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 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 Formation of Stellar Clusters and the Importance of Thermodynamics for Fragmentation

2007 ◽  
Vol 3 (S246) ◽  
pp. 3-12
Author(s):  
Ralf S. Klessen ◽  
Paul C. Clark ◽  
Simon C. O. Glover
Keyword(s):  
Star Formation ◽  
Dynamic Properties ◽  
Mass Function ◽  
Mass Scale ◽  
Initial Mass Function ◽  
Solar Neighborhood ◽  
High Mass ◽  
Mass Star ◽  
Heating Regime ◽  
Effective Equation

AbstractWe discuss results from numerical simulations of star cluster formation in the turbulent interstellar medium (ISM). The thermodynamic behavior of the star-forming gas plays a crucial role in fragmentation and determines the stellar mass function as well as the dynamic properties of the nascent stellar cluster. This holds for star formation in molecular clouds in the solar neighborhood as well as for the formation of the very first stars in the early universe. The thermodynamic state of the ISM is a result of the balance between heating and cooling processes, which in turn are determined by atomic and molecular physics and by chemical abundances. Features in the effective equation of state of the gas, such as a transition from a cooling to a heating regime, define a characteristic mass scale for fragmentation and so set the peak of the initial mass function of stars (IMF). As it is based on fundamental physical quantities and constants, this is an attractive approach to explain the apparent universality of the IMF in the solar neighborhood as well as the transition from purely primordial high-mass star formation to the more normal low-mass mode observed today.

scholarly journals HIGH-MASS STAR FORMATION IN NORMAL LATE-TYPE GALAXIES: OBSERVATIONAL CONSTRAINTS TO THE INITIAL MASS FUNCTION

2009 ◽  
Vol 706 (2) ◽  
pp. 1527-1544 ◽  
Author(s):  
A. Boselli ◽  
S. Boissier ◽  
L. Cortese ◽  
V. Buat ◽  
T. M. Hughes ◽  
...  
Keyword(s):  
Star Formation ◽  
Mass Function ◽  
Initial Mass Function ◽  
High Mass ◽  
Initial Mass ◽  
Observational Constraints ◽  
Mass Star ◽  
Late Type

scholarly journals Dense cores and star formation in the giant molecular cloud Vela C

2019 ◽  
Vol 628 ◽  
pp. A110 ◽  
Author(s):  
F. Massi ◽  
A. Weiss ◽  
D. Elia ◽  
T. Csengeri ◽  
E. Schisano ◽  
...  
Keyword(s):  
Star Formation ◽  
Molecular Cloud ◽  
Galactic Plane ◽  
Mass Function ◽  
Initial Mass Function ◽  
High Mass ◽  
Mass Star ◽  
Ancillary Data ◽  
Core Mass ◽  
Giant Molecular Cloud

Context. The Vela Molecular Ridge is one of the nearest (700 pc) giant molecular cloud (GMC) complexes hosting intermediate-mass (up to early B, late O stars) star formation, and is located in the outer Galaxy, inside the Galactic plane. Vela C is one of the GMCs making up the Vela Molecular Ridge, and exhibits both sub-regions of robust and sub-regions of more quiescent star formation activity, with both low- and intermediate(high)-mass star formation in progress. Aims. We aim to study the individual and global properties of dense dust cores in Vela C, and aim to search for spatial variations in these properties which could be related to different environmental properties and/or evolutionary stages in the various sub-regions of Vela C. Methods. We mapped the submillimetre (345 GHz) emission from vela C with LABOCA (beam size ~19′′2, spatial resolution ~0.07 pc at 700 pc) at the APEX telescope. We used the clump-finding algorithm CuTEx to identify the compact submillimetre sources. We also used SIMBA (250 GHz) observations, and Herschel and WISE ancillary data. The association with WISE red sources allowed the protostellar and starless cores to be separated, whereas the Herschel dataset allowed the dust temperature to be derived for a fraction of cores. The protostellar and starless core mass functions (CMFs) were constructed following two different approaches, achieving a mass completeness limit of 3.7 M⊙. Results. We retrieved 549 submillimetre cores, 316 of which are starless and mostly gravitationally bound (therefore prestellar in nature). Both the protostellar and the starless CMFs are consistent with the shape of a Salpeter initial mass function in the high-mass part of the distribution. Clustering of cores at scales of 1–6 pc is also found, hinting at fractionation of magnetised, turbulent gas.

Revealing magnetic fields towards massive protostars: a multi-scale approach using masers and dust

2018 ◽  
Vol 14 (A30) ◽  
pp. 111-112
Author(s):  
Daria Dall’Olio ◽  
W. H. T. Vlemmings ◽  
M. V. Persson
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Magnetic Fields ◽  
Spatial Scales ◽  
High Mass ◽  
Small Scale ◽  
Evolutionary Stage ◽  
Mass Star ◽  
Filamentary Structure ◽  
The Magnetic Field

AbstractMagnetic fields play a significant role during star formation processes, hindering the fragmentation and the collapse of the parental cloud, and affecting the accretion mechanisms and feedback phenomena. However, several questions still need to be addressed to clarify the importance of magnetic fields at the onset of high-mass star formation, such as how strong they are and at what evolutionary stage and spatial scales their action becomes relevant. Furthermore, the magnetic field parameters are still poorly constrained especially at small scales, i.e. few astronomical units from the central object, where the accretion disc and the base of the outflow are located. Thus we need to probe magnetic fields at different scales, at different evolutionary steps and possibly with different tracers. We show that the magnetic field morphology around high-mass protostars can be successfully traced at different scales by observing maser and dust polarised emission. A confirmation that they are effective tools is indeed provided by our recent results from 6.7 GHz MERLIN observations of the massive protostar IRAS 18089-1732, where we find that the small-scale magnetic field probed by methanol masers is consistent with the large-scale magnetic field probed by dust (Dall’Olio et al. 2017 A&A 607, A111). Moreover we present results obtained from our ALMA Band 7 polarisation observations of G9.62+0.20, which is a massive star-forming region with a sequence of cores at different evolutionary stages (Dall’Olio et al. submitted to A&A). In this region we resolve several protostellar cores embedded in a bright and dusty filamentary structure. The magnetic field morphology and strength in different cores is related to the evolutionary sequence of the star formation process which is occurring across the filament.

scholarly journals Unifying low- and high-mass star formation through density-amplified hubs of filaments

2020 ◽  
Vol 642 ◽  
pp. A87 ◽  
Author(s):  
M. S. N. Kumar ◽  
P. Palmeirim ◽  
D. Arzoumanian ◽  
S. I. Inutsuka
Keyword(s):  
Star Formation ◽  
Massive Stars ◽  
Radial Profile ◽  
Beam Width ◽  
Mass Function ◽  
Initial Mass Function ◽  
High Mass ◽  
Mass Star ◽  
Giant Molecular Clouds ◽  
Stellar Sources

Context. Star formation takes place in giant molecular clouds, resulting in mass-segregated young stellar clusters composed of Sun-like stars, brown dwarfs, and massive O-type(50–100 M⊙) stars. Aims. We aim to identify candidate hub-filament systems (HFSs) in the Milky Way and examine their role in the formation of the highest mass stars and star clusters. Methods. The Herschel survey HiGAL has catalogued about 105 clumps. Of these, approximately 35 000 targets are detected at the 3σ level in a minimum of four bands. Using the DisPerSE algorithm we detect filamentary skeletons on 10′ × 10′ cut-outs of the SPIRE 250 μm images (18′′ beam width) of the targets. Any filament with a total length of at least 55′′ (3 × 18′′) and at least 18′′ inside the clump was considered to form a junction at the clump. A hub is defined as a junction of three or more filaments. Column density maps were masked by the filament skeletons and averaged for HFS and non-HFS samples to compute the radial profile along the filaments into the clumps. Results. Approximately 3700 (11%) are candidate HFSs, of which about 2150 (60%) are pre-stellar and 1400 (40%) are proto-stellar. The filaments constituting the HFSs have a mean length of ~10–20 pc, a mass of ~5 × 104 M⊙, and line masses (M∕L) of ~2 × 103 M⊙ pc−1. All clumps with L > 104 L⊙ and L > 105 L⊙ at distances within 2 and 5 kpc respectively are located in the hubs of HFSs. The column densities of hubs are found to be enhanced by a factor of approximately two (pre-stellar sources) up to about ten (proto-stellar sources). Conclusions. All high-mass stars preferentially form in the density-enhanced hubs of HFSs. This amplification can drive the observed longitudinal flows along filaments providing further mass accretion. Radiation pressure and feedback can escape into the inter-filamentary voids. We propose a “filaments to clusters” unified paradigm for star formation, with the following salient features: (a) low-intermediate-mass stars form slowly (106 yr) in the filaments and massive stars form quickly (105 yr) in the hub, (b) the initial mass function is the sum of stars continuously created in the HFS with all massive stars formed in the hub, (c) feedback dissipation and mass segregation arise naturally due to HFS properties, and explain the (d) age spreads within bound clusters and the formation of isolated OB associations.

scholarly journals Outflows, cores, and magnetic field orientations in W43-MM1 as seen by ALMA

2020 ◽  
Vol 640 ◽  
pp. A111
Author(s):  
C. Arce-Tord ◽  
F. Louvet ◽  
P. C. Cortes ◽  
F. Motte ◽  
C. L. H. Hull ◽  
...  
Keyword(s):  
Magnetic Field ◽  
High Mass ◽  
Continuum Emission ◽  
High Angular Resolution ◽  
Mass Star ◽  
Star Forming ◽  
The Core ◽  
Dense Cores ◽  
The Impact ◽  
The Magnetic Field

Aims. It has been proposed that the magnetic field, which is pervasive in the interstellar medium, plays an important role in the process of massive star formation. To better understand the impact of the magnetic field at the pre- and protostellar stages, high-angular resolution observations of polarized dust emission toward a large sample of massive dense cores are needed. We aim to reveal any correlation between the magnetic field orientation and the orientation of the cores and outflows in a sample of protostellar dense cores in the W43-MM1 high-mass star-forming region. Methods. We used the Atacama Large Millimeter Array in Band 6 (1.3 mm) in full polarization mode to map the polarized emission from dust grains at a physical scale of ~2700 au. We used these data to measure the orientation of the magnetic field at the core scale. Then, we examined the relative orientations of the core-scale magnetic field, of the protostellar outflows, and of the major axis of the dense cores determined from a 2D Gaussian fit in the continuum emission. Results. We find that the orientation of the dense cores is not random with respect to the magnetic field. Instead, the dense cores are compatible with being oriented 20–50° with respect to the magnetic field. As for the outflows, they could be oriented 50–70° with respect to the magnetic field, or randomly oriented with respect to the magnetic field, which is similar to current results in low-mass star-forming regions. Conclusions. The observed alignment of the position angle of the cores with respect to the magnetic field lines shows that the magnetic field is well coupled with the dense material; however, the 20–50° preferential orientation contradicts the predictions of the magnetically-controlled core-collapse models. The potential correlation of the outflow directions with respect to the magnetic field suggests that, in some cases, the magnetic field is strong enough to control the angular momentum distribution from the core scale down to the inner part of the circumstellar disks where outflows are triggered.

scholarly journals Star Formation in Cooling Flows

1992 ◽  
Vol 45 (4) ◽  
pp. 501
Author(s):  
PEJ Nulsen
Keyword(s):  
Star Formation ◽  
Mass Function ◽  
Good Evidence ◽  
Initial Mass Function ◽  
High Mass ◽  
Mass Star ◽  
Cooling Flows ◽  
Cooling Flow ◽  
The Masses ◽  
Intracluster Gas

There is good evidence that the intracluster gas near the centres of many clusters of galaxies is cooling over at least a decade in temperature. This results in an inflow, which is approximately steady where the cooling time of the gas is shorter than the age of the flow. X-ray observations indicate that the cooling gas must have substantial inhomogeneities. Non-linear development of thermal instability causes cooled gas clouds to be deposited throughout the region of the steady cooling flow. The masses of these clouds will be small, typically a lot less than a Jeans mass when they first form. It is argued that the difficulty of forming large clouds in the bulk of a cooling flow inhibits high mass star formation there. There is evidence of some 'normal' star formation near to the centres of many cooling flows where conditions are more favourable for the formation of giant clouds. The initial mass function is strongly affected by the star formation environment in cooling flows.

scholarly journals Gravity and Rotation Drag the Magnetic Field in High-mass Star Formation

2020 ◽  
Vol 904 (2) ◽  
pp. 168
Author(s):  
Henrik Beuther ◽  
Juan D. Soler ◽  
Hendrik Linz ◽  
Thomas Henning ◽  
Caroline Gieser ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
High Mass ◽  
Mass Star ◽  
The Magnetic Field

Low‐Mass Star Formation and the Initial Mass Function in IC 348

1998 ◽  
Vol 508 (1) ◽  
pp. 347-369 ◽  
Author(s):  
K. L. Luhman ◽  
G. H. Rieke ◽  
C. J. Lada ◽  
E. A. Lada
Keyword(s):  
Star Formation ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Mass Star ◽  
Low Mass
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