like IMF and appears to be the same across 30 Dor. By comparing our sample of stars to stellar models in the Hertzsprung–Russell diagram, we find evidence for missing physics in the models above log L/L⊙ = 6 that is likely connected to enhanced wind mass loss for stars approaching the Eddington limit. Our work highlights the key information about the formation, evolution and final fates of massive stars encapsulated in the stellar content of 30 Dor, and sets a new benchmark for theories of massive star formation in giant molecular clouds.

scholarly journals Molecular Clouds: Internal Properties, Turbulence, Star Formation and Feedback

2012 ◽  
Vol 8 (S292) ◽  
pp. 19-28 ◽  
Author(s):  
Jonathan C. Tan ◽  
Suzanne N. Shaske ◽  
Sven Van Loo
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Cluster Formation ◽  
Dynamical Evolution ◽  
Theoretical Models ◽  
Giant Molecular Clouds ◽  
Star Forming ◽  
Cloud Dynamics ◽  
Star Formation Activity ◽  
Internal Properties

AbstractAll stars are born in molecular clouds, and most in giant molecular clouds (GMCs), which thus set the star formation activity of galaxies. We first review their observed properties, including measures of mass surface density, Σ, and thus mass,M. We discuss cloud dynamics, concluding most GMCs are gravitationally bound. Star formation is highly clustered within GMCs, but overall is very inefficient. We compare properties of star-forming clumps with those of young stellar clusters (YSCs). The high central densities of YSCs may result via dynamical evolution of already-formed stars during and after star cluster formation. We discuss theoretical models of GMC evolution, especially addressing how turbulence is maintained, and emphasizing the importance of GMC collisions. We describe how feedback limits total star formation efficiency, ε, in clumps. A turbulent and clumpy medium allows higher ε, permitting formation of bound clusters even when escape speeds are less than the ionized gas sound speed.

scholarly journals Fast cloud–cloud collisions in a strongly barred galaxy: suppression of massive star formation

2020 ◽  
Vol 494 (2) ◽  
pp. 2131-2146 ◽  
Author(s):  
Yusuke Fujimoto ◽  
Fumiya Maeda ◽  
Asao Habe ◽  
Kouji Ohta
Keyword(s):  
Star Formation ◽  
Massive Star ◽  
Massive Stars ◽  
Extreme Environment ◽  
Bound State ◽  
Observational Evidence ◽  
Giant Molecular Clouds ◽  
Massive Star Formation ◽  
Barred Galaxies ◽  
Cloud Properties

ABSTRACT Recent galaxy observations show that star formation activity changes depending on galactic environments. In order to understand the diversity of galactic-scale star formation, it is crucial to understand the formation and evolution of giant molecular clouds in an extreme environment. We focus on observational evidence that bars in strongly barred galaxies lack massive stars even though quantities of molecular gas are sufficient to form stars. In this paper, we present a hydrodynamical simulation of a strongly barred galaxy, using a stellar potential which is taken from observational results of NGC 1300, and we compare cloud properties between different galactic environments: bar, bar-end, and spiral arms. We find that the mean of cloud’s virial parameter is αvir ∼ 1 and that there is no environmental dependence, indicating that the gravitationally bound state of a cloud is not behind the observational evidence of the lack of massive stars in strong bars. Instead, we focus on cloud–cloud collisions, which have been proposed as a triggering mechanism for massive star formation. We find that the collision speed in the bar is faster than those in the other regions. We examine the collision frequency using clouds’ kinematics and conclude that the fast collisions in the bar could originate from random-like motion of clouds due to elliptical gas orbits shifted by the bar potential. These results suggest that the observed regions of lack of active star formation in the strong bar originate from the fast cloud–cloud collisions, which are inefficient in forming massive stars, due to the galactic-scale violent gas motion.

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