The influence of infall on the properties of protoplanetary discs

Context. The properties of protoplanetary discs determine the conditions for planet formation. In addition, planets can already form during the early stages of infall. Aims. We constrain physical quantities such as the mass, radius, lifetime, and gravitational stability of protoplanetary discs by studying their evolution from formation to dispersal. Methods. We perform a population synthesis of protoplanetary discs with a total of 50 000 simulations using a 1D vertically integrated viscous evolution code, studying a parameter space of final stellar mass from 0.05 to 5 M⊙. Each star-and-disc system is set up shortly after the formation of the protostar and fed by infalling material from the parent molecular cloud core. Initial conditions and infall locations are chosen based on the results from a radiation-hydrodynamic population synthesis of circumstellar discs. We also consider a different infall prescription based on a magnetohydrodynamic (MHD) collapse simulation in order to assess the influence of magnetic fields on disc formation. The duration of the infall phase is chosen to produce a stellar mass distribution in agreement with the observationally determined stellar initial mass function. Results. We find that protoplanetary discs are very massive early in their lives. When averaged over the entire stellar population, the discs have masses of ~0.3 and 0.1 M⊙ for systems based on hydrodynamic or MHD initial conditions, respectively. In systems characterised by a final stellar mass ~1 M⊙, we find disc masses of ~0.7 M⊙ for the “hydro” case and ~0.2 M⊙ for the “MHD” case at the end of the infall phase. Furthermore, the inferred total disc lifetimes are long, ≈5–7 Myr on average. This is despite our choice of a high value of 10−2 for the background viscosity α-parameter. In addition, we find that fragmentation is common in systems that are simulated using hydrodynamic cloud collapse, with more fragments of larger mass formed in more massive systems. In contrast, if disc formation is limited by magnetic fields, fragmentation may be suppressed entirely. Conclusions. Our work draws a picture quite different from the one often assumed in planet formation studies: protoplanetary discs are more massive and live longer. This means that more mass is available for planet formation. Additionally, when fragmentation occurs, it can affect the disc’s evolution by transporting large amounts of mass radially. We suggest that the early phases in the lives of protoplanetary discs should be included in studies of planet formation. Furthermore, the evolution of the central star, including its accretion history, should be taken into account when comparing theoretical predictions of disc lifetimes with observations.

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The importance of magnetic fields for the initial mass function of the first stars

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1926 ◽

2020 ◽

Vol 497 (1) ◽

pp. 336-351 ◽

Cited By ~ 3

Author(s):

Piyush Sharda ◽

Christoph Federrath ◽

Mark R Krumholz

Keyword(s):

Magnetic Fields ◽

Initial Conditions ◽

High Redshift ◽

Three Dimensional ◽

Mass Function ◽

Initial Mass Function ◽

Initial Mass ◽

Dynamo Theory ◽

First Stars ◽

High Redshift Galaxies

ABSTRACT Magnetic fields play an important role for the formation of stars in both local and high-redshift galaxies. Recent studies of dynamo amplification in the first dark matter haloes suggest that significant magnetic fields were likely present during the formation of the first stars in the Universe at redshifts of 15 and above. In this work, we study how these magnetic fields potentially impact the initial mass function (IMF) of the first stars. We perform 200 high-resolution, three-dimensional (3D), magnetohydrodynamic (MHD) simulations of the collapse of primordial clouds with different initial turbulent magnetic field strengths as predicted from turbulent dynamo theory in the early Universe, forming more than 1100 first stars in total. We detect a strong statistical signature of suppressed fragmentation in the presence of strong magnetic fields, leading to a dramatic reduction in the number of first stars with masses low enough that they might be expected to survive to the present-day. Additionally, strong fields shift the transition point where stars go from being mostly single to mostly multiple to higher masses. However, irrespective of the field strength, individual simulations are highly chaotic, show different levels of fragmentation and clustering, and the outcome depends on the exact realization of the turbulence in the primordial clouds. While these are still idealized simulations that do not start from cosmological initial conditions, our work shows that magnetic fields play a key role for the primordial IMF, potentially even more so than for the present-day IMF.

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Can magnetized turbulence set the mass scale of stars?

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1883 ◽

2020 ◽

Vol 496 (4) ◽

pp. 5072-5088 ◽

Cited By ~ 2

Author(s):

Dávid Guszejnov ◽

Michael Y Grudić ◽

Philip F Hopkins ◽

Stella S R Offner ◽

Claude-André Faucher-Giguère

Keyword(s):

Star Formation ◽

Scaling Laws ◽

Initial Conditions ◽

Mass Function ◽

Stellar Mass ◽

Mass Scale ◽

Initial Mass Function ◽

Mhd Turbulence ◽

Numerical Resolution ◽

Stellar Masses

ABSTRACT Understanding the evolution of self-gravitating, isothermal, magnetized gas is crucial for star formation, as these physical processes have been postulated to set the initial mass function (IMF). We present a suite of isothermal magnetohydrodynamic (MHD) simulations using the gizmo code that follow the formation of individual stars in giant molecular clouds (GMCs), spanning a range of Mach numbers found in observed GMCs ($\mathcal {M} \sim 10\!-\!50$). As in past works, the mean and median stellar masses are sensitive to numerical resolution, because they are sensitive to low-mass stars that contribute a vanishing fraction of the overall stellar mass. The mass-weighted median stellar mass M50 becomes insensitive to resolution once turbulent fragmentation is well resolved. Without imposing Larson-like scaling laws, our simulations find $M_\mathrm{50} \,\, \buildrel\propto \over \sim \,\,M_\mathrm{0} \mathcal {M}^{-3} \alpha _\mathrm{turb}\, \mathrm{SFE}^{1/3}$ for GMC mass M0, sonic Mach number $\mathcal {M}$, virial parameter αturb, and star formation efficiency SFE = M⋆/M0. This fit agrees well with previous IMF results from the ramses, orion2, and sphng codes. Although M50 has no significant dependence on the magnetic field strength at the cloud scale, MHD is necessary to prevent a fragmentation cascade that results in non-convergent stellar masses. For initial conditions and SFE similar to star-forming GMCs in our Galaxy, we predict M50 to be $\gt 20 \, \mathrm{M}_{\odot }$, an order of magnitude larger than observed ($\sim 2 \, \mathrm{M}_\odot$), together with an excess of brown dwarfs. Moreover, M50 is sensitive to initial cloud properties and evolves strongly in time within a given cloud, predicting much larger IMF variations than are observationally allowed. We conclude that physics beyond MHD turbulence and gravity are necessary ingredients for the IMF.

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The Vertical Structure of the Galactic Disc

Symposium - International Astronomical Union ◽

10.1017/s0074180900109064 ◽

1995 ◽

Vol 164 ◽

pp. 389-389

Author(s):

M. Haywood ◽

A.C. Robin ◽

O. Bienaymé

Keyword(s):

Stellar Population ◽

Formation Rate ◽

Mass Range ◽

Mass Function ◽

Initial Mass Function ◽

Population Synthesis ◽

Intermediate Mass ◽

Star Count ◽

Stellar Population Synthesis ◽

Disc Formation

We have analyse star-count data in the direction of the Galactic Poles using a model of stellar population synthesis (Robin & Crézé (1986), Bienaymé, Robin & Crézé (1987)). The HR diagram for disc stars in the model is computed for a given star formation rate history and initial mass function (Haywood, 1994). In a paper submitted to A&A (Haywood et al.), we give a detailed investigation of the effects of these two functions on the simulated star-counts, and compare these with observed V, B-V data from V=5 to 22. We have obtained new constraints on the SFR, which we show has remained constant (to within a factor <3) since the disc formation, and on the IMF in the intermediate mass range (1-2 M⊙). Finally, we also obtain new constraint on the increase of vertical velocity dispersion with age. We state that if the disc does not containt any dynamically important dark mass, then this relation saturates at value smaller than 21 km.s−1.

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Do ultracompact dwarf galaxies form monolithically or as merged star cluster complexes?

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab330 ◽

2021 ◽

Vol 502 (4) ◽

pp. 5185-5199

Author(s):

Hamidreza Mahani ◽

Akram Hasani Zonoozi ◽

Hosein Haghi ◽

Tereza Jeřábková ◽

Pavel Kroupa ◽

...

Keyword(s):

Dwarf Galaxies ◽

Initial Conditions ◽

Mass Function ◽

Star Cluster ◽

Initial Mass Function ◽

Central Mass ◽

Cluster Complexes ◽

V Band ◽

Stellar Masses ◽

The Imf

ABSTRACT Some ultracompact dwarf galaxies (UCDs) have elevated observed dynamical V-band mass-to-light (M/LV) ratios with respect to what is expected from their stellar populations assuming a canonical initial mass function (IMF). Observations have also revealed the presence of a compact dark object in the centres of several UCDs, having a mass of a few to 15 per cent of the present-day stellar mass of the UCD. This central mass concentration has typically been interpreted as a supermassive black hole, but can in principle also be a subcluster of stellar remnants. We explore the following two formation scenarios of UCDs: (i) monolithic collapse and (ii) mergers of star clusters in cluster complexes as are observed in massively starbursting regions. We explore the physical properties of the UCDs at different evolutionary stages assuming different initial stellar masses of the UCDs and the IMF being either universal or changing systematically with metallicity and density according to the integrated Galactic IMF theory. While the observed elevated M/LV ratios of the UCDs cannot be reproduced if the IMF is invariant and universal, the empirically derived IMF that varies systematically with density and metallicity shows agreement with the observations. Incorporating the UCD-mass-dependent retention fraction of dark remnants improves this agreement. In addition, we apply the results of N-body simulations to young UCDs and show that the same initial conditions describing the observed M/LV ratios reproduce the observed relation between the half-mass radii and the present-day masses of the UCDs. The findings thus suggest that the majority of UCDs that have elevated M/LV ratios could have formed monolithically with significant remnant-mass components that are centrally concentrated, while those with small M/LV values may be merged star cluster complexes.

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Processes controlling the initial mass function: interstellar turbulence and magnetic fields

Symposium - International Astronomical Union ◽

10.1017/s0074180900239806 ◽

1991 ◽

Vol 147 ◽

pp. 407-408

Author(s):

R. C. Fleck

Keyword(s):

Magnetic Fields ◽

Mass Function ◽

Diffusion Time ◽

Interstellar Cloud ◽

Initial Mass Function ◽

Mass Scaling ◽

Interstellar Turbulence ◽

Time Scaling ◽

Turbulent Pressure ◽

Low Mass

The observed flattening of the initial stellar mass function at low mass can be accounted for in terms of the different interstellar cloud size-mass scaling and different ambipolar diffusion time scaling for small, thermally-supported clouds and larger clouds supported primarily by turbulent pressure.

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The IMF-SFH connection in massive early-type galaxies

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316007808 ◽

2015 ◽

Vol 11 (S315) ◽

Author(s):

I. Ferreras ◽

C. Weidner ◽

A. Vazdekis ◽

F. La Barbera

Keyword(s):

Age Distribution ◽

Stellar Populations ◽

Mass Function ◽

Initial Mass Function ◽

Population Synthesis ◽

Early Type ◽

Massive Galaxies ◽

Stellar Initial Mass Function ◽

The Many ◽

The Imf

The stellar initial mass function (IMF) is one of the fundamental pillars in studies of stellar populations. It is the mass distribution of stars at birth, and it is traditionally assumed to be universal, adopting generic functions constrained by resolved (i.e. nearby) stellar populations (e.g., Salpeter 1955; Kroupa 2001; Chabrier 2003). However, for the vast majority of cases, stars are not resolved in galaxies. Therefore, the interpretation of the photo-spectroscopic observables is complicated by the many degeneracies present between the properties of the unresolved stellar populations, including IMF, age distribution, and chemical composition. The overall good match of the photometric and spectroscopic observations of galaxies with population synthesis models, adopting standard IMF choices, made this issue a relatively unimportant one for a number of years. However, improved models and observations have opened the door to constraints on the IMF in unresolved stellar populations via gravity-sensitive spectral features. At present, there is significant evidence of a non-universal IMF in early-type galaxies (ETGs), with a trend towards a dwarf-enriched distribution in the most massive systems (see, e.g., van Dokkum & Conroy 2010; Ferreras et al. 2013; La Barbera et al. 2013). Dynamical and strong-lensing constraints of the stellar M/L in similar systems give similar results, with heavier M/L in the most massive ETGs (see, e.g., Cappellari et al. 2012; Posacki et al. 2015). Although the interpretation of the results is still open to discussion (e.g., Smith 2014; La Barbera 2015), one should consider the consequences of such a bottom-heavy IMF in massive galaxies.

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Metallicity effect and planet mass function in pebble-based planet formation models

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833347 ◽

2018 ◽

Vol 619 ◽

pp. A174 ◽

Cited By ~ 14

Author(s):

N. Brügger ◽

Y. Alibert ◽

S. Ataiee ◽

W. Benz

Keyword(s):

Internal Structure ◽

Planet Formation ◽

Large Fraction ◽

Mass Function ◽

Planetary Atmosphere ◽

Population Synthesis ◽

Core Accretion ◽

Mass Functions ◽

Synthesis Approach ◽

Gaseous Envelope

Context. One of the main scenarios of planet formation is the core accretion model where a massive core forms first and then accretes a gaseous envelope. This core forms by accreting solids, either planetesimals or pebbles. A key constraint in this model is that the accretion of gas must proceed before the dissipation of the gas disc. Classical planetesimal accretion scenarios predict that the time needed to form a giant planet’s core is much longer than the time needed to dissipate the disc. This difficulty led to the development of another accretion scenario, in which cores grow by accretion of pebbles, which are much smaller and thus more easily accreted, leading to more rapid formation. Aims. The aim of this paper is to compare our updated pebble-based planet formation model with observations, in particular the well-studied metallicity effect. Methods. We adopt the Bitsch et al. (2015a, A&A, 575, A28) disc model and the Bitsch et al. (2015b, A&A, 582, A112) pebble model and use a population synthesis approach to compare the formed planets with observations. Results. We find that keeping the same parameters as in Bitsch et al. (2015b, A&A, 582, A112) leads to no planet growth due to a computation mistake in the pebble flux (2018b). Indeed a large fraction of the heavy elements should be put into pebbles (Zpeb∕Ztot = 0.9) in order to form massive planets using this approach. The resulting mass functions show a huge amount of giants and a lack of Neptune-mass planets, which are abundant according to observations. To overcome this issue we include the computation of the internal structure for the planetary atmosphere in our model. This leads to the formation of Neptune-mass planets but no observable giants. Furthermore, reducing the opacity of the planetary envelope more closely matches observations. Conclusions. We conclude that modelling the internal structure for the planetary atmosphere is necessary to reproduce observations.

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Supernova Nucleosynthesis in Massive Stars

International Astronomical Union Colloquium ◽

10.1017/s0252921100008022 ◽

1996 ◽

Vol 145 ◽

pp. 157-164

Author(s):

M. Hashimoto ◽

K. Nomoto ◽

T. Tsujimoto ◽

F.-K. Thielemann

Keyword(s):

Main Sequence ◽

Massive Stars ◽

Mass Function ◽

Stellar Mass ◽

Initial Mass Function ◽

Explosion Energy ◽

Initial Mass ◽

Explosive Nucleosynthesis ◽

Solar Abundances

Presupernova evolution and explosive nucleosynthesis in massive stars for main-sequence masses from 13 Mʘ to 70 Mʘ are calculated. We examine the dependence of the supernova yields on the stellar mass, 12C(α, γ)16O rate, and explosion energy. The supernova yields integrated over the initial mass function are compared with the solar abundances.

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