LOWER-LUMINOSITY GALAXIES COULD REIONIZE THE UNIVERSE: VERY STEEP FAINT-END SLOPES TO THE UV LUMINOSITY FUNCTIONS AT z ⩾ 5–8 FROM THE HUDF09 WFC3/IR OBSERVATIONS

By R. Bouwens, G. Illingworth, P. Oesch, M. Trenti, I. Labbé, M. Franx, M. Stiavelli, C. Carollo, P. V. van Dokkum, D. Magee. 2011

227 citations recorded by the source corpus.

The HUDF09 data are the deepest near-IR observations ever, reaching to 29.5 mag. Luminosity functions (LFs) from these new HUDF09 data for 132 z ∼ 7 and z ∼ 8 galaxies are combined with new LFs for z ∼ 5–6 galaxies and the earlier z ∼ 4 LF to reach to very faint limits (<0.05  L*z = 3). The faint-end slopes α are steep: −1.79 ± 0.12 (z ∼ 5), −1.73 ± 0.20 (z ∼ 6), −2.01 ± 0.21 (z ∼ 7), and −1.91 ± 0.32 (z ∼ 8). Slopes α ≲ −2 lead to formally divergent UV fluxes, though galaxies are not expected to form below ∼  − 10 AB mag. These results have important implications for reionization. The weighted mean slope at z ∼ 6-8 is −1.87 ± 0.13. For such steep slopes, and a faint-end limit of −10 AB mag, galaxies provide a very large UV ionizing photon flux. While current results show that galaxies can reionize the universe by z ∼ 6, matching the Thomson optical depths is more challenging. Extrapolating the current LF evolution to z > 8, taking α to be −1.87 ± 0.13 (the mean value at z ∼ 6-8), and adopting typical parameters, we derive Thomson optical depths of 0.061+0.009− 0.006. However, this result will change if the faint-end slope α is not constant with redshift. We test this hypothesis and find a weak, though uncertain, trend to steeper slopes at earlier times (dα/dz ∼ −0.05 ± 0.04) that would increase the Thomson optical depths to 0.079+0.063− 0.017, consistent with recent WMAP estimates (τ = 0.088 ± 0.015). It may thus not be necessary to resort to extreme assumptions about the escape fraction or clumping factor. Nevertheless, the uncertainties remain large. Deeper WFC3/IR+ACS observations can further constrain the UV ionizing flux from faint galaxies.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/a2ba5c3a2aecc3df5c397167e9418ea44b9d88f5

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In Astronomy and Astrophysics

1. Richard S. Ellis
2. L. Hernquist
3. P. V. van Dokkum
4. P. Hopkins
5. M. Franx
6. R. Bouwens
7. P. Oesch
8. G. Illingworth

In Instrumentation

1. Richard S. Ellis
2. P. V. van Dokkum
3. M. Franx
4. R. Bouwens
5. G. Illingworth
6. P. Oesch
7. I. Labbé
8. J. Dunlop

Citations in the corpus

• CLASH: THREE STRONGLY LENSED IMAGES OF A CANDIDATE z ≈ 11 GALAXY (2012, methodology): “If these luminosity functions can be extrapolated to z & 10, then low luminosity galaxies (MUV fainter than −16 AB) could have reionized the universe (Bouwens et al. 2012a; Kuhlen & Faucher-Giguère 2012), assuming a sufficient fraction of their UV photons could escape their host galaxies to the…”
• UV LUMINOSITY FUNCTIONS AT REDSHIFTS z ∼ 4 TO z ∼ 10: 10,000 GALAXIES FROM HST LEGACY FIELDS (2014, methodology): “However, as subsequent research has shown (Wilkins et al. 2011; Bouwens et al. 2012, 2013; Finkelstein et al. 2012; Willott et al. 2013; Rogers et al. 2013), the most luminous z ∼ 6 galaxies have moderately red UV -continuum slopes β ∼ −1.5.”
• Cool Gas in High-Redshift Galaxies (2013, background): “…at near–IR wavelengths, and narrow band near–IR surveys, are now systematically detecting galaxies at z ∼ 6 to 10, corresponding to the tail–end of cosmic reionization when the Universe was less than 1Gyr old (Bouwens et al. 2012a,b; Pentericci et al. 2011, Bradac et al. 2012; Coe et al. 2013).”
• A CENSUS OF STAR-FORMING GALAXIES IN THE Z ∼ 9–10 UNIVERSE BASED ON HST+SPITZER OBSERVATIONS OVER 19 CLASH CLUSTERS: THREE CANDIDATE Z ∼ 9–10 GALAXIES AND IMPROVED CONSTRAINTS ON THE STAR FORMATION RATE DENSITY AT Z ∼ 9.2 (2012, methodology): “Given the observed trends towards bluer UV - continuum slopes β at very high redshifts (e.g., Stanway et al. 2005; Bouwens et al. 2006, 2009, 2012b, 2013b; Finkelstein et al. 2012; Wilkins et al. 2011), we would expect the dust extinction at z ∼ 9-10 to be zero, and therefore apply no dust…”
• The galaxy luminosity function at z ≃ 6 and evidence for rapid evolution in the bright end from z ≃ 7 to 5 (2014, methodology): “Reassuringly, our fits recover the steep faint-end slopes found in previous studies (Bouwens et al. 2012; McLure et al. 2013; Schenker et al. 2013), showing that our measurement of α is not being strongly influenced by any tension in the fitting process.”
• UV-CONTINUUM SLOPES OF >4000 z ∼ 4–8 GALAXIES FROM THE HUDF/XDF, HUDF09, ERS, CANDELS-SOUTH, AND CANDELS-NORTH FIELDS (2013, methodology): “In Figure 9, the observed trends are compared with our z ∼ 7 results from §3, z ∼ 1-6 results from the literature (Labbe et al. 2009; Bouwens et al. 2009; Bouwens et al. 2012), and also with the hydrodynamical simulation results from Finlator et al. (2011).”
• Lyα EMISSION FROM A LUMINOUS z = 8.68 GALAXY: IMPLICATIONS FOR GALAXIES AS TRACERS OF COSMIC REIONIZATION (2015, methodology): “…population has been used to argue that star-forming galaxies played a significant role in completing the reionization of the IGM by redshift z ∼ 6 (e.g. Robertson et al. 2013, 2015; Kuhlen & FaucherGiguère 2012; Bouwens et al. 2012, 2015a; Finkelstein et al. 2012, 2015; Ishigaki et al. 2015).”
• The First Billion Years project: the escape fraction of ionizing photons in the epoch of reionization (2015, background): “…is a key parameter in studies of the contribution of the observed galaxy ∗ E-mail: jppaarde@uni-heidelberg.de population to reionisation (e.g. Bouwens et al. 2012; Robertson et al. 2013), semi-analytic modelling of reionisation (e.g. Choudhury et al. 2009; Pritchard et al. 2010; Santos et…”
• Reionization and the Cosmic Dawn with the Square Kilometre Array (2012, background): “…galaxies to fainter ones requires assumptions about the highly uncertain faint end slope of the luminosity function, leading to debates on whether star forming galaxies can have been responsible for the reionization of the Universe at all (see e.g. Lorenzoni et al. 2011; Bouwens et al. 2012).”
• Fluctuating feedback-regulated escape fraction of ionizing radiation in low-mass, high-redshift galaxies (2017, background): “Several studies showed that these galaxies have bluer UV-continuum slopes than their more massive counterparts (Bouwens et al. 2009, 2012, 2014), with no significant redshift evolution.”
• COSMIC REIONIZATION AFTER PLANCK: COULD QUASARS DO IT ALL? (2015, background): “…only if one extrapolates the steep UV luminosity function well below the observed limits and assumes a globally-averaged absolute escape fraction of Lyman-continuum (LyC) radiation into the early IGM, f̄esc, that exceeds 20% (e.g., Bouwens et al. 2012; Finkelstein et al. 2012; Haardt & Madau 2012).”
• THE MOST LUMINOUS z ∼ 9–10 GALAXY CANDIDATES YET FOUND: THE LUMINOSITY FUNCTION, COSMIC STAR-FORMATION RATE, AND THE FIRST MASS DENSITY ESTIMATE AT 500 Myr (2013, methodology): “Even for other test LFs, such as the z ∼ 9 UV LF estimates from Oesch et al. (2013a) and Bouwens et al. (2012a), only ∼2 sources were expected to be seen in GOODS-N.”
• CONTRASTING GALAXY FORMATION FROM QUANTUM WAVE DARK MATTER, ψDM, WITH ΛCDM, USING PLANCK AND HUBBLE DATA (2015, methodology): “M 17 10lim , z = ~0.5 2.0ion , and = ~f 0.1 0.5esc (Bouwens et al. 2012; Kuhlen & Faucher-Giguère 2012; Schultz et al. 2014; Bozek et al. 2015; Bouwens et al. 2015a; Robertson et al. 2015).”
• A case study of hurdle and generalized additive models in astronomy: the escape of ionizing radiation (2018, background): “…of ion- E-mail: drsouza@ad.unc.edu izing photons, fesc,1 represents a key parameter to probe different reionization scenarios in observational (e.g. Bouwens et al. 2012; Robertson et al. 2013), semi-analytical (e.g. Choudhury, Haehnelt & Regan 2009; Pritchard, Loeb & Wyithe 2010; Santos et al.…”
• THE BRIGHTEST OF REIONIZING GALAXIES SURVEY: CONSTRAINTS ON THE BRIGHT END OF THE z ∼ 8 LUMINOSITY FUNCTION (2012, methodology): “This implies that the total ionizing flux produced by galaxies is sensitive to the exact measure of α (as well as on the extrapolation beyond the detection limit), as shown, for example, in the left panel of Figure 4 of Bouwens et al. (2012).”
• The birth of a galaxy – III. Propelling reionization with the faintest galaxies (2014, background): “…guest on Septem ber 12, 2016 http://m nras.oxfordjournals.org/ nloaded from observed z > 6 galaxy luminosity function (LF) to low luminosities (e.g. Madau, Haardt & Rees 1999; Bouwens et al. 2012a; Fontanot, Cristiani & Vanzella 2012; Haardt & Madau 2012; Shull et al. 2012; Robertson et al. 2013).”
• PROBING THE DAWN OF GALAXIES AT z ∼ 9–12: NEW CONSTRAINTS FROM HUDF12/XDF AND CANDELS DATA (2013, methodology): “These results on the galaxy evolution at z > 8 contrast with the conclusions drawn by several recent papers, who argue that the UV LD evolution at z > 8 is consistent with the lower redshift trends (e.g. Ellis et al. 2013; Coe et al. 2013; Zheng et al. 2012).”