Stellar population effects on the inferred photon density at reionization

By E. Stanway, J. Eldridge, George D. Becker. 2015

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The relationship between stellar populations and the ionizing flux with which they irradiate their surroundings has profound implications for the evolution of the intergalactic medium (IGM). We quantify the ionizing flux arising from synthetic stellar populations which incorporate the evolution of interacting binary stars. We determine that these show ionizing flux boosted by 60 per cent at 0.05 ≤ Z ≤ 0.3 Z⊙ and a more modest 10–20 per cent at near-solar metallicities relative to star-forming populations in which stars evolve in isolation. The relation of ionizing flux to observables such as 1500 A continuum and ultraviolet spectral slope is sensitive to attributes of the stellar population including age, star formation history and initial mass function (IMF). For a galaxy forming 1 M⊙ yr−1, observed at >100 Myr after the onset of star formation, we predict a production rate of photons capable of ionizing hydrogen, Nion = 1.4 × 1053 s−1 at Z = Z⊙ and 3.5 × 1053 s−1 at 0.1 Z⊙, assuming a Salpeter-like IMF. We evaluate the impact of these issues on the ionization of the IGM, finding that the known galaxy populations can maintain the ionization state of the Universe back to z ∼ 9, assuming that their luminosity functions continue to MUV = −10, and that constraints on the IGM at z ∼ 2–5 can be satisfied with modest Lyman-continuum photon escape fractions of 4–24 per cent depending on assumed metallicity.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/a1d4f1b63ffc075fa4c77251361c6210d9b9d21b

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Citations in the corpus

• Lyα and C iii] emission in z = 7–9 Galaxies: accelerated reionization around luminous star-forming systems? (2016, background): “…the ionizing output of star forming systems may be sufficient to complete reionization by z ' 6 while also supplying the IGM with enough free electrons at z ' 9 to reproduce the measured Thomson scattering optical depth of the CMB (Robertson et al. 2015; Bouwens et al. 2015a; Stanway et al. 2016).”
• The SPHINX Cosmological Simulations of the First Billion Years: the Impact of Binary Stars on Reionization★ (2018, methodology): “Ionizing luminosities (LM ; upper panel) and cumulative number of hydrogen-ionizing photons ( ; lower panel) as a function of stellar population age for SED models with single stars only (Bruzual & Charlot 2003) in red and binary stars (Stanway et al. 2016) in blue.”
• Nebular Continuum and Line Emission in Stellar Population Synthesis Models (2016, methodology): “The Padova+Geneva isochrones used in this work do not include the effects of stellar rotation or binarity, both of which have important effects on the ionizing spectrum and main sequence lifetimes of massive stars (e.g., Eldridge & Stanway 2012; Levesque et al. 2012; Stanway et al. 2016).”
• Nebular Emission Line Ratios in z ≃ 2–3 Star-forming Galaxies with KBSS-MOSFIRE: Exploring the Impact of Ionization, Excitation, and Nitrogen-to-Oxygen Ratio (2016, methodology): “Here, we employ stellar population models from the most recent version of “Binary Population and Spectral Synthesis” (BPASSv2; Stanway et al. 2016, Eldridge et al. in prep.).”
• Binary Population and Spectral Synthesis Version 2.1: Construction, Observational Verification, and New Results (2017, methodology): “…number of papers have already been published exploring this area, notably Steidel et al. (2016) on applications to galaxies at Cosmic Noon (z ∼ 2 − 3), Stanway et al. (2016) and Ma et al. (2016) on implications for reionisation and Wilkins et al. (2016) for application to semi-analytic galaxy…”
• The HDUV Survey: A Revised Assessment of the Relationship between UV Slope and Dust Attenuation for High-redshift Galaxies (2017, methodology): “…the relationship between IRX and β using the recently developed “Binary Population and Spectral Synthesis” (BPASS) models (Eldridge & Stanway 2012; Stanway et al. 2016) with a stellar metallicity of Z = 0.14Z on the current abundance scale (Asplund et al. 2009) and a two power-law IMF with α…”
• RECONCILING THE STELLAR AND NEBULAR SPECTRA OF HIGH-REDSHIFT GALAXIES (2016, methodology): “We have also included a suite of models from the new release of “Binary Population and Spectral Synthesis” (BPASSv214; Eldridge & Stanway 2016; Stanway et al. 2016) all with an IMF index of −2.35.”
• Fluctuating feedback-regulated escape fraction of ionizing radiation in low-mass, high-redshift galaxies (2017, background): “Stanway et al. (2016) proposed that binary interactions might result in a similar enhancement of the ionizing luminosity.”
• Feedback-regulated star formation and escape of LyC photons from mini-haloes during reionization (2016, methodology): “The interactions of binary stars can not only increase the total number of LyC photons, but also make the decline of the production rate slower, as the primary star transfers gas to the secondary, removes the hydrogen envelope, and the stars merge (Stanway et al. 2016).”
• Re-evaluating old stellar populations (2018, background): “We modify the grid described in ES17, adding single star models such that the grid samples: (i) every 0.02 M in the range 0.1-2.0 M , (ii) every 0.05 M in the range 2.0-3.0 M , (iii) every 0.1 M in the range 3.0-10 M , (iv) every 1 M in the range 10-100 M , and (v) every 25 M in the range 100-300 M ”
• ALMA SPECTROSCOPIC SURVEY IN THE HUBBLE ULTRA DEEP FIELD: THE INFRARED EXCESS OF UV-SELECTED z = 2–10 GALAXIES AS A FUNCTION OF UV-CONTINUUM SLOPE AND STELLAR MASS (2016, background): “…the bluest UV continuum slopes β (β < −2.3) and very close to the values suggested by the stellar population models including the impact of binary stars on the evolution (e.g., Stanway et al. 2016; Wilkins et al. 2016b) or suggested by models including stellar rotation (e.g., Topping & Shull 2015).”