A Hubble & Spitzer Space Telescope Survey for Gravitationally-Lensed Galaxies: Further Evidence for a Significant Population of Low Luminosity Galaxies beyond Redshift Seven

Abstract

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.

53 pages, 17 figures; Accepted for publication in ApJ. Full version with high resolution figures available at http://astro.caltech.edu/~johan/nicmos/nicmos_accepted.pdf

References in corpus (20)

• Wilkinson Microwave Anisotropy Probe (WMAP) Three Year Results: Implications for Cosmology
• The Hubble Ultra Deep Field
• A Bayesian approach to strong lensing modelling of galaxy clusters
• The End of the Reionization Epoch Probed by Ly-alpha Emitters at z=6.5 in the Subaru Deep Field
• The observed ionization rate of the intergalactic medium and the ionizing emissivity at z >5: Evidence for a photon starved and extended epoch of reionization
• The Direct Detection of Lyman-Continuum Emission from Star-forming Galaxies at z~3
• Combining Strong and Weak Gravitational Lensing in Abell 1689
• A galaxy at a redshift z = 6.96
• Meeting the Cool Neighbors. IX. The Luminosity Function of M7-L8 Ultracool Dwarfs in the Field
• A Cross-Match of 2MASS and SDSS: Newly-Found L and T Dwarfs and an Estimate of the Space Densitfy of T Dwarfs
• Discovery of a Very Bright Strongly-Lensed Galaxy Candidate at z ~ 7.6
• The Stellar Mass Density at z~6 from Spitzer Imaging of i-drop Galaxies
• Intergalactic CIV absorption at redshifts 5.4 to 6
• Rapid Evolution in the Most Luminous Galaxies During the First 900 Million Years
• A Lensing Survey of X-ray Luminous Galaxy Clusters at Redshift z ~ 0.2: II: CFH12k Weak Lensing Analysis and Global Correlations
• Constraining the population of 6 < z < 10 star-forming galaxies with deep near-IR images of lensing clusters
• The GLARE Survey II. Faint z=6 Ly-alpha Line Emitters in the HUDF
• Searching for the reionization sources
• An Empirically-Calibrated Model For Interpreting the Evolution of Galaxies During the Reionization Era
• Galaxies Under the Cosmic Microscope: Resolved Spectroscopy and New Constraints on the z=1 Tully-Fisher relation

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• A downturn in intergalactic CIV as redshift 6 is approached
• The Highest Resolution Mass Map of Galaxy Cluster Substructure To Date Without Assuming Light Traces Mass: LensPerfect Analysis of Abell 1689
• The UDF05 Follow-up of the HUDF: II. Constraints on Reionization from z-dropout Galaxies
• z~7-10 Galaxies behind Lensing Clusters: Contrast with Field Search Results
• The Effect of Galactic Properties on the Escape Fraction of Ionizing Photons
• Keck spectroscopic survey of strongly lensed galaxies in Abell 1703: further evidence for a relaxed, unimodal cluster
• First direct metallicity measurement of a lensed star-forming galaxy at z=1.7
• First stars and the extragalactic background light: How recent gamma-ray observations constrain the early universe
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