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 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 Relations Between Star Formation and the Interstellar Medium

1998 ◽  
Vol 179 ◽  
pp. 165-171 ◽  
Author(s):  
Y. Fukui ◽  
Y. Yonekura
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Formation Process ◽  
Molecular Clouds ◽  
Future Prospects

We review observational results concerning star formation and dense molecular clouds, the interstellar medium most relevant to star-formation process, as well as future prospects.

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.

scholarly journals The connection between prestellar cores and filaments in the Aquila molecular cloud complex

2015 ◽  
Vol 11 (S315) ◽  
Author(s):  
Vera Könyves ◽  
Philippe André
Keyword(s):  
Star Formation ◽  
Formation Process ◽  
Strong Correlation ◽  
Molecular Clouds ◽  
Spatial Distributions ◽  
Complete Sample ◽  
Physical Mechanisms ◽  
Prestellar Cores ◽  
Formation And Evolution ◽  
Cloud Complex

AbstractOne of the main scientific goals of the Herschel Gould Belt survey is to elucidate the physical mechanisms responsible for the formation and evolution of prestellar cores in molecular clouds. In the ~11 deg2 field of Aquila imaged with Herschel/PACS-SPIRE at 70–500 μm, we have identified a complete sample of 651 starless cores, 446 of them are gravitationally-bound candidate prestellar cores. Our Herschel observations also provide an unprecedented census of filaments in the Aquila cloud and suggest an intimate connection between these filaments and the formation process of prestellar cores. Indeed, a strong correlation is found between their spatial distributions. These Herschel findings support a filamentary paradigm for the early stages of star formation, where the cores result from the gravitational fragmentation of the densest filaments.

scholarly journals Small-Scale Structure of the Mon R2 Cloud Core

1994 ◽  
Vol 140 ◽  
pp. 266-267
Author(s):  
TH. Henning ◽  
R. Chini ◽  
W. Pfau
Keyword(s):  
Star Formation ◽  
High Resolution ◽  
Formation Process ◽  
Molecular Clouds ◽  
Scale Structure ◽  
Small Scale ◽  
Small Scale Structure ◽  
Ir Sources ◽  
Cloud Core

High-resolution mm continuum observations are especially well suited to detect clumpy structures in molecular clouds. In this paper we concentrate on the Mon R2 cloud core which is associated with a cluster of IR sources. Walker et al. (1990) made a 1.3 mm map with 30″ resolution. They found an unresolved and elongated structure extending from NE to SW. Here, we discuss high-resolution continuum maps at 870 and 1300 µm showing a rich clumpy structure on the scale of several 10 arcsec. The clumps are probably intimately linked to the star formation process in Mon R2.

scholarly journals Deeply Embedded Protostellar Population in the Central Molecular Zone Suggested by H2O Masers and Dense Cores

2016 ◽  
Vol 11 (S322) ◽  
pp. 99-102
Author(s):  
Xing Lu ◽  
Qizhou Zhang ◽  
Jens Kauffmann ◽  
Thushara Pillai ◽  
Steven N. Longmore ◽  
...  
Keyword(s):  
Star Formation ◽  
Dust Emission ◽  
High Sensitivity ◽  
High Angular Resolution ◽  
Physical Conditions ◽  
Dense Cores ◽  
The Galaxy ◽  
Water Masers ◽  
Water Maser

AbstractThe Central Molecular Zone (CMZ), usually referring to the inner 500 pc of the Galaxy, contains a dozen of massive (~105M⊙) molecular clouds. Are these clouds going to actively form stars like Sgr B2? How are they affected by the extreme physical conditions in the CMZ, such as strong turbulence? Here we present a first step towards answering these questions. Using high-sensitivity, high angular resolution radio and (sub)millimeter observations, we studied deeply embedded star formation in six massive clouds in the CMZ, including the 20 and 50 km s−1 clouds, Sgr B1 off (as known as dust ridge clouds e/f), Sgr C, Sgr D, and G0.253 – 0.016. The VLA water maser observations suggest a population of deeply embedded protostellar candidates, many of which are new detections. The SMA 1.3 mm continuum observations reveal peaks in dust emission associated with the masers, suggesting the existence of dense cores. While our findings confirm that clouds such as G0.253 – 0.016 lack internal compact substructures and are quiescent in terms of star formation, two clouds (the 20 km s−1 cloud and Sgr C) stand out with clusters of water masers with associated dense cores which may suggest a population of deeply embedded protostars at early evolutionary phases. Follow-up observations with VLA and ALMA are necessary to confirm their protostellar nature.

scholarly journals Formation of Giant Molecular Clouds by Coagulation of Small Molecular Clouds in a Spiral Gravitational Potential

1987 ◽  
Vol 115 ◽  
pp. 541-543
Author(s):  
Kohji Tomisaka
Keyword(s):  
Star Formation ◽  
Time Evolution ◽  
Gravitational Potential ◽  
Formation Process ◽  
Molecular Clouds ◽  
Spiral Structure ◽  
Giant Molecular Clouds ◽  
Short Lifetime ◽  
Spiral Arm

The formation process of giant molecular clouds (GMCs) is investigated from the standpoint of the coagulation theory of molecular clouds. Small clouds collide with each other and grow to become massive ones. Ultimately they form GMCs with a finite lifetime. The occurrence of star formation in a GMC destroys it and consequently small clouds are formed again. We study the time evolution of the clouds which move through a spiral gravitational potential by an N-body simulation. Then the ensemble of clouds responds to the spiral potential and forms a spiral structure similar to that produced by hydrodynamical galactic shock. It is shown that GMCs are formed in the spiral arm region by collisions between clouds. The distribution of GMCs indicates their short lifetime, of the order of a few times 107 years.

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 Two-Dimensional Radiation-Hydrodynamics Calculations of the Formation of 0-B Associations in Dense Molecular Clouds

1980 ◽  
Vol 58 ◽  
pp. 275-282
Author(s):  
Richard I. Klein ◽  
Maxwell T. Sandford II ◽  
Rodney W. Whitaker
Keyword(s):  
Star Formation ◽  
Formation Process ◽  
Molecular Cloud ◽  
Molecular Clouds ◽  
Radiation Hydrodynamics ◽  
Combined Effects ◽  
Two Dimensional ◽  
Density Enhancement

AbstractTwo-dimensional calculations of ionization-shockwave propagation into a curved molecular cloud are presented. Density enhancement occurs due to the combined effects of cloud curvature and radiation flow. The star formation process is expected to be enhanced near the edges of irregularly shaped molecular clouds.

scholarly journals Spectral shifting strongly constrains molecular cloud disruption by radiation pressure on dust

2018 ◽  
Vol 611 ◽  
pp. A70 ◽  
Author(s):  
Stefan Reissl ◽  
Ralf S. Klessen ◽  
Mordecai-Mark Mac Low ◽  
Eric W. Pellegrini
Keyword(s):  
Star Formation ◽  
Radiation Pressure ◽  
Formation Process ◽  
Molecular Clouds ◽  
Far Infrared ◽  
Young Star ◽  
Star Forming ◽  
Grain Sizes ◽  
Single Temperature ◽  
Spectral Shifting

Aim. We aim to test the hypothesis that radiation pressure from young star clusters acting on dust is the dominant feedback agent disrupting the largest star-forming molecular clouds and thus regulating the star-formation process.Methods. We performed multi-frequency, 3D, radiative transfer calculations including both scattering and absorption and re-emission to longer wavelengths for model clouds with masses of 104–107 M⊙, containing embedded clusters with star formation efficiencies of 0.009–91%, and varying maximum grain sizes up to 200 μm. We calculated the ratio between radiative and gravitational forces to determine whether radiation pressure can disrupt clouds.Results. We find that radiation pressure acting on dust almost never disrupts star-forming clouds. Ultraviolet and optical photons from young stars to which the cloud is optically thick do not scatter much. Instead, they quickly get absorbed and re-emitted by the dust at thermal wavelengths. As the cloud is typically optically thin to far-infrared radiation, it promptly escapes, depositing little momentum in the cloud. The resulting spectrum is more narrowly peaked than the corresponding Planck function, and exhibits an extended tail at longer wavelengths. As the opacity drops significantly across the sub-mm and mm wavelength regime, the resulting radiative force is even smaller than for the corresponding single-temperature blackbody. We find that the force from radiation pressure falls below the strength of gravitational attraction by an order of magnitude or more for either Milky Way or moderate starbust conditions. Only for unrealistically large maximum grain sizes, and star formation efficiencies far exceeding 50% do we find that the strength of radiation pressure can exceed gravity.Conclusions. We conclude that radiation pressure acting on dust does not disrupt star-forming molecular clouds in any Local Group galaxies. Radiation pressure thus appears unlikely to regulate the star-formation process on either local or global scales.

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