ARE ULTRA-FAINT GALAXIES AT z = 6–8 RESPONSIBLE FOR COSMIC REIONIZATION? COMBINED CONSTRAINTS FROM THE HUBBLE FRONTIER FIELDS CLUSTERS AND PARALLELS

By H. Atek, J. Richard, M. Jauzac, Jean-Paul Kneib, P. Natarajan, M. Limousin, Daniel Schaerer, E. Jullo, H. Ebeling, E. Egami and 1 more. 2015

139 citations recorded by the source corpus.

We use deep Hubble Space Telescope imaging of the Frontier Fields to accurately measure the galaxy rest-frame ultraviolet luminosity function (UV LF) in the redshift range z ∼ 6–8. We combine observations in three lensing clusters, A2744, MACS 0416, and MACS 0717, and their associated parallel fields to select high-redshift dropout candidates. We use the latest lensing models to estimate the flux magnification and the effective survey volume in combination with completeness simulations performed in the source plane. We report the detection of 227 galaxy candidates at z = 6–7 and 25 candidates at z ∼ 8. While the total survey area is about 4 arcmin2 in each parallel field, it drops to about 0.6–1 arcmin2 in the cluster core fields because of the strong lensing. We compute the UV LF at z ∼ 7 using the combined galaxy sample and perform Monte Carlo simulations to determine the best-fit Schechter parameters. We are able to reliably constrain the LF down to an absolute magnitude of MUV = −15.25, which corresponds to 0.005 L⋆. More importantly, we find that the faint-end slope remains steep down to this magnitude limit with &agr; = − 2.04 − 0.17 + 0.13 . ?> We find a characteristic magnitude of M ⋆ = − 20.89 − 0.72 + 0.60 ?> and log(ϕ⋆) = − 3.54 − 0.45 + 0.48 . ?> Our results confirm the most recent results in deep blank fields but extend the LF measurements more than two magnitudes deeper. The UV LF at z ∼ 8 is not very well constrained below MUV = −18 owing to the small number statistics and incompleteness uncertainties. To assess the contribution of galaxies to cosmic reionization, we derive the UV luminosity density at z ∼ 7 by integrating the UV LF down to an observational limit of MUV = −15. We show that our determination of log(ρUV) = 26.2 ± 0.13 (erg s−1 Hz−1 Mpc−3) can be sufficient to maintain reionization with an escape fraction of ionizing radiation of fesc = 10%–15%. Future Hubble Frontier Fields observations will certainly improve the constraints on the UV LF at the epoch of reionization, paving the way to more ambitious programs using cosmic telescopes with the next generation of large aperture telescopes such as the James Webb Space Telescope and the European Extremely Large Telescope.

Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/2ae2e6c81b98a5adbf61ddbc7315c05c48c1e4a6

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In Astronomy and Astrophysics

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

In Atomic and Molecular Physics, and Optics

1. G. Illingworth
2. R. Bouwens
3. Richard S. Ellis
4. J. Lotz
5. C. Conroy
6. J. Richard
7. R. Livermore
8. S. Finkelstein

In Instrumentation

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

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): “The best-fit φ∗ and luminosity density that Atek et al. (2015) estimate to −15 mag, i.e., ∼ 1026.20±0.13 ergs s−1 Hz−1 Mpc−3, is ∼0.18 dex lower than what we find.”
• Directly Observing the Galaxies Likely Responsible for Reionization (2016, background): “M 12.5UV ) than previous work with these data (Atek et al. 2015a).”
• Fluctuating feedback-regulated escape fraction of ionizing radiation in low-mass, high-redshift galaxies (2017, background): “This point is strengthened by the recent observational constraints on the faint end of the UV LF at high redshift (see for example Atek et al. 2015), showing no cut-off down to magnitude MUV .”
• The Universe Is Reionizing at z ∼ 7: Bayesian Inference of the IGM Neutral Fraction Using Lyα Emission from Galaxies (2017, methodology): “…draw a realistic sample of LBGs at z ∼ 7 from the Mason et al. (2015) UV luminosity function model (which is consistent with all observations, including new deep data from the Hubble Frontier Fields at z∼> 7 e.g., Atek et al. 2015b; McLeod et al. 2016; Livermore et al. 2017; Bouwens et al. 2017a).”
• The THESEUS space mission concept: science case, design and expected performances (2017, background): “Even though some constraints on fainter galaxies can be obtained through observations of lensing clusters (see, e.g., Atek et al., 2015; Vanzella et al., 2017b,a), which will be improved further by JWST, simulations suggest star formation was still likely occurring in considerably fainter systems…”
• Dust in the Reionization Era: ALMA Observations of a z = 8.38 Gravitationally Lensed Galaxy (2017, background): “By harnessing the magnification of a foreground massive cluster, galaxies of more representative luminosities can be probed (e.g. Laporte et al. 2014, Laporte et al. 2016, Coe et al. 2015, Atek et al. 2015).”
• Full-data Results of Hubble Frontier Fields: UV Luminosity Functions at z ∼ 6–10 and a Consistent Picture of Cosmic Reionization (2017, methodology): “(1)Atek et al. (2014), (2)Atek et al. (2015a), (3)Coe et al. (2015), (4)Laporte et al. (2014), (5)Laporte et al. (2015), (6)Laporte et al. (2016), (7)Livermore et al. (2017), (8)McLeod et al. (2016), (9)Oesch et al. (2015) (10)Zheng et al. (2014), (11)Zitrin et al. (2014)”
• The extreme faint end of the UV luminosity function at z ∼ 6 through gravitational telescopes: a comprehensive assessment of strong lensing uncertainties (2018, background): “A more detailed review of all the potential interlopers is given in Atek et al. (2015a).”
• The Dearth of z ∼ 10 Galaxies in All HST Legacy Fields—The Rapid Evolution of the Galaxy Population in the First 500 Myr (2017, background): “Several authors have developed comparable techniques to deal with the ICL (e.g. Atek et al. 2015; Merlin et al. 2016; Bouwens et al. 2017b; Livermore et al. 2017).”
• The Frontier Fields: Survey Design and Initial Results (2016, background): “The first Frontier Fields observations have already probed galaxies during the epoch of reionization to intrinsic luminosities fainter than any previously seen (e.g. Livermore, Finkelstein, & Lotz 2016; Castellano et al. 2016; Atek et al. 2015; Laporte et al. 2015; Zitrin et al. 2014).”
• Rapid Reionization by the Oligarchs: The Case for Massive, UV-bright, Star-forming Galaxies with High Escape Fractions (2019, background): “…to “democratic” reionization that is dominated by copious faint sources that lie at MUV>−18 and might potentially have high escape fractions (e.g., Oesch et al. 2009; Bouwens et al. 2011; Wise et al. 2014; Atek et al. 2015; Anderson et al. 2017; Livermore et al. 2017; Finkelstein et al. 2019).”
• Great Optically Luminous Dropout Research Using Subaru HSC (GOLDRUSH). I. UV Luminosity Functions at $z \sim 4-7$ Derived with the Half-Million Dropouts on the 100 deg$^2$ Sky (2017, background): “…sources with the Hubble Frontier Fields (HFF) project, which takes advantage of the gravitational lens magnification effects of galaxy clusters (Ishigaki et al. 2015; Atek et al. 2015; Kawamata et al. 2016; Castellano et al. 2016; McLeod et al. 2016; Livermore et al. 2017; Ishigaki et al. 2017).”
• The bolometric quasar luminosity function at z = 0–7 (2020, background): “Bowler et al. 2015; Bouwens et al. 2015; Parsa et al. 2016; Finkelstein 2016; Mehta et al. 2017; Atek et al. 2015, 2018; Ishigaki et al. 2018) and theoretical studies (Jaacks et al. 2012; Tacchella et al. 2013; Mason et al. 2015; Wilkins et al. 2017; Tacchella et al. 2018; Yung et al. 2018).”
• Radiation Backgrounds at Cosmic Dawn: X-Rays from Compact Binaries (2016, unknown): “Recent results on the z ∼ 7 LF derived from magnified sources behind lensing clusters have indicated a steep faint-end slope, α = −2.04, which extends down to Mlim = −15.25, corresponding to 0.005L∗ (Atek et al. 2015).”
• GALAXY PROPERTIES AND UV ESCAPE FRACTIONS DURING THE EPOCH OF REIONIZATION: RESULTS FROM THE RENAISSANCE SIMULATIONS (2016, result): “We have presented the evolution of galaxy LFs of the Renaissance Simulations in O’Shea et al. (2015), but we reproduce the LF in the Normal region at z=12.5, now comparing it to the latest results from the Frontier Fields (Atek et al. 2015; Livermore et al. 2016) and the Bouwens et al. (2015) redshi”