The z=9-10 galaxy population in the Hubble Frontier Fields and CLASH surveys: the z=9 luminosity function and further evidence for a smooth decline in ultraviolet luminosity density at z ≥ 8

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 a parts per thousand integral 130 arcmin(2), 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. sigma(160) > 30 AB mag for HFF and sigma(160) > 28.8 AB mag for CLASH in 0.5-arcsec apertures). We unveil a sample of 33 galaxy candidates at z(phot) a parts per thousand yen 8.4, five of which have primary photometric redshift solutions in the range 9.6 < z(phot) < 11.2. The improved statistics and reduced cosmic variance provided by our new sample allows a more accurate determination of the ultraviolet (UV)-selected galaxy luminosity function (LF) at z a parts per thousand integral 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 a parts per thousand integral 2 drop in density, or a dimming of a parts per thousand integral 0.5 mag in M-a