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Can the 21-cm signal probe Population III and II star formation?

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Original languageEnglish
Pages (from-to)654-665
Number of pages12
JournalMonthly Notices of the Royal Astronomical Society
Volume448
Issue number1
DOIs
StatePublished - 21 Mar 2015

Abstract

Using varying models for the star formation rate (SFR) of Population (Pop) III and II stars at z > 6 we derive the expected redshift history of the global 21-cm signal from the intergalactic medium (IGM). To recover the observed Thomson scattering optical depth of the cosmic microwave background (CMB) requires SFRs at the level of similar to 10-3M(circle dot) yr(-1) Mpc(-3) at z similar to 15 from Pop III stars, or similar to 10(-1)M(circle dot) yr(-1) Mpc-3 at z similar to 7 from Pop II stars. In the case the SFR is dominated by Pop III stars, the IGM quickly heats above the CMB at z similar to 12 due to heating from supernovae. In addition, Ly alpha photons from haloes hosting Pop III stars couple the spin temperature to that of the gas, resulting in a deep absorption signal. If the SFR is dominated by Pop II stars, the IGM slowly heats and exceeds the CMB temperature at z similar to 10. However, the larger and varying fraction of Pop III stars are able to break this degeneracy. We find that the impact of the initial mass function (IMF) of Pop III stars on the 21-cm signal results in an earlier change to a positive signal if the IMF slope is similar to-1.2. Measuring the 21-cm signal at z greater than or similar to 10 with next generation radio telescopes such as the Square Kilometre Array will be able to investigate the contribution from Pop III and Pop II stars to the global SFR.

    Research areas

  • stars: Population II, galaxies: formation, galaxies: high-redshift, dark ages, reionization, first stars, diffuse radiation, SUPERMASSIVE BLACK-HOLES, LY-ALPHA EMITTERS, SIMILAR-TO 7, UV LUMINOSITY FUNCTIONS, ACTIVE GALACTIC NUCLEI, INITIAL MASS FUNCTION, BILLION YEARS PROJECT, LYMAN-BREAK GALAXIES, GAMMA-RAY BURSTS, 21 CM SIGNAL

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