A hint on the metal-free star formation rate density from 21-cm-EDGES data. Issue 2 (8th June 2020)

• Record Type: Journal Article
• Authors: Chatterjee, Atrideb; Dayal, Pratika; Choudhury, Tirthankar Roy; Schneider, Raffaella
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 496:Issue 2(2020)
• Page Start: 1445
• Page End: 1452
• Publication Date: 2020-06-08
• Subjects: stars: Population II -- stars: Population III -- galaxies: high-redshift -- intergalactic medium -- dark ages, reionization, first stars; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/staa1609
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: We aim to provide here the first data-constrained estimate of the metal-free (Population III; Pop III) star formation rate density $\dot{\rho }_{*}^{III}$ required at high redshifts ($z \lower.5ex\hbox{$\, \, \buildrel\gt \over \sim \, \, $}16$ ) in order to reproduce both the amplitude and the redshift of the EDGES 21-cm global signal. Our model accounts for the Ly α, radio, and X-ray backgrounds from both Pop III and metal-enriched Population II (Pop II) stars. For the latter, we use the star formation rate density estimates (and the Ly α background) from the Delphi semi-analytic model that has been shown to reproduce all key observables for galaxies at $z \lower.5ex\hbox{$\, \, \buildrel\gt \over \sim \, \, $}5$ ; the radio and X-ray backgrounds are fixed using low- z values. The constraints on the free parameters characterizing the properties of the Pop III stars are obtained using a Markov Chain Monte Carlo analysis. Our results yield a $\dot{\rho }_{*}^{III}$ that while increasing from z ∼ 21 to 16 thereafter shows a sharp decline which is in excellent agreement with the results found by Valiante et al. to simulate the growth of z ∼ 6–7 quasars and their host galaxies, suggesting that the bulk of Pop III star formation occurs in the rarest and most massive metal-poor haloes at z ≲ 20. This allows Pop III stars to produce a rapidly growing Ly α background between z ∼ 21 and 15. Further, Pop III stars are required to provide a radio background that is about 3–4 orders of magnitude higher than that provided by Pop II stars although Pop II stars dominate the X-ray background.