2016MNRAS.459.3812M

We present the results of a search for z=9-10 galaxies within the first eight pointings of the Hubble Frontier Fields (HFF) survey and 20 cluster fields from the Cluster Lensing And Supernova survey with Hubble (CLASH) survey. Combined with our previous analysis of the Hubble Ultra Deep Field, we have now completed a search for z=9-10 galaxies over ≃ 130 arcmin², spread across 29 Hubble Space Telescope Wide Field Camera 3/IR pointings. We confine our primary search for high-redshift candidates in this imaging to the uniformly deep, relatively low magnification regions (i.e. σ₁₆₀ > 30 AB mag for HFF and σ₁₆₀ > 28.8 AB mag for CLASH in 0.5-arcsec apertures). We unveil a sample of 33 galaxy candidates at z_phot ≥ 8.4, five of which have primary photometric redshift solutions in the range 9.6 z_phot z ≃ 9. Our new results strengthen our previous conclusion that the LF appears to evolve smoothly from z=8 to 9, an evolution which can be equally well modelled by a factor of ≃ 2 drop in density, or a dimming of ≃ 0.5 mag in M^*. Moreover, we are able to place initial constraints on the z=10 LF, finding that the number density at M₁₅₀₀ ≃ -19.7 is log(φ)=-4.1^{+0.2}_{-0.3} , a factor of ≃ 2 lower than at z=9. Finally, we use our new results to revisit the issue of the decline in UV luminosity density (ρ_UV) at z ≥ 8. We conclude that the data continue to support a smooth decline in ρ_UV over the redshift interval 6 z