scholarly journals TRAO Survey of the Nearby Filamentary Molecular Clouds, the Universal Nursery of Stars (TRAO FUNS). II. Filaments and Dense Cores in IC 5146

2021 ◽  
Vol 919 (1) ◽  
pp. 3
Author(s):  
Eun Jung Chung ◽  
Chang Won Lee ◽  
Shinyoung Kim ◽  
Maheswar Gopinathan ◽  
Mario Tafalla ◽  
...  
Keyword(s):  
Molecular Clouds ◽  
Dense Cores

scholarly journals The global star formation law: from dense cores to extreme starbursts

2006 ◽  
Vol 2 (S237) ◽  
pp. 331-335
Author(s):  
Yu Gao
Keyword(s):  
Star Formation ◽  
Linear Correlation ◽  
Molecular Clouds ◽  
High Redshift ◽  
Gas Content ◽  
Molecular Gas ◽  
Giant Molecular Clouds ◽  
Active Star ◽  
Dense Cores ◽  
The Galaxy

AbstractActive star formation (SF) is tightly related to the dense molecular gas in the giant molecular clouds' dense cores. Our HCN (measure of the dense molecular gas) survey in 65 galaxies (including 10 ultraluminous galaxies) reveals a tight linear correlation between HCN and IR (SF rate) luminosities, whereas the correlation between IR and CO (measure of the total molecular gas) luminosities is nonlinear. This suggests that the global SF rate depends more intimately upon the amount of dense molecular gas than the total molecular gas content. This linear relationship extends to both the dense cores in the Galaxy and the hyperluminous extreme starbursts at high-redshift. Therefore, the global SF law in dense gas appears to be linear all the way from dense cores to extreme starbursts, spanning over nine orders of magnitude in IR luminosity.

scholarly journals Head-on collisions: how to bring large quantities of gas out of inner disks

2004 ◽  
Vol 217 ◽  
pp. 420-421
Author(s):  
Jonathan Braine ◽  
U. Lisenfeld ◽  
P.-A. Duc
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Intergalactic Medium ◽  
Spiral Galaxies ◽  
Molecular Gas ◽  
Hii Region ◽  
Neutral Gas ◽  
Dense Cores ◽  
Clear Cases ◽  
Formation Efficiency

Head-on collisions of spiral galaxies can bring large quantities of gas out of spiral disks and into the intergalactic medium. Only two clear cases (UGC 12914/5 and UGC 813/6) of such collisions are known (Condon et al. 1993, 2002) and in both cases several 109 M⊙ of neutral gas is found in the bridge between the two galaxies which are now separating. About half of the gas is molecular. The gas, atomic or molecular, is brought out by collisions between clouds, which then acquire an intermediate velocity and end up between the galaxies. The bridges contain no old stars and in each case only one HII region despite the large masses of molecular gas, such that the star formation efficiency is very low in the bridges. The collisions occurred 20 – 50 million years ago, much greater than the collapse time for dense cores. We (Braine et al. 2003, 2004) show that collisions between molecular clouds, and not only between atomic gas clouds, bring gas into the bridges. It is not currently known whether the galaxies and bridges are bound or whether they will continue to separate, releasing several 109 M⊙ of neutral gas into the intergalactic medium.

A physically motivated core definition applied to dust emission observations of the Pipe nebula

2018 ◽  
Vol 14 (S345) ◽  
pp. 259-260
Author(s):  
Birgit Hasenberger ◽  
João Alves
Keyword(s):  
Star Formation ◽  
Formation Process ◽  
Molecular Clouds ◽  
Dust Emission ◽  
Core Sample ◽  
Critical Stage ◽  
The Core ◽  
Dense Cores ◽  
A New Technique ◽  
Cloud Medium

AbstractDense cores represent a critical stage in the star-formation process, but are not physically well-defined entities. We present a new technique to define core boundaries in observations of molecular clouds based on the physical properties of the cloud medium. Applying this technique to regions in the Pipe nebula, we find that our core boundaries differ from previous analyses, with potentially crucial implications for the statistical properties of the core sample.

scholarly journals Magnetic Fields in Molecular Clouds

2004 ◽  
Vol 221 ◽  
pp. 83-96
Author(s):  
Tyler L. Bourke ◽  
Alyssa A. Goodman
Keyword(s):  
Star Formation ◽  
Magnetic Fields ◽  
Observational Data ◽  
Observational Studies ◽  
Molecular Clouds ◽  
Large Scale ◽  
Angular Resolution ◽  
Protoplanetary Disks ◽  
High Angular Resolution ◽  
Dense Cores

Magnetic fields are believed to play an important role in the evolution of molecular clouds, from their large scale structure to dense cores, protostellar envelopes, and protoplanetary disks. How important is unclear, and whether magnetic fields are the dominant force driving star formation at any scale is also unclear. In this review we examine the observational data which address these questions, with particular emphasis on high angular resolution observations. Unfortunately the data do not clarify the situation. It is clear that the fields are important, but to what degree we don't yet know. Observations to date have been limited by the sensitivity of available telescopes and instrumentation. In the future ALMA and the SKA in particular should provide great advances in observational studies of magnetic fields, and we discuss which observations are most desirable when they become available.

scholarly journals A search for small-scale clumpiness in dense cores of molecular clouds

2008 ◽  
Vol 52 (12) ◽  
pp. 963-975 ◽  
Author(s):  
L. E. Pirogov ◽  
I. I. Zinchenko
Keyword(s):  
Molecular Clouds ◽  
Small Scale ◽  
Dense Cores

scholarly journals Characteristics of H2CO Towards Star-Forming Regions

1987 ◽  
Vol 115 ◽  
pp. 171-171
Author(s):  
H. R. Dickel ◽  
W. M. Goss ◽  
A. H. Rots
Keyword(s):  
Molecular Clouds ◽  
H Ii Regions ◽  
Star Forming ◽  
Star Forming Regions ◽  
Compact Region ◽  
Dense Cores ◽  
H Ii Region ◽  
Narrow Width ◽  
Water Masers ◽  
Small Clusters

Small clusters of recently-formed massive stars with their associated compact H II regions are often found embedded in the dense cores of molecular clouds. The H2CO opacity is correlated with the compactness of the H II region and is especially high for those with associated maser activity although additional factors are involved for the ultra-compact H II regions (UCH II). VLA observations of H2CO at 2 cm have been made towards the UCH II regions of W49-north. The highest H2CO opacity of 1.0 is found towards region A which does not have maser activity; yet one of the most compact region C, has an H2CO opacity of only 0.3, For these sources the integrated H2CO opacity (over the entire profile) may be more indicative of compactness. This may be due to the broader H2CO lines which can occur towards the maser regions. For example, large line widths of 10 to 12 km s−1 ate found towards W49-north G where the most intense water masers are located and towards W49-north B which has OH masers. The H2CO line with the highest 2 cm opacity of 2.5 and a narrow width of 2 km s−1 is found towards the UCH II region ON 3 which has only weak H2O maser emission.

scholarly journals Filament Fragmentation

2001 ◽  
Vol 200 ◽  
pp. 391-400 ◽  
Author(s):  
Shu-ichiro Inutsuka ◽  
Toru Tsuribe
Keyword(s):  
Molecular Clouds ◽  
Mass Function ◽  
Mass Scale ◽  
Thermal Processes ◽  
Dense Cores ◽  
Dense Molecular Cloud ◽  
Basic Physics ◽  
Formation And Evolution ◽  
Field Lines ◽  
Cloud Cores

The formation and evolution processes of magnetized filamentary molecular clouds are investigated in detail by linear stability analyses and non-linear numerical calculations. A one-dimensionally compressed self-gravitating sheet-like cloud breaks up into filamentary clouds. The directions of the longitudinal axes of the resulting filaments are perpendicular to the directions of magnetic field lines unless the column density of the sheet is very small. These magnetized filaments tend to collapse radially without characteristic density, length, and mass scale for the further fragmentation during the isothermal phase. The characteristic minimum mass for the final fragmentation is obtained by the investigation of thermal processes. The essential points of the above processes are analytically explained in terms of the basic physics. A theory for the expected mass function of dense molecular cloud cores is obtained. The expected mean surface density of companions of dense cores is also discussed.

scholarly journals Massive core/star formation triggered by cloud–cloud collision: Effect of magnetic field

2020 ◽  
Author(s):  
Nirmit Sakre ◽  
Asao Habe ◽  
Alex R Pettitt ◽  
Takashi Okamoto
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Magnetic Fields ◽  
Strong Magnetic Field ◽  
Molecular Clouds ◽  
Weak Magnetic Field ◽  
Dense Cores ◽  
Cloud Models ◽  
Low Mass ◽  
Magnetohydrodynamic Simulations

Abstract We study the effect of magnetic field on massive dense core formation in colliding unequal molecular clouds by performing magnetohydrodynamic simulations with sub-parsec resolution (0.015 pc) that can resolve the molecular cores. Initial clouds with the typical gas density of the molecular clouds are immersed in various uniform magnetic fields. The turbulent magnetic fields in the clouds consistent with the observation by Crutcher et al. (2010, ApJ, 725, 466) are generated by the internal turbulent gas motion before the collision, if the uniform magnetic field strength is 4.0 μG. The collision speed of 10 km s−1 is adopted, which is much larger than the sound speeds and the Alfvén speeds of the clouds. We identify gas clumps with gas densities greater than 5 × 10−20 g cm−3 as the dense cores and trace them throughout the simulations to investigate their mass evolution and gravitational boundness. We show that a greater number of massive, gravitationally bound cores are formed in the strong magnetic field (4.0 μG) models than the weak magnetic field (0.1 μG) models. This is partly because the strong magnetic field suppresses the spatial shifts of the shocked layer that should be caused by the nonlinear thin shell instability. The spatial shifts promote the formation of low-mass dense cores in the weak magnetic field models. The strong magnetic fields also support low-mass dense cores against gravitational collapse. We show that the numbers of massive, gravitationally bound cores formed in the strong magnetic field models are much larger than in the isolated, non-colliding cloud models, which are simulated for comparison. We discuss the implications of our numerical results on massive star formation.

scholarly journals Constraining How Star Formation Proceeds: Surveys in the Sub-mm and FIR

2009 ◽  
Vol 5 (H15) ◽  
pp. 406-407
Author(s):  
Doug Johnstone
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Mass Star ◽  
Star Forming ◽  
Physical Conditions ◽  
Star Forming Regions ◽  
Dense Cores ◽  
Multi Wavelength ◽  
Low Mass ◽  
High Column

AbstractCoordinated multi-wavelength surveys of molecular clouds are providing strong constraints on the physical conditions within low-mass star-forming regions. In this manner, Perseus and Ophiuchus have been exceptional laboratories for testing the earliest phases of star formation. Highlights of these results are: (1) dense cores form only in high column density regions, (2) dense cores contain only a few percent of the cloud mass, (3) the mass distribution of the dense cores is similar to the IMF, (4) the more massive cores are most likely to contain embedded protostars, and (5) the kinematics of the dense cores and the bulk gas show significant coupling.

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