CANDELS: THE CONTRIBUTION OF THE OBSERVED GALAXY POPULATION TO COSMIC REIONIZATION

By S. Finkelstein, C. Papovich, R. Ryan, A. Pawlik, Mark Dickinson, H. Ferguson, K. Finlator, A. Koekemoer, M. Giavalisco, A. Cooray and 5 more. 2012

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We present measurements of the specific ultraviolet luminosity density from a sample of 483 galaxies at 6 ≲ z ≲ 8. These galaxies were selected from new deep near-infrared Hubble Space Telescope imaging from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey, Hubble UltraDeep Field 2009, and Wide Field Camera 3 Early Release Science programs. We investigate the contribution to reionization from galaxies that we observe directly, thus sidestepping the uncertainties inherent in complementary studies that have invoked assumptions regarding the intrinsic shape or the faint-end cutoff of the galaxy ultraviolet (UV) luminosity function. Due to our larger survey volume, wider wavelength coverage, and updated assumptions about the clumping of gas in the intergalactic medium (IGM), we find that the observable population of galaxies can sustain a fully reionized IGM at z = 6, if the average ionizing photon escape fraction (fesc) is ∼30%. Our result contrasts with a number of previous studies that have measured UV luminosity densities at these redshifts that vary by a factor of five, with many concluding that galaxies could not complete reionization by z = 6 unless a large population of galaxies fainter than the detection limit were invoked, or extremely high values of fesc were present. The specific UV luminosity density from our observed galaxy samples at z = 7 and 8 is not sufficient to maintain a fully reionized IGM unless fesc > 50%. We examine the contribution from galaxies in different luminosity ranges and find that the sub-L* galaxies we detect are stronger contributors to the ionizing photon budget than the L > L* population, unless fesc is luminosity dependent. Combining our observations with constraints on the emission rate of ionizing photons from Lyα forest observations at z = 6, we find that we can constrain fesc < 34% (2σ) if the observed galaxies are the only contributors to reionization, or <13% (2σ) if the luminosity function extends to a limiting magnitude of MUV = −13. These escape fractions are sufficient to sustain an ionized IGM by z = 6. Current constraints on the high-redshift galaxy population imply that the volume ionized fraction of the IGM, while consistent with unity at z ⩽ 6, appears to drop at redshifts not much higher than 7, consistent with a number of complementary reionization probes. If faint galaxies dominated the ionizing photon budget at z = 6–7, future extremely deep observations with the James Webb Space Telescope will probe deep enough to directly observe them, providing an indirect constraint on the global ionizing photon escape fraction.

Subfields: Astronomy and Astrophysics, Electrical and Electronic Engineering, Instrumentation

View Paper: https://www.semanticscholar.org/paper/4ee3dc2c7b5d80c23511b152e493c15e3550bb67

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Citations in the corpus

PROBING THE DAWN OF GALAXIES AT z ∼ 9–12: NEW CONSTRAINTS FROM HUDF12/XDF AND CANDELS DATA (2013, background): “…21218, USA 7 University of California, Riverside, 900 University Ave, Riverside, CA 92507, USA † Hubble Fellow Bradley et al. 2012; Yan et al. 2011; Finkelstein et al. 2012; Grazian et al. 2012) From these samples it has become clear that the buildup of galaxies during the first Gyr was a…”
A deep ALMA image of the Hubble Ultra Deep Field (2016, methodology): “The key dataset which defined the area that we aimed to cover with the ALMA 1.3-mm mosaic is the ultra-deep nearinfrared imaging of the HUDF obtained with WFC3/IR on HST via the UDF09 (e.g. Bouwens et al. 2010; McLure et al. 2010; Oesch et al. 2010; Finkelstein et al. 2010, 2012; Bunker c© ???”
The Dearth of z ∼ 10 Galaxies in All HST Legacy Fields—The Rapid Evolution of the Galaxy Population in the First 500 Myr (2017, methodology): “…out to z ∼ 8, large galaxy samples have now been identified and used for the study of galaxy build up (e.g. Bouwens et al. 2011b, 2015; Bradley et al. 2014; Finkelstein et al. 2012a; Schenker et al. 2013; McLure et al. 2013; Schmidt et al. 2014; Barone-Nugent et al. 2014; Stefanon et al. 2017b).”
THE RELATION BETWEEN STAR FORMATION RATE AND STELLAR MASS FOR GALAXIES AT 3.5 ⩽ z ⩽ 6.5 IN CANDELS (2014, background): “Finkelstein et al. (2012a) concluded that if galaxies are the main contributors to reionization, then the escape fraction must be fesc < 0.34, or fesc < 0.13 (2σ) at z ∼ 6 if the luminosity function extends to fainter galaxies than those observed, in order for the inferred ionization from galaxies…”
The mass evolution of the first galaxies: stellar mass functions and star formation rates at 4 < z < 7 in the CANDELS GOODS-South field (2014, methodology): “Despite these degeneracies, it has been shown that one can reliably measure the UV continuum slope, β (Finkelstein et al. 2012a; Rogers et al. 2013).”
REIONIZATION AFTER PLANCK: THE DERIVED GROWTH OF THE COSMIC IONIZING EMISSIVITY NOW MATCHES THE GROWTH OF THE GALAXY UV LUMINOSITY DENSITY (2015, background): “…universe (e.g., Choudhury & Ferrara 2006; Bolton & Haehnelt 2007; Oesch et al. 2009; Trenti et al. 2010; Alvarez et al. 2012; Bouwens et al. 2012a; Finkelstein et al. 2012a; Haardt & Madau 2012 [HM12]; Kuhlen & FaucherGiguère 2012 [KF12]; Shull et al. 2012; Robertson et al. 2013 [R13], 2015…”
Cool Gas in High-Redshift Galaxies (2013, background): “…rise during cosmic reionization from z ∼ 10 to 6 (e.g. Bouwens et al. 2011b; Bouwens et al. 2012, Coe et al. 2013), corresponding to the epoch when light from the first galaxies reionizes the neutral intergalactic medium (IGM) that pervaded the Universe (Fan et al. 2006, Finkelstein et al. 2012).”
Conditions for Reionizing the Universe with a Low Galaxy Ionizing Photon Escape Fraction (2019, methodology): “There are, however, large uncertainties; thus, until recently, most studies assumed a value of ξion∼25.2, expected from modestly metal-poor but otherwise normal single-star population models (e.g., Finkelstein et al. 2012a; Robertson et al. 2015).”
The Evolution of the Intergalactic Medium (2015, methodology): “The curved bands in the righthand panel of www.annualreviews.org • intergalactic medium 29 Figure 10 show the estimated photon emissivity from the observed galaxies as a function of their fesc, from Finkelstein et al. (2012a); see also Bouwens et al. (2015a).”
THE 2012 HUBBLE ULTRA DEEP FIELD (UDF12): OBSERVATIONAL OVERVIEW (2012, background): “…slopes and stellar populations of these early star-forming galaxies at z∼ 7− 8 (Bouwens et al. 2009, 2010, 2012, Ono et al. 2010, Bunker et al. 2010, Finkelstein et al. 2010, 2012b,a, Yan et al. 2011b,a, McLure et al. 2010, 2011, Grazian et al. 2011, 2012, Bradley et al. 2012, Dunlop et al.…”
Detection of high Lyman continuum leakage from four low-redshift compact star-forming galaxies (2016, background): “On the other hand, Finkelstein et al. (2012, 2015) estimated fesc(LyC) < 13 % at z =6 if the luminosity function of galaxies extends to MUV ∼ −13.”
Fluctuating feedback-regulated escape fraction of ionizing radiation in low-mass, high-redshift galaxies (2017, background): “−13 (see also Kuhlen & Faucher-Giguère 2012; Finkelstein et al. 2012) to simultaneously match constraints on the reionization history and the Thomson optical depth.”
The birth of a galaxy – III. Propelling reionization with the faintest galaxies (2014, background): “Recently, a few groups (Finkelstein et al. 2012; Kuhlen & Faucher-Giguère 2012; Robertson et al. 2013) have explored this question among other variations in their reionization models.”
Faint AGNs at z > 4 in the CANDELS GOODS-S field: looking for contributors to the reionization of the Universe (2015, background): “%) are needed to make the star forming galaxy population a major contributor to the reionization (e.g. Finkelstein et al. (2012), Robertson et al. (2013)).”
THE EVOLUTION OF THE GALAXY REST-FRAME ULTRAVIOLET LUMINOSITY FUNCTION OVER THE FIRST TWO BILLION YEARS (2014, methodology): “…to sustain an ionized IGM by z ~ 6, and perhaps as high as z = 7–8, if one assumes that galaxies at least 5 mag below the detection limit of HST exist (e.g., Finkelstein et al. 2012a; Robertson et al. 2013); however, the unknown ionizing photon escape fraction is a major systematic uncertainty.”
LENS MODELS AND MAGNIFICATION MAPS OF THE SIX HUBBLE FRONTIER FIELDS CLUSTERS (2014, background): “…Institute, Baltimore, MD, USA 7 Institute for Astronomy, University of Hawaii, 2680 Wood- lawn Drive, Honolulu, HI 96822, USA the first galaxies to have formed after the Big Bang at z > 8, the factories that formed the first stars responsible for reionizing the universe (Finkelstein et al. 2012).”
The Universe Is Reionizing at z ∼ 7: Bayesian Inference of the IGM Neutral Fraction Using Lyα Emission from Galaxies (2017, background): “…are likely the primary sources of reionizing photons (e.g., Lehnert & Bremer 2003; Bouwens et al. 2003; Yan & Windhorst 2004; Bunker et al. 2004; Finkelstein et al. 2012a; Robertson et al. 2013; Schmidt cmason@astro.ucla.edu et al. 2014), though a contribution from AGN cannot be excluded…”