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

R. A. A. Bowler; J. S. Dunlop; R. J. McLure; D. J. McLeod

doi:10.1093/mnras/stw3296

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arXiv · 1605.05325

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

R. A. A. Bowler·J. S. Dunlop·R. J. McLure·D. J. McLeod

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Abstract

We present new Hubble Space Telescope/Wide Field Camera 3 imaging of 25 extremely luminous (-23.2 < M_ UV < -21.2) Lyman-break galaxies (LBGs) at z ~ 7. The sample was initially selected from 1.65 deg^2 of ground-based imaging in the UltraVISTA/COSMOS and UDS/SXDS fields, and includes the extreme Lyman-alpha 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 (EW_0(H_beta + [OIII]) > 600A). We find that irregular, multiple-component morphologies suggestive of clumpy or merging systems are common (f_multi > 0.4) in bright z ~ 7 galaxies, and ubiquitous at the very bright end (M_UV < -22.5). The galaxies have half-light radii in the range r_1/2 ~ 0.5-3 kpc. The size measurements provide the first determination of the size-luminosity relation at z ~ 7 that extends to M_UV ~ -23. We find the relation to be steep with r_1/2 ~ L^1/2. Excluding clumpy, multi-component 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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R. A. A. Bowler, J. S. Dunlop, R. J. McLure, D. J. McLeod. 2016-12-19. Unveiling the nature of bright z ~ 7 galaxies with the Hubble Space Telescope. https://doi.org/10.1093/mnras%2Fstw3296

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