scholarly journals Core and stellar mass functions in massive collapsing filaments

2019 ◽  
Vol 625 ◽  
pp. A82 ◽  
Author(s):  
Evangelia Ntormousi ◽  
Patrick Hennebelle
Keyword(s):  
Star Formation ◽  
Flux Ratio ◽  
Mass Function ◽  
Initial Mass Function ◽  
Core Stability ◽  
High Mass ◽  
Core Mass ◽  
Hydrodynamical Simulation ◽  
Core Selection ◽  
Mass Functions

Context. The connection between the prestellar core mass function (CMF) and the stellar initial mass function (IMF) lies at the heart of all star formation theories, but it is inherently observationally unreachable. Aims. In this paper we aim to elucidate the earliest phases of star formation with a series of high-resolution numerical simulations that include the formation of sinks from high-density clumps. In particular, we focus on the transition from cores to sink particles within a massive molecular filament, and work towards identifying the factors that determine the shape of the CMF and the IMF. Methods. We have compared the CMF and IMF between magnetized and unmagnetized simulations, and between different resolutions. In order to study the effect of core stability, we applied different selection criteria according to the virial parameter and the mass-to-flux ratio of the cores. Results. We find that, in all models, selecting cores based on their kinematic virial parameter tends to exclude collapsing objects, because they host high velocity dispersions. Selecting only the thermally unstable magnetized cores, we observe that their mass-to-flux ratio spans almost two orders of magnitude for a given mass. We also see that, when magnetic fields are included, the CMF peaks at higher core mass values with respect to a pure hydrodynamical simulation. Nonetheless, all models produce sink mass functions with a high-mass slope consistent with Salpeter. Finally, we examined the effects of resolution and find that, in these isothermal simulations, even models with very high dynamical range fail to converge in the mass function. Conclusions. Our main conclusion is that, although the resulting CMFs and IMFs have similar slopes in all simulations, the cores have slightly different sizes and kinematical properties when a magnetic field is included, and this affects their gravitational stability. Nonetheless, a core selection based on the mass-to-flux ratio is not enough to alter the shape of the CMF, if we do not take thermal stability into account. Finally, we conclude that extreme care should be given to resolution issues when studying sink formation with an isothermal equation of state, since with each increase in resolution, fragmentation continues to smaller scales in a self-similar way.

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.

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 Bimodal Star Formation and Remnant-Dominated Galactic Models

1987 ◽  
Vol 117 ◽  
pp. 413-413
Author(s):  
Richard B. Larson
Keyword(s):  
Star Formation ◽  
Formation Rate ◽  
Mass Function ◽  
Current Data ◽  
Initial Mass Function ◽  
Solar Neighborhood ◽  
Gas Content ◽  
High Mass ◽  
Stellar Content ◽  
Stellar Initial Mass Function

Current data on the luminosity function of nearby stars allow the possibility that the stellar initial mass function (IMF) is double-peaked and that the star formation rate (SFR) has decreased substantially with time. It is then possible to account for all of the unseen mass in the solar vicinity as stellar remnants. A model for the solar neighborhood has been constructed in which the IMF is bimodal, the SFR is constant for the low-mass mode and strongly decreasing for the high-mass mode, and the mass in remnants is equal to the column density of unseen matter; this model is found to be consistent with all of the available constraints on the evolution and stellar content of the solar neighborhood. In particular, the observed chemical evolution is satisfactorily reproduced without infall. The total SFR in the model decreases roughly with the 1.4 power of the gas content, which is more plausible than the nearly constant SFR required by models with a monotonic IMF.

scholarly journals The Turbulent ISM of Galaxies 10 Gyrs ago: Star Formation, Gas Accretion, and IMF

2010 ◽  
Vol 6 (S277) ◽  
pp. 150-153
Author(s):  
Loïc Le Tiran ◽  
Matthew D. Lehnert
Keyword(s):  
Star Formation ◽  
Mechanical Energy ◽  
Mass Function ◽  
Big Bang ◽  
Initial Mass Function ◽  
High Mass ◽  
Energy Output ◽  
Massive Galaxies ◽  
Photometric Measurements ◽  
Gas Accretion

AbstractThe utilization of integral-field spectroscopy has led us to a new understanding of the physical conditions in galaxies within the first few billion years after the Big Bang. In this proceedings, we analyze observations of ~50 massive galaxies as seen as they were 10 Gyrs ago using SINFONI from the ESO-VLT. We show that the large line width they exhibit can be explained by the intense mechanical energy output from the young stars. We also study the influence of cold gas accretion upon these galaxies: We show that an unrealistic amount of shocked gas would be needed in order to explain the Hα emission from these galaxies through shocks from gas accretion with velocity about the Hα line widths of these galaxies. We also use DEEP2 photometric measurements for a sub-sample of 10 of these galaxies to evaluate their ratio of Hα to FUV flux as a function of their Hα and R-band luminosity surface brightnesses. Our data suggests that perhaps their initial mass function (IMF) is flatter than Salpeter at the high mass end, as has been suggested recently for some local galaxies. It may be that high turbulence is responsible for skewing the IMF towards more massive stars as suggested by some theories of star-formation. Much work is however needed to accredit this hypothesis.

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 Blue galaxies: modelling nebular He ii emission in high redshift galaxies

2019 ◽  
Vol 491 (3) ◽  
pp. 4509-4522 ◽  
Author(s):  
Kirk S S Barrow
Keyword(s):  
Star Formation ◽  
Emission Line ◽  
High Redshift ◽  
Mass Function ◽  
Initial Mass Function ◽  
High Mass ◽  
Test Case ◽  
Good Test ◽  
Cosmological Simulations ◽  
Modelling Studies

ABSTRACT Using cosmological simulations to make useful, scientifically relevant emission line predictions is a relatively new and rapidly evolving field. However, nebular emission lines have been particularly challenging to model because they are extremely sensitive to the local photoionization balance, which can be driven by a spatially dispersed distribution of stars amidst an inhomogeneous absorbing medium of dust and gas. As such, several unmodelled mysteries in observed emission line patterns exist in the literature. For example, there is some question as to why He ii λ4686/H β ratios in observations of lower metallicity dwarf galaxies tend to be higher than model predictions. Since hydrodynamic cosmological simulations are best suited to this mass and metallicity regime, this question presents a good test case for the development of a robust emission line modelling pipeline. The pipeline described in this work can model a process that produces high He ii λ4686/H β ratios and eliminate some of the modelling discrepancy for ratios below 3 per cent without including AGNs, X-ray binaries, high mass binaries, or a top-heavy stellar initial mass function. These ratios are found to be more sensitive to the presence of 15 Myr or longer gaps in the star formation histories than to extraordinary ionization parameters or specific star formation rates. They also closely correspond to the WR phase of massive stars. In addition to the investigation into He ii λ4686/H β ratios, this work charts a general path forward for the next generation of nebular emission line modelling studies.

scholarly journals Core mass function: a comparison study between Orion A and other massive filamentary clouds.

2015 ◽  
Vol 11 (S315) ◽  
Author(s):  
Zhiyuan Ren ◽  
Di Li
Keyword(s):  
Mass Function ◽  
High Mass ◽  
Comparison Study ◽  
Core Mass ◽  
Similar Morphology ◽  
Dark Clouds ◽  
Power Law Index ◽  
Infrared Dark Clouds ◽  
Mass Functions ◽  
Measured Mass

AbstractAs a giant compact filamentary cloud, Orion A has a similar morphology with those more distant filaments in infrared dark clouds as revealed in Herschel surveys. We compared their core mass functions and found a similar power law index of N(>m)∝ m−1.0 for the high-mass end, which may possibly indicates a common case for massive filamentary clouds. We also show that the measured mass function for a certain cloud would largely depend on its distance, thus call for caution in interpreting individual measurements of CMF.

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 Star Formation and the Origin of Stellar Masses

1993 ◽  
Vol 137 ◽  
pp. 795-797
Author(s):  
Ph. Podsiadlowski ◽  
N.M. Price
Keyword(s):  
Star Formation ◽  
Simple Model ◽  
Stellar Evolution ◽  
Main Sequence ◽  
Asymptotic Form ◽  
Mass Function ◽  
Initial Mass Function ◽  
Mass Distributions ◽  
Stellar Masses ◽  
Mass Functions

AbstractWe present a new model to explain stellar mass distributions in different stellar environments. In our model, the protostar phase is terminated, when the protostellar core embedded in a molecular clump experiences a collision with another star or protostellar clump, which ejects the protostellar core from its parent clump. Such dynamical interactions are necessarily important, if stars preferentially form in dense clusters. We show that, in a simple model, the initial mass function approaches a simple, asymptotic form, which strongly resembles observed mass functions. The model has important consequences for star formation in different environments. We also discuss the implications of the model for our understanding of pre-main-sequence stellar evolution.

scholarly journals Statistical mass function of prestellar cores from the density distribution of their natal clouds

2020 ◽  
Vol 635 ◽  
pp. A88
Author(s):  
S. Donkov ◽  
T. V. Veltchev ◽  
Ph. Girichidis ◽  
R. S. Klessen
Keyword(s):  
Power Law ◽  
Molecular Clouds ◽  
Mass Density ◽  
Mass Function ◽  
Initial Mass Function ◽  
High Mass ◽  
Core Mass ◽  
Density Relationship ◽  
Prestellar Cores ◽  
Spherical Cloud

The mass function of clumps observed in molecular clouds raises interesting theoretical issues, especially in its relation to the stellar initial mass function (IMF). We propose a statistical model of the mass function of prestellar cores (CMF), formed in self-gravitating isothermal clouds at a given stage of their evolution. The latter is characterized by the mass-density probability distribution function (ρ-PDF), which is a power-law with slope q. The different molecular clouds are divided into ensembles according to the PDF slope and each ensemble is represented by a single spherical cloud. The cores are considered as elements of self-similar structure typical for fractal clouds and are modeled by spherical objects populating each cloud shell. Our model assumes relations between size, mass, and density of the statistical cores. Out of these, a core mass-density relationship ρ ∝ mx is derived where x = 1∕(1 + q). We find that q determines the existence or nonexistence of a threshold density for core collapse. The derived general CMF is a power law of slope − 1 while the CMF of gravitationally unstable cores has a slope (−1 + x∕2), comparable with the slopes of the high-mass part of the stellar IMF and of observational CMFs.

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