Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A Hubble & Spitzer Space Telescope Survey for Gravitationally-Lensed
  Galaxies: Further Evidence for a Significant Population of Low Luminosity
  Galaxies beyond Redshift Seven   We present the results of a systematic search for gravitationally-lensed
continuum Lyman break `drop-outs' beyond a redshift 7 conducted via very deep
imaging through six foreground clusters undertaken with the Hubble and Spitzer
Space Telescopes. The survey has yielded 10 z-band and 2 J-band drop-out
candidates to photometric limits of J_110~=26.2 AB (5sigma). Taking into
account the magnifications afforded by our clusters (1-4 magnitudes), we probe
the presence of z>7 sources to unlensed limits of J_{110}~=30 AB, fainter than
those charted in the Hubble Ultradeep Field. To verify the fidelity of our
candidates we conduct a number of tests for instrumental effects which would
lead to spurious detections, and carefully evaluate the likelihood of
foreground contamination by considering photometric uncertainties in the
drop-out signature, the upper limits from stacked IRAC data and the statistics
of multiply-imaged sources. Overall, we conclude that we can expect about half
of our sample of z-band drop-outs are likely to be at high redshift. An
ambitious infrared spectroscopic campaign undertaken with the NIRSPEC
spectrograph at the WM Keck Observatory for seven of the most promising
candidates failed to detect any Lyman-alpha emission highlighting the challenge
of making further progress in this field. While the volume density of high
redshift sources will likely remain uncertain until more powerful facilities
are available, our data provides the first potentially interesting constraints
on the UV luminosity function at z~=7.5 at intrinsically faint limits. We
discuss the implications of our results in the context of the hypothesis that
the bulk of the reionizing photons in the era 7<z<12 arise in low luminosity
galaxies undetected by conventional surveys.

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The categories of this paper are: comp-gas
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The categories of this paper are: mtrl-th
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The categories of this paper are: funct-an
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The categories of this paper are: hep-ex
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The categories of this paper are: math-ph
3
The categories of this paper are: physics
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The categories of this paper are: dg-ga
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The categories of this paper are: nlin
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The categories of this paper are: stat
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The categories of this paper are: eess
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The categories of this paper are: acc-phys
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The categories of this paper are: hep-lat
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The categories of this paper are: bayes-an
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The categories of this paper are: hep-ph
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The categories of this paper are: gr-qc
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The categories of this paper are: q-fin