Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 450, Issue 3, Pages 3032-3044Publisher
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stv780
Keywords
galaxies: evolution; galaxies: formation; galaxies: high-redshift
Categories
Funding
- European Research Council
- EC FP7 SPACE project ASTRODEEP [312725]
- National Science Foundation [1228509]
- Space Telescope Science Institute [HST-GO-12498.01-A]
- NASA [NAS5-26555, 1407]
- ESO [092.A-0472]
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We present the results of a new search for galaxies at redshift z a parts per thousand integral 9 in the first two Hubble Frontier Fields with completed HST WFC3/IR and ACS imaging. To ensure robust photometric redshift solutions, and to minimize incompleteness, we confine our search to objects with H-160 < 28.6 (AB mag), consider only image regions with an rms noise sigma(160) > 30 mag (within a 0.5-arcsec diameter aperture), and insist on detections in both H-160 and J(140). The result is a survey covering an effective area (after accounting for magnification) of 10.9 arcmin(2), which yields 12 galaxies at 8.4 < z < 9.5. Within the Abell-2744 cluster and parallel fields, we confirm the three brightest objects reported by Ishigaki et al., but recover only one of the four z > 8.4 sources reported by Zheng et al. In the MACSJ0416.1-240 cluster field, we report five objects, and explain why each of these eluded detection or classification as z a parts per thousand integral 9 galaxies in the published searches of the shallower CLASH data. Finally, we uncover four z a parts per thousand integral 9 galaxies from the MACSJ0416.1-240 parallel field. Based on the published magnification maps, we find that only one of these 12 galaxies is likely boosted by more than a factor of 2 by gravitational lensing. Consequently, we are able to perform a fairly straightforward reanalysis of the normalization of the z a parts per thousand integral 9 UV galaxy luminosity function as explored previously in the HUDF12 programme. We conclude that the new data strengthen the evidence for a continued smooth decline in UV luminosity density (and hence star formation rate density) from z a parts per thousand integral 8 to 9, contrary to recent reports of a marked drop-off at these redshifts. This provides further support for the scenario in which early galaxy evolution is sufficiently extended to explain cosmic reionization.
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