Evolution of the Intergalactic Opacity: Implications for the Ionizing Background, Cosmic Star Formation, and Quasar Activity

By C. Faucher-Giguére, A. Lidz, L. Hernquist, M. Zaldarriaga. 2008

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We investigate the implications of the intergalactic opacity for the evolution of the cosmic UV luminosity density and its sources. Our main constraint is our measurement of the Lyα forest opacity at redshifts 2 ⩽ z ⩽ 4.2 from 86 high-resolution quasar spectra. In addition, we impose the requirements that H I must be reionized by z = 6 and He II by z ∼ 3 and consider estimates of the hardness of the ionizing background from H I-to-He II column density ratios. The derived hydrogen photoionization rate is remarkably flat over the Lyα forest redshift range covered. Because the quasar luminosity function is strongly peaked near z ∼ 2, the lack of redshift evolution indicates that star-forming galaxies likely dominate the photoionization rate at z ≳ 3. Combined with direct measurements of the galaxy UV luminosity function, this requires only a small fraction fesc ∼ 0.5% of galactic hydrogen-ionizing photons to escape their source for galaxies to solely account for the entire ionizing background. Under the assumption that the galactic UV emissivity traces the star formation rate, current state-of-the-art observational estimates of the star formation rate density appear to underestimate the total photoionization rate at z ∼ 4 by a factor of ~4, are in tension with recent determinations of the UV luminosity function, and fail to reionize the universe by z ∼ 6 if extrapolated to arbitrarily high redshift. A theoretical star formation history peaking earlier fits the Lyα forest photoionization rate well, reionizes the universe in time, and is in better agreement with the rate of z ∼ 4 gamma-ray bursts observed by Swift. Quasars suffice to doubly ionize helium by z ∼ 3 and likely contribute a nonnegligible and perhaps dominant fraction of the hydrogen-ionizing background at their z ∼ 2 peak.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/75c633008d5e03c324e74f1c1890c2fb13c73f9c

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Citations in the corpus

The bolometric quasar luminosity function at z = 0–7 (2020, methodology): “First, to simplify the calculation, we adopt the "local source" approximation (e.g., Schirber & Bullock 2003; Faucher-Giguère et al. 2008b; Hopkins et al. 2007), which assumes that only ionizing sources with optical depth τeff ≤ 1 contribute to the ionizing background (we will relax this assumption…”
Measurements of the UV background at 4.6 < z < 6.4 using the quasar proximity effect (2010, methodology): “As already discussed this is believed to be the main reason for the discrepancies between estimates of the UVB using the proximity effect and theflux decrement method (Rollinde et al. 2005; Guimarães et al. 2007; Faucher-Giguère et al. 2008) at redshiftz ∼ 2− 4.”
Concordance models of reionization: implications for faint galaxies and escape fraction evolution (2012, methodology): “Models of the ionizing background at intermediate redshifts indicate that star-forming galaxies dominate at z & 3 (Haehnelt et al. 2001; Bolton et al. 2005; Faucher-Giguère et al. 2008a, 2009).”
A DEEP HUBBLE SPACE TELESCOPE SEARCH FOR ESCAPING LYMAN CONTINUUM FLUX AT z ∼ 1.3: EVIDENCE FOR AN EVOLVING IONIZING EMISSIVITY (2010, background): “Recent investigations of the ionizing background at high redshift (Bolton et al. 2005; Becker et al. 2007) note that the Hi–photoionization rate is fairly flat between 2 < z < 4, which implies an increase in the ionizing emissitivity at higher redshifts (Faucher-Giguère et al. 2008).”
A model for cosmological simulations of galaxy formation physics: multi-epoch validation (2013, methodology): “…luminosity functions, the model was calibrated to satisfy the measured mean transmission of the Ly-alpha forest at intermediate redshifts z = 2−4.2 (Faucher-Giguère et al. 2008a,b), published HeII to HI column density ratios, HeII reionisation by z ∼ 3 (McQuinn et al. 2009), and complete HI…”
THE EVOLUTION OF LYMAN LIMIT ABSORPTION SYSTEMS TO REDSHIFT SIX (2010, methodology): “We use the form of the LLS evolution to compute the mean free path for ionizing photons, showing that the present observations decrease this compared with recent analyses (e.g. Faucher-Giguère et al. 2008).”
ESCAPE FRACTION OF IONIZING PHOTONS DURING REIONIZATION: EFFECTS DUE TO SUPERNOVA FEEDBACK AND RUNAWAY OB STARS (2014, background): “…to ionizing photons in both the ultraviolet (UV) and X-ray bands but are generally believed to be sub-dominant to stellar sources (Haehnelt et al. 2001; Wyithe & Loeb 2003; Schirber & Bullock 2003; Faucher-Giguère et al. 2008; Cowie et al. 2009; Willott et al. 2010; Fontanot et al. 2014).”
MODELING THE EXTRAGALACTIC BACKGROUND LIGHT FROM STARS AND DUST (2009, background): “Aside from direct observations, the UV luminosity density at high redshift can be probed with measurements of the photoionization rate from the Lyα forest (Faucher-Giguère et al. 2008a,b).”
A DEFINITIVE SURVEY FOR LYMAN LIMIT SYSTEMS AT z ∼ 3.5 WITH THE SLOAN DIGITAL SKY SURVEY (2009, methodology): “…constrained cosmological parameters such as the primordial power spectrum and the baryonic mass density and astrophysical parameters like the amplitude of the ionizing background (e.g. Rauch 1998; Croft et al. 2002; McDonald et al. 2005; Tytler et al. 2004; Faucher-Giguère et al. 2008b).”
Keeping the Universe ionized: photoheating and the clumping factor of the high-redshift intergalactic medium (2008, background): “…rate based on measurements of the high-redshift (z = 4 − 7) gamma ray burst rate (Yüksel et al. 2008) and measurements of the Lyman-alpha forest opacity at redshifts z ∼ 3 (Faucher-Giguère et al. 2008) indeed suggest z ∼ 6 SFRs that exceed those inferred from UV galaxy counts by factors of a few.”
He ii REIONIZATION AND ITS EFFECT ON THE INTERGALACTIC MEDIUM (2008, methodology): “Bolton et al. (2005), Becker et al. (2007), and especially Faucher-Giguère et al. (2008b) measured the hydrogen photoionization rate (ΓHI) to be flat as a function of redshift using the flux decrement method on 2 < z < 4 HI Lyα forest data and to within a factor of ∼ 2 given by ΓHI(z) = 10 −12 s−1.”
The first ultraviolet quasar-stacked spectrum at z ≃ 2.4 from WFC3 (2015, background): “…stack at z 2.4 from WFC3 4205 et al. 2014), they are likely the only sources responsible for the reionization of He II at z ∼ 3 (Miralda-Escudé, Haehnelt & Rees 2000; Faucher-Giguère et al. 2008; Furlanetto 2009; McQuinn et al. 2009; Haardt & Madau 2012; Compostella, Cantalupo & Porciani 2013).”
ON LYMAN-LIMIT SYSTEMS AND THE EVOLUTION OF THE INTERGALACTIC IONIZING BACKGROUND (2011, methodology): “The near constancy of Γ that is measured at z ≈ 2 − 4 (Bolton & Haehnelt 2007; Faucher-Giguère et al. 2008) puts stringent requirements on the evolution of the total comoving ionizing emissivity owing to this strong scaling, requiring it to be roughly constant.”
Lyα COOLING EMISSION FROM GALAXY FORMATION (2010, background): “At z = 3, for example, the diffuse IGM transmits only ≈ 67% of photons immediately blueward of Lyα and this fraction decreases rapidly with increasing redshift (e.g., Faucher-Giguère et al. 2008d).”
NEW CONSTRAINTS ON COSMIC REIONIZATION FROM THE 2012 HUBBLE ULTRA DEEP FIELD CAMPAIGN (2013, methodology): “…photon production rateṡn = [3.2,3.5,4.3] × 1050 s−1 Mpc−3 at redshiftsz = [4.0,4.2,5.0] inferred by Kuhlen & Faucher-Giguère (2012) from measurements by Faucher-Giguère et al. (2008), Prochaska et al. (2009), and Songaila & Cowie (2010), this maximum likelihood model with evolving fescrecovers…”
RADIATIVE TRANSFER IN A CLUMPY UNIVERSE. IV. NEW SYNTHESIS MODELS OF THE COSMIC UV/X-RAY BACKGROUND (2011, background): “This trend is consistent with the conclusions reached by Bolton & Haehnelt (2007) and Faucher-Giguère et al. (2008a) from empirical measurements of the Lyα forest opacity.”
The Giant Gemini GMOS survey of zem > 4.4 quasars – I. Measuring the mean free path across cosmic time (2014, methodology): “3 1.6 This paper Indirect estimatesb 3.0 ∼100 85 65 Faucher-Giguère et al. (2008c) LLSs and β = 1.39, γ = 1.5 3.5 ∼100 49 20 Songaila & Cowie (2010) LLSs and β = 1.3, γ = 1.94 4.5 ∼60 20 8 Songaila & Cowie (2010) LLSs and β = 1.3, γ = 1.94 Notes.”
INTENSITY MAPPING WITH CARBON MONOXIDE EMISSION LINES AND THE REDSHIFTED 21 cm LINE (2011, background): “These suggest that the total emissivity of ionizing photons at z = 5 − 6 is comparable to the critical value required to keep the Universe ionized (Miralda-Escudè 2003, Bolton & Haehnelt 2005, Faucher-Giguère et al. 2008, McQuinn et al. 2011).”