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Are ultra-faint galaxies at z = 6–8 responsible for cosmic reionization? Combined constraints from the Hubble Frontier Fields clusters and parallels

Atek, H.; Richard, J.; Jauzac, M.; Kneib, J.-P.; Natarajan, P.; Limousin, M.; Schaerer, D.; Jullo, E.; Ebeling, H.; Egami, E.; Clément, B.

Are ultra-faint galaxies at z = 6–8 responsible for cosmic reionization? Combined constraints from the Hubble Frontier Fields clusters and parallels Thumbnail


Authors

H. Atek

J. Richard

J.-P. Kneib

P. Natarajan

M. Limousin

D. Schaerer

E. Jullo

H. Ebeling

E. Egami

B. Clément



Abstract

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 Lsstarf. More importantly, we find that the faint-end slope remains steep down to this magnitude limit with $\alpha =-{2.04}_{-0.17}^{+0.13}.$ We find a characteristic magnitude of ${M}^{\star }=-{20.89}_{-0.72}^{+0.60}$ and log(phgrsstarf) = $-{3.54}_{-0.45}^{+0.48}.$ 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.

Citation

Atek, H., Richard, J., Jauzac, M., Kneib, J., Natarajan, P., Limousin, M., …Clément, B. (2015). Are ultra-faint galaxies at z = 6–8 responsible for cosmic reionization? Combined constraints from the Hubble Frontier Fields clusters and parallels. Astrophysical Journal, 814(1), Article 69. https://doi.org/10.1088/0004-637x/814/1/69

Journal Article Type Article
Acceptance Date Oct 8, 2015
Online Publication Date Nov 17, 2015
Publication Date Nov 17, 2015
Deposit Date Feb 10, 2016
Publicly Available Date Feb 11, 2016
Journal Astrophysical Journal
Print ISSN 0004-637X
Electronic ISSN 1538-4357
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 814
Issue 1
Article Number 69
DOI https://doi.org/10.1088/0004-637x/814/1/69
Keywords Dark ages, reionization, first stars, Galaxies: high-redshift, Galaxies: luminosity function, mass function, Gravitational lensing: strong.
Public URL https://durham-repository.worktribe.com/output/1391856

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Copyright Statement
© 2015. The American Astronomical Society. All rights reserved.






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