scholarly journals Molecular Clouds in the LMC Observed with NANTEN: III. Comparison with HII Regions

1999 ◽  
Vol 190 ◽  
pp. 130-131
Author(s):  
R. Abe ◽  
A. Hara ◽  
T. Hayakawa ◽  
S. Kato ◽  
A. Kawamura ◽  
...  
Keyword(s):  
Molecular Clouds ◽  
Hii Regions ◽  
Stellar Clusters ◽  
Giant Molecular Clouds

We have made 12CO(J=1-0) observations in the LMC with NANTEN, and compared the detected giant molecular clouds (GMCs) with HII regions and stellar clusters. It is found that ~ 80% of the GMCs are associated with HII regions. The results of comparisons of the GMCs with the HII regions and the stellar clusters are presented.

scholarly journals A 12CO Survey of the LMC with NANTEN

1999 ◽  
Vol 190 ◽  
pp. 61-66
Author(s):  
Y. Fukui ◽  
R. Abe ◽  
A. Hara ◽  
T. Hayakawa ◽  
S. Kato ◽  
...  
Keyword(s):  
Molecular Clouds ◽  
Cluster Formation ◽  
Hii Regions ◽  
Stellar Clusters ◽  
Giant Molecular Clouds

We have made a 12CO(J = 1−0) survey of the LMC with NANTEN. A sample of 55 giant molecular clouds has been identified and comparisons with stellar clusters, HII regions and SNRs are presented. The connection between the clouds and cluster formation is discussed.

scholarly journals The Disruption of the Molecular Cloud Associated with the North America and Pelican Nebulae

1980 ◽  
Vol 87 ◽  
pp. 151-156
Author(s):  
John Bally
Keyword(s):  
North America ◽  
Radio Astronomy ◽  
Molecular Clouds ◽  
Hii Regions ◽  
Relative Importance ◽  
Giant Molecular Clouds ◽  
Extensive Investigation ◽  
Astronomy Observatory ◽  
The North ◽  
College Radio

Giant molecular clouds can be destroyed in several ways: by conversion of gas into stars; by dissociation of H2 into HI; by ionization and formation of HII regions; and by dispersal of the cloud into cloudets. The relative importance of these processes can be assessed by observations of evolved HII regions and associated molecular clouds. A number of such complexes have been studied in 12CO at the Five College Radio Astronomy Observatory (FCRAO) as part of an extensive investigation of clouds associated with about 60 Sharpless HII regions. A particularly clear example of cloud disruption is found in the case of W80, the North America and Pelican Nebulae in Cygnus (Bally and Scoville 1980).

scholarly journals Molecular Clouds in the LMC Observed with NANTEN: II. Comparison with Stellar Clusters

1999 ◽  
Vol 190 ◽  
pp. 150-151
Author(s):  
R. Yamaguchi ◽  
R. Abe ◽  
A. Hara ◽  
T. Hayakawa ◽  
S. Kato ◽  
...  
Keyword(s):  
Millimeter Wave ◽  
Molecular Clouds ◽  
Detailed Comparison ◽  
Stellar Clusters ◽  
Giant Molecular Clouds

We have made 12CO(J=1−0) observations of the LMC with the NANTEN millimeter-wave telescope and identified about 100 distinct giant molecular clouds (GMCs). A detailed comparison of the GMCs with stellar clusters and a UV image is discussed.

scholarly journals Rise and fall of molecular clouds across the M 33 disk

2019 ◽  
Vol 622 ◽  
pp. A171 ◽  
Author(s):  
Edvige Corbelli ◽  
Jonathan Braine ◽  
Carlo Giovanardi
Keyword(s):  
Molecular Clouds ◽  
Line Emission ◽  
Molecular Gas ◽  
Stellar Clusters ◽  
Giant Molecular Clouds ◽  
Hii Region ◽  
Star Forming ◽  
Outer Disk ◽  
Low Mass ◽  
The Mean

We carried out deep searches for CO line emission in the outer disk of M 33, at R >  7 kpc, and examined the dynamical conditions that can explain variations in the mass distribution of the molecular cloud throughout the disk of M 33. We used the IRAM-30 m telescope to search for CO lines in the outer disk toward 12 faint mid-infrared (MIR) selected sources and in an area of the southern outer disk hosting MA1, a bright HII region. We detect narrow CO lines at the location of two MIR sources at galactocentric distances of about 8 kpc that are associated with low-mass young stellar clusters, and at four locations in the proximity of MA1. The paucity of CO lines at the location of weak MIR-selected sources probably arises because most of them are not star-forming sites in M 33, but background sources. Although very uncertain, the total molecular mass of the detected clouds around MA1 is lower than expected given the stellar mass of the cluster, because dispersal of the molecular gas is taking place as the HII region expands. The mean mass of the giant molecular clouds (GMCs) in M 33 decreases radially by a factor 2 from the center out to 4 kpc, then it stays constant until it drops at R >  7 kpc. We suggest that GMCs become more massive toward the center because of the fast rotation of the disk, which drives mass growth by coalescence of smaller condensations as they cross the arms. The analysis of both HI and CO spectral data gives the consistent result that corotation of the two main arms in this galaxy is at a radius of 4.7 ± 0.3 kpc, and spiral shock waves become subsonic beyond 3.9 kpc. Perturbations are quenched beyond 6.5 kpc, where CO lines have been detected only around sporadic condensations associated with UV and MIR emission.

scholarly journals Physical Processes in Massive Star Formation

1986 ◽  
Vol 116 ◽  
pp. 301-315
Author(s):  
Joseph Silk
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Massive Star ◽  
Hii Regions ◽  
Stellar Mass ◽  
Giant Molecular Clouds ◽  
Physical Processes ◽  
Massive Star Formation ◽  
The Imf

The gravitational fragmentation theory of star formation is reviewed. Theoretical arguments are presented which suggest that the lower stellar mass cut-off to the IMF in giant HII regions may be as high as 10 M⊙. Mechanisms for bimodal star formation are described in the context of a coagulation model for formation of the giant molecular clouds, and application is made to starbursting galaxies.

scholarly journals Giant molecular clouds and star formation in the Large Magellanic Cloud

2006 ◽  
Vol 2 (S237) ◽  
pp. 101-105
Author(s):  
A. Kawamura ◽  
T. Minamidani ◽  
Y. Mizuno ◽  
T. Onishi ◽  
N. Mizuno ◽  
...  
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Cluster Formation ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Stellar Clusters ◽  
Giant Molecular Clouds ◽  
Surface Mass ◽  
Complete Survey ◽  
Physical Quantities

AbstractIn order to elucidate star formation in the Large Magellanic Cloud, a complete survey of the molecular clouds was carried out by NANTEN. In this work, we compare 230 giant molecular clouds (GMCs), whose physical quantities are well determined, with young clusters and Hii regions. We find that about 76% of the GMCs are actively forming stars or clusters, while 24% show no signs of massive star or cluster formation. Effects of supergiant shells (SGSs) on the formation of GMCs and stars are also studied. The number and surface mass densities of the GMCs are higher by a factor of 1.5–2 at the edge of the SGSs than elsewhere. It is also found that young stellar clusters are more actively formed in the GMCs facing to the center of the SGSs. These results are consistent with the previous studies by Yamaguchi et al. and suggest the formation of GMCs and the cluster is triggered by dynamical effects of the SGSs.

scholarly journals NANTEN Observations of the LMC: Giant Molecular Clouds as Formation Sites of Stellar Clusters

2002 ◽  
Vol 207 ◽  
pp. 684-686
Author(s):  
Norikazu Mizuno ◽  
Reiko Yamaguchi ◽  
Toshikazu Onishi ◽  
Akira Mizuno ◽  
Yasuo Fukui
Keyword(s):  
Molecular Clouds ◽  
Cluster Formation ◽  
Peak Position ◽  
Compact Groups ◽  
H Ii Regions ◽  
Stellar Clusters ◽  
Giant Molecular Clouds ◽  
Complete Sample ◽  
Linear Resolution ◽  
Carbon Monoxide Emission

A CO survey of the LMC has been completed in the J = 1−0 carbon monoxide emission at 2.6 mm wavelength with NANTEN. This survey has revealed the first complete sample of giant molecular clouds (GMCs) in the LMC at a linear resolution of ∼ 40 pc. The GMCs exhibit a good spatial correlation with youngest stellar clusters often associated with the giant H II regions. The ages of clusters associated with GMCs are fairly young, ≲ 10 Myr, demonstrating that cluster formation is ongoing in these GMCs. In addition, compact groups of the young clusters are often found at the peak position of the GMCs, e.g., N159 and N44, while much looser groups are away from the GMCs. This suggests that the clusters are formed in groups and are dispersed as they become old.

scholarly journals Molecules in the Magellanic Clouds

1991 ◽  
Vol 148 ◽  
pp. 415-420 ◽  
Author(s):  
R. S. Booth ◽  
Th. De Graauw
Keyword(s):  
High Resolution ◽  
Molecular Clouds ◽  
Short Review ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Magellanic Clouds ◽  
Giant Molecular Clouds ◽  
Interstellar Molecules ◽  
First Time ◽  
Excitation Conditions

In this short review we describe recent new observations of millimetre transitions of molecules in selected regions of the Magellanic Clouds. The observations were made using the Swedish-ESO Submillimetre Telescope, SEST, (Booth et al. 1989), the relatively high resolution of which facilitates, for the first time, observations of individual giant molecular clouds in the Magellanic Clouds. We have mapped the distribution of the emission from the two lowest rotational transitions of 12CO and 13CO and hence have derived excitation conditions for the molecule. In addition, we have observed several well-known interstellar molecules in the same regions, thus doubling the number of known molecules in the Large Magellanic Cloud (LMC). The fact that all the observations have been made under controlled conditions with the same telescope enables a reasonable intercomparison of the molecular column densities. In particular, we are able to observe the relative abundances among the different isotopically substituted species of CO.

scholarly journals Effects of initial density profiles on massive star cluster formation in giant molecular clouds

2021 ◽  
Author(s):  
Yingtian Chen ◽  
Hui Li ◽  
Mark Vogelsberger
Keyword(s):  
Angular Momentum ◽  
Star Formation ◽  
Molecular Clouds ◽  
Globular Clusters ◽  
Cluster Formation ◽  
Initial Density ◽  
Giant Molecular Clouds ◽  
Density Profiles ◽  
Stellar Feedback ◽  
Gas Accretion

Abstract We perform a suite of hydrodynamic simulations to investigate how initial density profiles of giant molecular clouds (GMCs) affect their subsequent evolution. We find that the star formation duration and integrated star formation efficiency of the whole clouds are not sensitive to the choice of different profiles but are mainly controlled by the interplay between gravitational collapse and stellar feedback. Despite this similarity, GMCs with different profiles show dramatically different modes of star formation. For shallower profiles, GMCs first fragment into many self-gravitation cores and form sub-clusters that distributed throughout the entire clouds. These sub-clusters are later assembled ‘hierarchically’ to central clusters. In contrast, for steeper profiles, a massive cluster is quickly formed at the center of the cloud and then gradually grows its mass via gas accretion. Consequently, central clusters that emerged from clouds with shallower profiles are less massive and show less rotation than those with the steeper profiles. This is because 1) a significant fraction of mass and angular momentum in shallower profiles is stored in the orbital motion of the sub-clusters that are not able to merge into the central clusters 2) frequent hierarchical mergers in the shallower profiles lead to further losses of mass and angular momentum via violent relaxation and tidal disruption. Encouragingly, the degree of cluster rotations in steeper profiles is consistent with recent observations of young and intermediate-age clusters. We speculate that rotating globular clusters are likely formed via an ‘accretion’ mode from centrally-concentrated clouds in the early Universe.

scholarly journals The Ballistic Particle Model

1983 ◽  
Vol 100 ◽  
pp. 133-134
Author(s):  
Frank N. Bash
Keyword(s):  
Radial Velocity ◽  
Gravitational Potential ◽  
Molecular Clouds ◽  
Milky Way ◽  
Terminal Velocity ◽  
Particle Model ◽  
The Sun ◽  
Giant Molecular Clouds ◽  
Spiral Pattern ◽  
Armed Spiral

Bash and Peters (1976) suggested that giant molecular clouds (GMC's) can be viewed as ballistic particles launched from the two-armed spiral-shock (TASS) wave with orbits influenced only by the overall galactic gravitational potential perturbed by the spiral gravitational potential in the arms. For GMC's in the Milky Way, the model predicts that the radial velocity observed from the Sun increases with age (time since launch). We showed that the terminal velocity of CO observed from l ≃ 30° to l ≃ 60° can be understood if all GMC's are born in the spiral pattern given by Yuan (1969) and live 30 × 106 yrs. Older GMC's were predicted to have radial velocities which exceed observed terminal velocities.

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