Forming Pop III binaries in self-gravitating discs: how to keep the orbital angular momentum

Chon, Sunmyon; Hosokawa, Takashi

doi:10.1093/mnras/stz1824

Cited by 38 publications

(23 citation statements)

References 109 publications

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“…The two clumps equally grow, and their mass ratio approaches to unity (Fig. 11, see also Chon & Hosokawa 2019). The more vigorous fragmentation starts slightly after 𝛥𝑡 = 10 3 yr with 𝛽 = 0.09 (Fig.…”

Section: Mass Distribution Of Self-gravitating Clumpsmentioning

confidence: 89%

Gravitational Fragmentation of Extremely Metal-poor Circumstellar Discs

Shima,

Hosokawa

2021

Preprint

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We study the gravitational fragmentation of circumstellar discs accreting extremely metal-poor (𝑍 ≤ 10 −3 Z ) gas, performing a suite of three-dimensional hydrodynamic simulations using the adaptive mesh refinement code Enzo. We systematically follow the long-term evolution for 2 × 10 3 years after the first protostar's birth, for the cases of 𝑍 = 0, 10 −5 , 10 −4 , and 10 −3 Z . We show that evolution of number of self-gravitating clumps qualitatively changes with 𝑍. Vigorous fragmentation induced by dust cooling occurs in the metal-poor cases, temporarily providing ∼ 10 self-gravitating clumps at 𝑍 = 10 −5 and 10 −4 Z . However, we also show that the fragmentation is a very sporadic process; after an early episode of the fragmentation, the number of clumps continuously decreases as they merge away in these cases. The vigorous fragmentation tends to occur later with the higher 𝑍, reflecting that the dust-induced fragmentation is most efficient at the lower density. At 𝑍 = 10 −3 Z , as a result, the clump number stays smallest until the disc fragmentation starts in a late stage. We also show that the clump mass distribution also depends on the metallicity. A single or binary clump substantially more massive than the others appear only at 𝑍 = 10 −3 Z , whereas they are more evenly distributed in mass at the lower metallicities. We suggest that the disc fragmentation should provide the stellar multiple systems, but their properties drastically change with a tiny amount of metals.

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Section: Mass Distribution Of Self-gravitating Clumpsmentioning

confidence: 89%

Gravitational Fragmentation of Extremely Metal-poor Circumstellar Discs

Shima,

Hosokawa

2021

Preprint

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“…The fragment grows in mass via accreting the surrounding gas and grows into massive protostars. As a result, hierarchical binary systems form as seen in simulations of star formation in primordial environments (Chon et al 2018;Chon & Hosokawa 2019;Susa 2019;Sugimura et al 2020). The effect of dust thermal emission is only seen very close to the massive protostars within 100 au, which produces small fragments as shown in the Z/Z = 10 −4 case since dust cooling becomes efficient only when n 10 11 cm −3 .…”

Section: Formation and Evolution Of The Protostellar Systemmentioning

confidence: 95%

“…Dust cooling induces vigorous fragmentation inside the disk and produces a number of low-mass stars, while they are easily ejected from the system as they experience many-body interactions with other stars (Clark et al 2008;Dopcke et al 2013;Safranek-Shrader et al 2016;Chon & Omukai 2020) or migrate inward due to the interaction with the disk gas and merge with the central stars (e.g. Tanaka et al 2002;Chon & Hosokawa 2019). This makes the massive stars more massive, producing a high-mass stellar component distinctive from the distribution of the low-mass stellar component.…”

Section: Transition From Top-heavy To Present-day Imfmentioning

confidence: 99%

Transition of the initial mass function in the metal-poor environments

Chon,

Omukai,

Schneider

2021

Preprint

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We study star cluster formation in a low-metallicity environment using three dimensional hydrodynamic simulations. Starting from a turbulent cloud core, we follow the formation and growth of protostellar systems with different metallicities ranging from 10 −6 to 0.1 Z . The cooling induced by dust grains promotes fragmentation at small scales and the formation of low-mass stars with M * ∼ 0.01-0.1 M when Z/Z 10 −5 . While the number of low-mass stars increases with metallicity, the stellar mass distribution is still top-heavy for Z/Z 10 −2 compared to the Chabrier initial mass function (IMF). In these cases, star formation begins after the turbulent motion decays and a single massive cloud core monolithically collapses to form a central massive stellar system. The circumstellar disk preferentially feeds the mass to the central massive stars, making the mass distribution top-heavy. When Z/Z = 0.1, collisions of the turbulent flows promote the onset of the star formation and a highly filamentary structure develops owing to efficient fine-structure line cooling. In this case, the mass supply to the massive stars is limited by the local gas reservoir and the mass is shared among the stars, leading to a Chabrier-like IMF. We conclude that cooling at the scales of the turbulent motion promotes the development of the filamentary structure and works as an important factor leading to the present-day IMF.

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“…One important aspect of the formation of Pop III star is the survival of the stars after disc fragmentation. Previous simulations showed that while the inward migration of secondary stars leads to the merger with the primary stars, protostars are also observed to migrate outward (see Greif et al 2012;Stacy & Bromm 2013;Stacy et al 2016;Hirano & Bromm 2017;Susa 2019;Chon & Hosokawa 2019;Sugimura et al 2020). The star migration is affected by gas in the disc through two main processes: i) accretion of gas with higher angular momentum of the protostar produces an outward migration (in a Keplerian disc it's the gas with orbit outward of the protostar orbit); ii) dynamical friction and gravitational torques mediated by resonances, produce a migration inward of the protostars by loss of their angular momentum and energy to the disc.…”

Section: Results: II Multiplicity and Migration Of Population Iii Starsmentioning

confidence: 99%

Population III Star Formation in an X-ray background: II. Protostellar Discs, Multiplicity and Mass Function of the Stars

Park,

Ricotti,

Sugimura

2021

Preprint

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Disc fragmentation plays an important role in determining the number of primordial stars (Pop III stars), their masses, and hence the initial mass function. In this second paper of a series, we explore the effect of uniform FUV H 2 -photodissociating and X-ray radiation backgrounds on the formation of Pop III stars using a grid of high-resolution zoom-in simulations. We find that, in an X-ray background, protostellar discs have lower surface density and higher Toomre 𝑄 parameter, so they are more stable. For this reason, X-ray irradiated discs undergo fewer fragmentations and typically produce either binary systems or low-multiplicity systems. In contrast, the cases with weak or no X-ray irradiation produce systems with a typical multiplicity of 6 ± 3. In addition, the most massive protostar in each system is smaller by roughly a factor of two when the disc is irradiated by X-rays, due to lower accretion rate. With these two effects combined, the initial mass function of fragments becomes more topheavy in a strong X-ray background and is well described by a power-law with slope 1.53 and high-mass cutoff of 61 M . Without X-rays, we find a slope 0.49 and cutoff mass of 229 M . Finally, protostars migrate outward after their formation due to the accretion of high-angular momentum gas from outside and the migration is more frequent and significant in absence of X-ray irradiation.

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Forming Pop III binaries in self-gravitating discs: how to keep the orbital angular momentum

Cited by 38 publications

References 109 publications

Gravitational Fragmentation of Extremely Metal-poor Circumstellar Discs

Gravitational Fragmentation of Extremely Metal-poor Circumstellar Discs

Transition of the initial mass function in the metal-poor environments

Population III Star Formation in an X-ray background: II. Protostellar Discs, Multiplicity and Mass Function of the Stars

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