The SPHINX Cosmological Simulations of the First Billion Years: the Impact of Binary Stars on Reionization★

By J. Rosdahl, H. Katz, Jérémy Blaizot, T. Kimm, L. Michel-Dansac, T. Garel, M. Haehnelt, P. Ocvirk, Romain Teyssier. Monthly notices of the Royal Astronomical Society, 2018

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We present the SPHINX suite of cosmological adaptive mesh refinement simulations, the first radiation-hydrodynamical simulations to simultaneously capture large-scale reionization and the escape of ionizing radiation from thousands of resolved galaxies. Our $5$ and $10$ co-moving Mpc volumes resolve haloes down to the atomic cooling limit and model the inter-stellar medium with better than $\approx10$ pc resolution. The project has numerous goals in improving our understanding of reionization and making predictions for future observations. In this first paper we study how the inclusion of binary stars in computing stellar luminosities impacts reionization, compared to a model that includes only single stars. Owing to the suppression of galaxy growth via strong feedback, our galaxies are in good agreement with observational estimates of the galaxy luminosity function. We find that binaries have a significant impact on the timing of reionization: with binaries, our boxes are $99.9$ percent ionized by volume at $z\approx 7$, while without them our volumes fail to reionize by $z=6$. These results are robust to changes in volume size, resolution, and feedback efficiency. The escape of ionizing radiation from individual galaxies varies strongly and frequently. On average, binaries lead to escape fractions of $\approx 7-10$ percent, about $3.5$ times higher than with single stars only. The higher escape fraction is a result of a shallower decline in ionizing luminosity with age, and is the primary reason for earlier reionization, although the higher integrated luminosity with binaries also plays a sub-dominant role.

Subfields: Astronomy and Astrophysics, Instrumentation

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Citations in the corpus

A Redshift-independent Efficiency Model: Star Formation and Stellar Masses in Dark Matter Halos at z ≳ 4 (2018, background): “…of momentum coming from the (unresolved) expansion of gaseous shells from supernovae and stellar winds (Ostriker & Shetty 2011); (ii) SPHINX (Rosdahl et al. 2018), a suite of simulations that includes a series of cosmological boxes with volume (5-10 cMpc)3, in which halos are well resolved…”
Rapid Reionization by the Oligarchs: The Case for Massive, UV-bright, Star-forming Galaxies with High Escape Fractions (2019, background): “…turbulence, and feedback carving out channels in the ISM through which LyC photons can stream out of the galaxy (e.g., Ma et al. 2016; Safarzadeh & Scannapieco 2016; Sharma et al. 2016; Trebitsch et al. 2017; Katz et al. 2018; Rosdahl et al. 2018; Kakiichi & Gronke 2019; Kimm et al. 2019).”
Conditions for Reionizing the Universe with a Low Galaxy Ionizing Photon Escape Fraction (2019, background): “Our model’s luminosity functions thus extend a redshift-dependent 1–2 mag fainter than other studies (e.g., Finkelstein et al. 2012a; Bouwens et al. 2015a; R15), though they are consistent with values seen in recent simulations (e.g., Gnedin 2016; Rosdahl et al. 2018; Yung et al. 2019).”
On the stunning abundance of super-early, luminous galaxies revealed by JWST (2022, background): “A number of theoretical approaches, ranging from numerical simulations (e.g. Vogelsberger et al. 2014; Schaye et al. 2015; Rosdahl et al. 2018; Pillepich et al. 2018; Hopkins et al. 2018; Davé et al. 2019; Trebitsch et al. 2021; Pallottini et al. 2022) to semi-analytic models (e.g. Dayal et al.…”
Large Ly α opacity fluctuations and low CMB τ in models of late reionization with large islands of neutral hydrogen extending to z < 5.5 (2018, background): “…to the evolution of the escape fraction of ionizing photons from galaxies, possibly due to changes in morphology, stellar populations, and dust con- tent of these galaxies (Rosdahl et al. 2018; Trebitsch et al. 2017; Kimm et al. 2017; Paardekooper et al. 2015; Kimm & Cen 2014; Yajima et al. 2011).”