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Population III star formation in an X-ray background – II. Protostellar discs, multiplicity, and mass function of the stars
- Source :
- Monthly Notices of the Royal Astronomical Society. 508:6193-6208
- Publication Year :
- 2021
- Publisher :
- Oxford University Press (OUP), 2021.
-
Abstract
- 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 far-ultraviolet H2-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 2 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 top-heavy 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 likely 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.
- Subjects :
- Physics
education.field_of_study
Cosmology and Nongalactic Astrophysics (astro-ph.CO)
Initial mass function
Star formation
Population
X-ray background
FOS: Physical sciences
Astronomy and Astrophysics
Astrophysics
Astrophysics - Astrophysics of Galaxies
Accretion (astrophysics)
Momentum
Stars
Space and Planetary Science
Astrophysics of Galaxies (astro-ph.GA)
Protostar
education
Astrophysics - Cosmology and Nongalactic Astrophysics
Subjects
Details
- ISSN :
- 13652966 and 00358711
- Volume :
- 508
- Database :
- OpenAIRE
- Journal :
- Monthly Notices of the Royal Astronomical Society
- Accession number :
- edsair.doi.dedup.....8f3fd66b3e7102342d65875313a4ecc1