http://arxiv.org/abs/1602.05199
We present the results of a search for z=9-10 galaxies within the first 8 pointings of the Hubble Frontier Fields (HFF) (4 clusters plus 4 parallel fields) and 20 cluster fields from the CLASH survey. Combined with our previous analysis of the Hubble Ultra-Deep field (HUDF), we have now completed a search for z=9-10 galaxies over ~130 sq. arcmin, across 29 HST WFC3/IR pointings. As in our recent study of the first two HFF fields, we confine our primary search for high-redshift candidates in the HFF imaging to the uniformly deep (i.e. sigma_160>30 AB mag in 0.5-arcsec diameter apertures), relatively low magnification regions. In the CLASH fields our search was confined to uniformly deep regions where sigma_160>28.8 AB mag. Our SED fitting analysis unveils 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<11.2. By calculating a de-lensed effective volume for each candidate, the improved statistics and reduced cosmic variance provided by our new sample allows a more accurate determination of the UV-selected galaxy luminosity function (LF) at z~9. Our new results strengthen our previous conclusion that the LF appears to evolve smoothly from z=8 to z=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, based on our new sample, we are able to place initial constraints on the z=10 LF, finding that the number density at M_1500 ~ -19.7 is log(phi) = -4.1 (+0.2,-0.3), a factor of ~2 lower than at z=9. Finally, we use our new results to re-visit the issue of the decline in UV luminosity density at z>=8. We conclude that the data continue to support a smooth decline in rho_UV over the redshift interval 6<z<10, in agreement with simple models of early galaxy evolution driven by the growth in the underlying dark matter halo mass function.
D. McLeod, R. McLure and J. Dunlop
Thu, 18 Feb 16
34/44
Comments: Submitted to MNRAS, 13 pages, 11 figures
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