scholarly journals A survey of molecular cores in M 17 SWex

2019 ◽  
Author(s):  
Tomomi Shimoikura ◽  
Kazuhito Dobashi ◽  
Asha Hirose ◽  
Fumitaka Nakamura ◽  
Yoshito Shimajiri ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Massive Star ◽  
Near Infrared ◽  
Young Stellar Objects ◽  
High Mass ◽  
Physical Parameters ◽  
Massive Star Formation ◽  
Dark Cloud ◽  
The Magnetic Field

Abstract A survey of molecular cores covering the infrared dark cloud known as the M 17 southwest extension (M 17 SWex) has been carried out with the 45 m Nobeyama Radio Telescope. Based on the N2H+ (J = 1–0) data obtained, we have identified 46 individual cores whose masses are in the range from 43 to $3026\, {M}_{\odot }$. We examined the relationship between the physical parameters of the cores and those of young stellar objects (YSOs) associated with the cores found in the literature. The comparison of the virial mass and the core mass indicates that most of the cores can be gravitationally stable if we assume a large external pressure. Among the 46 cores, we found four massive cores with YSOs. They have large masses of $\gtrsim 1000\, M_{\odot }$ and line widths of $\gtrsim 2.5\:$km s−1 which are similar to those of clumps forming high-mass stars. However, previous studies have shown that there is no active massive star formation in this region. Recent measurements of near-infrared polarization imply that the magnetic field around M 17 SWex is likely to be strong enough to support the cores against self-gravity. We therefore suggest that the magnetic field may prevent the cores from collapsing, causing the low level of massive star formation in M 17 SWex.

scholarly journals Herschel-HOBYS study of the earliest phases of high-mass star formation in NGC 6357

2019 ◽  
Vol 625 ◽  
pp. A134 ◽  
Author(s):  
D. Russeil ◽  
M. Figueira ◽  
A. Zavagno ◽  
F. Motte ◽  
N. Schneider ◽  
...  
Keyword(s):  
Star Formation ◽  
Formation Process ◽  
Massive Star ◽  
Spectral Energy Distribution ◽  
High Mass ◽  
Physical Parameters ◽  
Evolutionary Status ◽  
Mass Star ◽  
Massive Star Formation ◽  
Dense Cores

Aims. To constrain models of high-mass star formation it is important to identify the massive dense cores (MDCs) that are able to form high-mass star(s). This is one of the purposes of the Herschel/HOBYS key programme. Here, we carry out the census and characterise of the properties of the MDCs population of the NGC 6357 H II region. Methods. Our study is based on the Herschel/PACS and SPIRE 70−500 μm images of NGC 6357 complemented with (sub-)millimetre and mid-infrared data. We followed the procedure established by the Herschel/HOBYS consortium to extract ~0.1 pc massive dense cores using the getsources software. We estimated their physical parameters (temperatures, masses, luminosities) from spectral energy distribution (SED) fitting. Results. We obtain a complete census of 23 massive dense cores, amongst which one is found to be IR-quiet and twelve are starless, representing very early stages of the star-formation process. Focussing on the starless MDCs, we have considered their evolutionary status, and suggest that only five of them are likely to form a high-mass star. Conclusions. We find that, contrarily to the case in NGC 6334, the NGC 6357 region does not exhibit any ridge or hub features that are believed to be crucial to the massive star formation process. This study adds support for an empirical model in which massive dense cores and protostars simultaneously accrete mass from the surrounding filaments. In addition, the massive star formation in NGC 6357 seems to have stopped and the hottest stars in Pismis 24 have disrupted the filaments.

scholarly journals Zeeman splitting of OH masers and the galactic magnetic field

2002 ◽  
Vol 206 ◽  
pp. 371-374 ◽  
Author(s):  
Vincent L. Fish ◽  
Mark J. Reid ◽  
Alice L. Argon ◽  
Karl M. Menten
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Large Scale ◽  
Massive Star ◽  
Milky Way ◽  
Zeeman Splitting ◽  
Galactic Magnetic Field ◽  
Massive Star Formation ◽  
The Magnetic Field

Zeeman measurements of OH masers are used to probe the magnetic field around regions of massive star formation. Previous observations suggested that OH maser field directions were aligned in a clockwise sense in the Milky Way, but recent data from a large-scale VLA survey do not support this hypothesis. However, these observations suggest that the magnetic field of the Milky Way is correlated on kiloparsec scales.

scholarly journals Rapid and efficient mass collection by a supersonic cloud–cloud collision as a major mechanism of high-mass star formation

2020 ◽  
Author(s):  
Yasuo Fukui ◽  
Tsuyoshi Inoue ◽  
Takahiro Hayakawa ◽  
Kazufumi Torii
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Gravitational Instability ◽  
Mass Function ◽  
Initial Mass Function ◽  
High Mass ◽  
Mass Star ◽  
Major Mechanism ◽  
Dense Cores ◽  
The Magnetic Field

Abstract A supersonic cloud–cloud collision produces a shock-compressed layer which leads to formation of high-mass stars via gravitational instability. We carried out a detailed analysis of the layer by using the numerical simulations of magneto-hydrodynamics which deal with colliding molecular flows at a relative velocity of 20 km s−1 (Inoue & Fukui 2013, ApJ, 774, L31). Maximum density in the layer increases from 1000 cm−3 to more than 105 cm−3 within 0.3 Myr by compression, and the turbulence and the magnetic field in the layer are amplified by a factor of ∼5, increasing the mass accretion rate by two orders of magnitude to more than 10−4 $ M_{\odot } $ yr−1. The layer becomes highly filamentary due to gas flows along the magnetic field lines, and dense cores are formed in the filaments. The massive dense cores have size and mass of 0.03–0.08 pc and 8–$ 50\, M_{\odot } $ and they are usually gravitationally unstable. The mass function of the dense cores is significantly top-heavy as compared with the universal initial mass function, indicating that the cloud–cloud collision preferentially triggers the formation of O and early B stars. We argue that the cloud–cloud collision is a versatile mechanism which creates a variety of stellar clusters from a single O star like RCW 120 and M 20 to tens of O stars of a super star cluster like RCW 38 and a mini-starburst W 43. The core mass function predicted by the present model is consistent with the massive dense cores obtained by recent ALMA observations in RCW 38 (Torii et al. 2021, PASJ, in press) and W 43 (Motte et al. 2018, Nature Astron., 2, 478). Considering the increasing evidence for collision-triggered high-mass star formation, we argue that cloud–cloud collision is a major mechanism of high-mass star formation.

scholarly journals Molecular environs and triggered star formation around the large Galactic infrared bubble N 24

2019 ◽  
Vol 487 (2) ◽  
pp. 1517-1528 ◽  
Author(s):  
Xu Li ◽  
Jarken Esimbek ◽  
Jianjun Zhou ◽  
W A Baan ◽  
Weiguang Ji ◽  
...  
Keyword(s):  
Star Formation ◽  
Massive Star ◽  
Young Stellar Objects ◽  
Collapse Mechanism ◽  
Kinetic Temperature ◽  
H Ii Regions ◽  
Dark Cloud ◽  
Stellar Objects ◽  
Multi Wavelength ◽  
Mass Size

Abstract A multi-wavelength analysis of the large Galactic infrared bubble N 24 is presented in this paper in order to investigate the molecular and star-formation environment around expanding H ii regions. Using archival data from Herschel and ATLASGAL, the distribution and physical properties of the dust over the entire bubble are studied. Using the Clumpfind2d algorithm, 23 dense clumps are identified, with sizes and masses in the range 0.65–1.73 pc and 600–16 300 M⊙, respectively. To analyse the molecular environment in N 24, observations of NH3 (1,1) and (2,2) were carried out using the Nanshan 26-m radio telescope. Analysis of the kinetic temperature and gravitational stability of these clumps suggests gravitational collapse in several of them. The mass–size distributions of the clumps and the presence of massive young protostars indicate that the shell of N 24 is a region of ongoing massive-star formation. The compatibility of the dynamical and fragmentation timescales and the overabundance of young stellar objects and clumps on the rim suggest that the ‘collect-and-collapse’ mechanism is in play at the boundary of the bubble, but the existence of the infrared dark cloud at the edge of bubble indicates that a ‘radiation-driven implosion’ mechanism may also have played a role there.

scholarly journals Magnetic fields at the onset of high-mass star formation

2018 ◽  
Vol 614 ◽  
pp. A64 ◽  
Author(s):  
H. Beuther ◽  
J. D. Soler ◽  
W. Vlemmings ◽  
H. Linz ◽  
Th. Henning ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Magnetic Fields ◽  
Spectral Line ◽  
Function Analysis ◽  
High Mass ◽  
Mass Star ◽  
Starting Point ◽  
Polarized Emission ◽  
The Magnetic Field

Context. The importance of magnetic fields at the onset of star formation related to the early fragmentation and collapse processes is largely unexplored today. Aims. We want to understand the magnetic field properties at the earliest evolutionary stages of high-mass star formation. Methods. The Atacama Large Millimeter Array is used at 1.3 mm wavelength in full polarization mode to study the polarized emission, and, using this, the magnetic field morphologies and strengths of the high-mass starless region IRDC 18310-4. Results. Polarized emission is clearly detected in four sub-cores of the region; in general it shows a smooth distribution, also along elongated cores. Estimating the magnetic field strength via the Davis-Chandrasekhar-Fermi method and following a structure function analysis, we find comparably large magnetic field strengths between ~0.3–5.3 mG. Comparing the data to spectral line observations, the turbulent-to-magnetic energy ratio is low, indicating that turbulence does not significantly contribute to the stability of the gas clump. A mass-to-flux ratio around the critical value 1.0 – depending on column density – indicates that the region starts to collapse, which is consistent with the previous spectral line analysis of the region. Conclusions. While this high-mass region is collapsing and thus at the verge of star formation, the high magnetic field values and the smooth spatial structure indicate that the magnetic field is important for the fragmentation and collapse process. This single case study can only be the starting point for larger sample studies of magnetic fields at the onset of star formation.

scholarly journals A Study of Magnetic Fields on Bright-Rimmed Clouds

2015 ◽  
Vol 11 (S315) ◽  
Author(s):  
Takayoshi Kusune ◽  
Koji Sugitani
Keyword(s):  
Magnetic Field ◽  
Massive Star ◽  
Near Infrared ◽  
Polarization Vector ◽  
Field Configuration ◽  
Magnetic Field Direction ◽  
Magnetic Field Configuration ◽  
Gas Compression ◽  
Imaging Polarimetry ◽  
The Magnetic Field

AbstractWe have made near-infrared (JHKs) imaging polarimetry toward 24 bright-rimmed clouds in the southern hemisphere in order to reveal their magnetic field structures. The obtained polarization vector maps show that the magnetic field directions inside the bright rim are different from its ambient magnetic field direction, implying that magnetic field structures just inside the ionized front of the clouds are due to the gas compression by UV radiation from nearby massive star. Our investigation into the relation between the magnetic field configuration and the shape of the cloud suggests that the magnetic field configuration affects the evolution of the cloud shape.

scholarly journals EARLY PHASE OF MASSIVE STAR FORMATION: A CASE STUDY OF THE INFRARED DARK CLOUD G084.81–01.09

2011 ◽  
Vol 193 (1) ◽  
pp. 10 ◽  
Author(s):  
S. B. Zhang ◽  
J. Yang ◽  
Y. Xu ◽  
J. D. Pandian ◽  
K. M. Menten ◽  
...  
Keyword(s):  
Star Formation ◽  
Early Phase ◽  
Massive Star ◽  
Massive Star Formation ◽  
Dark Cloud

scholarly journals Magnetic Fields in Dark Cloud Cores and H2O Masers

1990 ◽  
Vol 140 ◽  
pp. 305-308
Author(s):  
Rolf Güsten ◽  
Dirk Fiebig
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Field Strength ◽  
Kinetic Temperature ◽  
Dark Cloud ◽  
Dense Cores ◽  
Low Mass ◽  
Cloud Cores ◽  
First Time ◽  
The Magnetic Field

We present results of recent circular polarization experiments with the MPIfR 100-m telescope, revealing for the first time, the magnetic field strength towards interstellar H2O masers and the dense cores of local dark cloud complexes. Weak Zeeman splittings of a few 10 kHz only in the 22.235 GHz maser transition of the non-paramagnetic H2O molecule imply magnetic field strengths of ~ 50 mG in the dense (n ~ 1010 cm−3) masing layer. With the recently identified CCS radical it became possible to study the magnetic field associated with dense (~ 105 cm−3) dark cloud cores, the potential sites of future star formation. We report the detection of a −110μG field towards TMC-1C, a low-mass core associated with the Taurus Molecular Cloud. From complementary gas density and kinetic temperature probing measurements, we derive approximate equipartition between magnetic, gravitational and thermal energy for this clump.

scholarly journals A MERLIN study of 6 GHz excited OH & 6.7 GHz methanol masers in ON1

2007 ◽  
Vol 3 (S242) ◽  
pp. 188-189
Author(s):  
James A. Green ◽  
A. M. S. Richards ◽  
H. Flood ◽  
W. H. T. Vlemmings ◽  
R. J. Cohen
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Cross Correlation ◽  
Massive Star ◽  
Zeeman Splitting ◽  
Massive Star Formation ◽  
Star Formation Region ◽  
Formation Region ◽  
Methanol Masers ◽  
Field Strengths

AbstractMERLIN observations of 6.668-GHz Methanol and 6.035-GHz OH emission from the known massive star-formation region ON1 are presented. Maser components are found to lie at the southern edge of the UCHII with consistent polarization angles across the strongest features. Zeeman splitting of OH shows magnetic field strengths between +0.4 to −5.3 mG and from cross-correlation a tentative methanol magnetic field of −18mG is detected.

scholarly journals The molecular cloud and embedded young stellar population associated with IRAS 18236–1205

2009 ◽  
Vol 5 (S266) ◽  
pp. 516-516
Author(s):  
Ricardo Retes ◽  
Abraham Luna ◽  
Divakara Mayya ◽  
Luis Carrasco
Keyword(s):  
Star Formation ◽  
Molecular Cloud ◽  
Massive Star ◽  
Stellar Population ◽  
Spectral Energy Distribution ◽  
Point Sources ◽  
Young Stellar Objects ◽  
Spectral Energy ◽  
Massive Star Formation ◽  
Iras Source

AbstractWe test a membership method to select embedded young stellar objects (YSOs) from a Galactic molecular cloud with ongoing massive star formation using multiband analysis. We select and discuss the embedded stellar population in the molecular cloud associated with IRAS 18235−1205, a small, geometrically well-defined Galactic molecular cloud. The IRAS source has infrared fluxes characteristic of an UCHii region, CS(J = 2 − 1) emission, and methanol and water maser emission, suggesting that this region is a good candidate for studies of young, massive star formation. The selection method of embedded stellar populations is based on the spatial distribution of 13CO(J = 1 − 0) and Spitzer/MIPS 24 μm point sources. Photometric analysis using near/mid-infrared images are used to test our selection criteria. Three objects are associated with the IRAS source; two have a characteristic spectral-energy distribution (SED) of a Class I/0 object (protostar) and the third has an SED of Class II.

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