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Unveiling the nature of bright z ≃ 7 galaxies with the Hubble Space Telescope

Bowler, R. A. A. and Dunlop, J. S. and McLure, R. J. and McLeod, D. J. (2017) Unveiling the nature of bright z ≃ 7 galaxies with the Hubble Space Telescope. Monthly Notices of the Royal Astronomical Society, 466 (3). pp. 3612-3635. ISSN 0035-8711. doi:10.1093/mnras/stw3296.

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We present new Hubble Space Telescope/Wide Field Camera 3 (HST/WFC3) imaging of 25 extremely luminous (−23.2 ≤ MUV ≲ −21.2) Lyman-break galaxies (LBGs) at z ≃ 7. The sample was initially selected from 1.65 deg2 of ground-based imaging in the UltraVISTA/COSMOS and UDS/SXDS fields, and includes the extreme Lyman α emitters, ‘Himiko’ and ‘CR7’. A deconfusion analysis of the deep Spitzer photometry available suggests that these galaxies exhibit strong rest-frame optical nebular emission lines (EW0(Hβ + [O III]) > 600 Å). We find that irregular, multiple-component morphologies suggestive of clumpy or merging systems are common (fmulti > 0.4) in bright z ≃ 7 galaxies, and ubiquitous at the very bright end (MUV < −22.5). The galaxies have half-light radii in the range r1/2 ∼ 0.5–3 kpc. The size measurements provide the first determination of the size–luminosity relation at z ≃ 7 that extends to MUV ∼ −23. We find the relation to be steep with r1/2 ∝ L1/2. Excluding clumpy, multicomponent galaxies however, we find a shallower relation that implies an increased star formation rate surface density in bright LBGs. Using the new, independent, HST/WFC3 data we confirm that the rest-frame UV luminosity function at z ≃ 7 favours a power-law decline at the bright end, compared to an exponential Schechter function drop-off. Finally, these results have important implications for the Euclid mission, which we predict will detect >1000 similarly bright galaxies at z ≃ 7. Our new HST imaging suggests that the vast majority of these galaxies will be spatially resolved by Euclid, mitigating concerns over dwarf star contamination.

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Additional Information:© 2017 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2016 December 13. Received 2016 December 12; in original form 2016 May 18.
Issue or Number:3
Record Number:CaltechAUTHORS:20170628-131233779
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:78654
Deposited By: Joy Painter
Deposited On:28 Jun 2017 21:24
Last Modified:15 Nov 2021 17:42

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