Generic Spectrum and Ionization Efficiency of a Heavy Initial Mass Function for the First Stars

By Volker Bromm, R. Kudritzki, Abraham Loeb. 2000

347 citations recorded by the source corpus.

We calculate the generic spectral signature of an early population of massive stars at high redshifts. For metal-free stars with mass above 300 M☉, we find that the combined spectral luminosity per unit stellar mass is almost independent of the mass distribution of these stars. To zeroth order, the generic spectrum resembles a blackbody with an effective temperature of ~105 K, making these stars highly efficient at ionizing hydrogen and helium. The production rate of ionizing radiation per stellar mass by stars more massive than ~300 M☉ is larger by ~1 order of magnitude for hydrogen and He I and by ~2 orders of magnitude for He II than the emission from a standard initial mass function. This would result in unusually strong hydrogen and helium recombination lines from the surrounding interstellar medium. It could also alleviate the current difficulty of ionizing the intergalactic medium at z ≳ 6 with the cosmic star formation rate inferred at somewhat lower redshifts.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/ad943f78520db6f3bfb99b84f24d1b5a19de4bd2

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Citations in the corpus

• Wouthuysen-Field coupling strength and application to high-redshift 21-cm radiation (2005, background): “Their ǫb(ν) is assumed to be a blackbody of temperature 105 K, as appropriate for massive Population III stars withM > 300M⊙ (Bromm et al. 2001); the blackbody is normalized to a total energy of 7.1 MeV per H nucleus or 5.4 MeV per baryon, appropriate for complete hydrogen burning to 4He.”
• Two populations of metal-free stars in the early Universe (2006, background): “…to remaining uncertainties we choose the more robust value Zcrit = 10 −3.5 Z⊙, which is based on the physics of fine structure cooling, and does not depend on whether dust is present or not, and if so, what its composition might be (e.g. Bromm et al. 2001a; Bromm & Loeb 2003; Santoro & Shull 2006).”
• 21 cm cosmology in the 21st century (2011, background): “stars to form from the collapse of primordial gas are very massive (∼10–100 M ) Population III stars [44].”
• Reionization of Hydrogen and Helium by Early Stars and Quasars (2002, background): “In addition to the above constraints, observations suggest that the IGM was metal enriched by z 6 (Songaila 2001) to a level that would lead to a Scalo stellar mass function (Bromm et al. 2001) if new galaxies formed out of it.”
• The Complete CEERS Early Universe Galaxy Sample: A Surprisingly Slow Evolution of the Space Density of Bright Galaxies at z ∼ 8.5–14.5 (2023, background): “…rest-UV spectroscopic observations could be capable of detecting high-ionization lines such as He II or [ Ne V ] , which could indicate the presence of very massive stars in these galaxies ( e.g., Tumlinson & Shull 2000; Bromm et al. 2001; Schaerer 2003; Olivier et al. 2022; Cleri et al. 2023 ) .”
• Predicted UV properties of very metal-poor starburst galaxies (2010, background): “These and other studies (see e.g. Tumlinson & Shull 2000; Tumlinson et al. 2001; Bromm et al. 2001) have in particular Send offprint requests to: A. Raiter highlighted the use of strong Lyα emission and nebular Heii emission to search for objects containing Population III (hereafter Pop III) stars.”
• Self-regulated reionization (2006, background): “Massive stars are more efficient producers of ionizing photons, emitting up toNi ∼ 105 ionizing photons per stellar atom (Bromm et al. 2001; Schaerer 2002; Venkatesan & Truran 2003).”
• Bright OB stars in the Galaxy. III. Constraints on the radial stratification of the clumping factor (2006, background): “…last few years, massive stars (MZAMS >∼ 10 M ) have (re-)gained considerable interest among the astrophysical community, in particular because of their role in the development of the early Universe (e.g., its chemical evolution and reionization; Bromm et al. 2001, but also Matteucci & Calura 2005).”
• On the properties of massive Population III stars and metal-free stellar populations (2001, background): “The comparison of the total spectrum (solid line) with the pure stellar emission (dashed) illustrates the importance of nebular continuous emission neglected in earlier studies (TS00, Bromm et al. 2001), which dominates the ZAMS spectrum at λ >∼ 1400 Å.”
• Fossil H ii regions: self-limiting star formation at high redshift (2003, background): “We argue that this is unlikely, for two reasons: 1) Metal line cooling only dominates H2 cooling above a critical metallicity Z > 10−3Z⊙ (Bromm et al 2001; Hellsten & Lin 1997).”
• Cosmological Parameter Estimation Using 21 cm Radiation from the Epoch of Reionization (2005, background): “Values of P 10Y40 are reasonable for normal star formation, but very massive stars can increase the efficiency by an order of magnitude (Bromm et al. 2001).”
• Stellar and wind parameters of Galactic O-stars - The influence of line-blocking/blanketing (2004, background): “In the distant Universe, massive stars dominate the integrated UV-light of very young galaxies (Steidel et al. 1996; Pettini et al. 2000); even earlier they are the suspected sources of the re-ionization of the Universe (Bromm et al. 2001).”
• CEERS Key Paper. I. An Early Look into the First 500 Myr of Galaxy Formation with JWST (2022, background): “One such diagnostic is the predicted boost to nebular line emission, including the occurrence of strong He II 1640 Å features (e.g., Bromm et al. 2001; Raiter et al. 2010), accessible via our upcoming CEERS spectroscopic follow-up.”