Three modes of metal-enriched star formation at high redshift

Britton D. Smith, Matthew J. Turk, Steinn Sigurdsson, Brian W. O'Shea, Michael L. Norman

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

It is generally accepted that the very first stars in the universe were significantly more massive and formed much more in isolation than stars observed today. This suggests that there was a transition in star formation modes that was most likely related to the metallicity of the star-forming environment. We study how the addition of heavy elements alters the dynamics of collapsing gas by performing a series of numerical simulations of primordial star formation with various levels of pre-enrichment, using the adaptive mesh refinement, hydrodynamic + N-body code, Enzo. At high redshifts, the process of star formation is heavily influenced by the cosmic microwave background (CMB), which creates a temperature floor for the gas. Our results show that cloud-collapse can follow three distinct paths, depending on the metallicity. For very low metallicities (log10(Z/Z) < -3.5), star formation proceeds in the primordial mode, producing only massive, singular objects. For high metallicities (log10(Z/Z) > -3), efficient cooling from the metals cools the gas to the CMB temperature when the core density is still very low. When the gas temperature reaches the CMB temperature, the core becomes very thermally stable, and further fragmentation is heavily suppressed. In our simulations with log10(Z/Z) > -3, only a single object forms with a mass-scale of a few hundred M. We refer to this as the CMB-regulated star formation mode. For metallicities between these two limits (-3.5 < log10(Z/Z) < -3), the gas cools efficiently, but never reaches the CMB temperature. In this mode, termed the metallicity-regulated star formation mode, the minimum gas temperature is reached at much higher densities, allowing the core to fragment and form multiple objects with mass-scales of only a few M. Our results imply that the stellar initial mass function was top-heavy at very high redshift due to stars forming in the CMB-regulated mode. As the CMB temperature lowers with time, the metallicity-regulated star formation mode (producing multiple low-mass stars) operates at higher metallicities and eventually becomes the sole mode of star formation.

Original languageEnglish (US)
Title of host publicationLow-Metallicity Star Formation
Subtitle of host publicationFrom the First Stars to Dwarf Galaxies
Pages111-115
Number of pages5
EditionS255
DOIs
StatePublished - Dec 22 2008

Publication series

NameProceedings of the International Astronomical Union
NumberS255
Volume4
ISSN (Print)1743-9213
ISSN (Electronic)1743-9221

Fingerprint

metallicity
star formation
microwaves
metals
stars
gas temperature
gases
Population III stars
temperature
heavy elements
isolation
fragmentation
simulation
universe
hydrodynamics
fragments
cooling

All Science Journal Classification (ASJC) codes

  • Medicine (miscellaneous)
  • Astronomy and Astrophysics
  • Nutrition and Dietetics
  • Public Health, Environmental and Occupational Health
  • Space and Planetary Science

Cite this

Smith, B. D., Turk, M. J., Sigurdsson, S., O'Shea, B. W., & Norman, M. L. (2008). Three modes of metal-enriched star formation at high redshift. In Low-Metallicity Star Formation: From the First Stars to Dwarf Galaxies (S255 ed., pp. 111-115). (Proceedings of the International Astronomical Union; Vol. 4, No. S255). https://doi.org/10.1017/S1743921308024666
Smith, Britton D. ; Turk, Matthew J. ; Sigurdsson, Steinn ; O'Shea, Brian W. ; Norman, Michael L. / Three modes of metal-enriched star formation at high redshift. Low-Metallicity Star Formation: From the First Stars to Dwarf Galaxies. S255. ed. 2008. pp. 111-115 (Proceedings of the International Astronomical Union; S255).
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Smith, BD, Turk, MJ, Sigurdsson, S, O'Shea, BW & Norman, ML 2008, Three modes of metal-enriched star formation at high redshift. in Low-Metallicity Star Formation: From the First Stars to Dwarf Galaxies. S255 edn, Proceedings of the International Astronomical Union, no. S255, vol. 4, pp. 111-115. https://doi.org/10.1017/S1743921308024666

Three modes of metal-enriched star formation at high redshift. / Smith, Britton D.; Turk, Matthew J.; Sigurdsson, Steinn; O'Shea, Brian W.; Norman, Michael L.

Low-Metallicity Star Formation: From the First Stars to Dwarf Galaxies. S255. ed. 2008. p. 111-115 (Proceedings of the International Astronomical Union; Vol. 4, No. S255).

Research output: Chapter in Book/Report/Conference proceedingConference contribution

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Smith BD, Turk MJ, Sigurdsson S, O'Shea BW, Norman ML. Three modes of metal-enriched star formation at high redshift. In Low-Metallicity Star Formation: From the First Stars to Dwarf Galaxies. S255 ed. 2008. p. 111-115. (Proceedings of the International Astronomical Union; S255). https://doi.org/10.1017/S1743921308024666