A NEW CALCULATION OF THE IONIZING BACKGROUND SPECTRUM AND THE EFFECTS OF He ii REIONIZATION

By C. Faucher-Giguére, A. Lidz, M. Zaldarriaga, Lars Hernquist. 2009

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The ionizing background determines the ionization balance and the thermodynamics of the cosmic gas. It is therefore a fundamental ingredient to theoretical and empirical studies of both the intergalactic medium (IGM) and galaxy formation. We present here a new calculation of its spectrum that satisfies the empirical constraints we recently obtained by combining state-of-the-art luminosity functions and intergalactic opacity measurements. In our preferred model, star-forming galaxies and quasars each contribute substantially to the H i ionizing field at z < 3, with galaxies rapidly overtaking quasars at higher redshifts as quasars become rarer. In addition to our fiducial model, we explore the physical dependences of the calculated background and clarify how recombination emission contributes to the ionization rates. We find that recombinations do not simply boost the ionization rates by the number of re-emitted ionizing photons as many of these rapidly redshift below the ionization edges and have a distribution of energies. A simple analytic model that captures the main effects seen in our numerical radiative transfer calculations is given. Finally, we discuss the effects of He ii reionization by quasars on both the spectrum of the ionizing background and on the thermal history of the IGM. In regions that have yet to be reionized, the spectrum is expected to be almost completely suppressed immediately above 54.4 eV, while a background of higher energy (≳0.5 keV) photons permeates the entire universe owing to the frequency dependence of the photoionization cross section. We provide an analytical model of the heat input during He ii reionization and its effects on the temperature–density relation.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/84adc2cecf391f756d090b68b944f35213568fbb

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Citations in the corpus

The z ∼ 6 Luminosity Function Fainter than −15 mag from the Hubble Frontier Fields: The Impact of Magnification Uncertainties (2016, methodology): “Radiation cooling is included in the simulations by H, He, and metals (Choi & Nagamine 2009), a UV background self-shielding effect, and heating by a uniform UV background (Faucher-Giguère et al. 2009).”
The Auriga Project: the properties and formation mechanisms of disc galaxies across cosmic time (2016, methodology): “Following the model of Faucher-Giguère et al. (2009), a spatially uniform UV background field is included, which completes reionization at redshift z ∼ 6 (for more details, see Vogelsberger et al. 2013).”
Gravitational torque-driven black hole growth and feedback in cosmological simulations (2016, methodology): “We include radiative cooling from primordial gas (Katz, Weinberg & Hernquist 1996), metal-line cooling (Wiersma, Schaye & Smith 2009), and photoionization heating from an optically thin UV background (Faucher-Giguère et al. 2009).”
New Measurements of the Ionizing Ultraviolet Background over 2 < z < 5 and Implications for Hydrogen Reionization (2013, background): “This is similar to, though slightly lower than, the amplitude found by Faucher-Giguère et al. (2009) for their fiducial set of parameters.”
RADIATIVE TRANSFER IN A CLUMPY UNIVERSE. IV. NEW SYNTHESIS MODELS OF THE COSMIC UV/X-RAY BACKGROUND (2011, methodology): “It is in this second step that our approach differs from that of Faucher-Giguère et al. (2009).”
The impact of baryonic physics on the structure of dark matter haloes: the view from the FIRE cosmological simulations (2015, methodology): “We use global ultraviolet background model from Faucher-Giguère et al. (2009) that heats and ionizes the gas in an ionization equilibrium approximation.”
The cosmic baryon cycle and galaxy mass assembly in the FIRE simulations (2016, methodology): “We include radiative cooling from primordial gas (Katz et al. 1996) in the presence of a uniform photo-ionizing background (Faucher-Giguère et al. 2009), as well as metal-line (Wiersma et al. 2009), fine-structure, and molecular cooling processes.”
FIRE-2 simulations: physics versus numerics in galaxy formation (2017, methodology): “The relevant ionization states are tabulated from CLOUDY simulations including the effects of uniform but redshift-dependent background (from Faucher-Giguère et al. 2009) together with local radiation sources (every star particle is treated as a source; see the feedback description below).”
Quenching and ram pressure stripping of simulated Milky Way satellite galaxies (2017, background): “…the formation of black holes and feedback from active galactic nuclei (Springel et al. 2005a; Marinacci et al. 2014; Grand et al. 2017); and a spatially uniform but time varying UV background that completes reionization at redshift six (Faucher-Giguère et al. 2009; Vogelsberger et al. 2013).”
The origin and evolution of the galaxy mass–metallicity relation (2015, methodology): “At each timestep, the ionization states and cooling rates are determined from a compilation of CLOUDY runs, including a uniform but redshift-dependent photoionizing background tabulated in Faucher-Giguère et al. (2009), and photo-ionizing and photo-electric heating from local sources.”
BREATHING FIRE: HOW STELLAR FEEDBACK DRIVES RADIAL MIGRATION, RAPID SIZE FLUCTUATIONS, AND POPULATION GRADIENTS IN LOW-MASS GALAXIES (2015, methodology): “We include ionization and heating from a redshift-dependent ultraviolet background computed in Faucher-Giguère et al. (2009) and estimate self-shielding in dense gas via an on-the-fly local Jeans-length approximation.”
The first ultraviolet quasar-stacked spectrum at z ≃ 2.4 from WFC3 (2015, methodology): “Quasars are relevant (maybe even the dominant) sources of ionizing photons that determine the ionization state and the temperature of the z ∼ 3 IGM (e.g. Haardt & Madau 1996, 2012; Meiksin & White 2003; Faucher-Giguère et al. 2009).”
Galaxies on FIRE (Feedback In Realistic Environments): stellar feedback explains cosmologically inefficient star formation (2013, methodology): “…rates are tabulated from a compilation of CLOUDY runs, including the effect of a uniform but redshift-dependent photoionizing background computed in Faucher-Giguère et al. (2009), together with local sources of photo-ionizing and photo-electric heating (described below with the relevant feedback…”
Sweating the small stuff: simulating dwarf galaxies, ultra-faint dwarf galaxies, and their own tiny satellites (2015, methodology): “Our simulations use an ambient ionizing UV background from Faucher-Giguère et al. (2009), which starts at z = 10.65 and completes reionization by z ' 6.”
Vertical disc heating in Milky Way-sized galaxies in a cosmological context (2015, methodology): “Following the model of Faucher-Giguère et al. (2009), a spatially uniform UV background field is included, which completes reionization at redshift z ∼ 6.”
NEW CONSTRAINTS ON COSMIC REIONIZATION FROM THE 2012 HUBBLE ULTRA DEEP FIELD CAMPAIGN (2013, background): “For a detailed discussion, see Furlanetto & Oh (2005); Faucher-Giguère et al. (2009); Kuhlen & Faucher-Giguère (2012).”