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Astrophysical Journal


We have carried out a search for galaxies at z ∼ 7–10 in ∼14.4 arcmin2 of new NICMOS parallel imaging taken in the Great Observatories Origins Deep Survey (5.9 arcmin2), the Cosmic Origins Survey (7.2 arcmin2), and SSA22 (1.3 arcmin2). These images reach 5σ sensitivities of J110 = 26.0–27.5 (AB), and combined they increase the amount of deep near-infrared data by more than 60% in fields where the investment in deep optical data has already been made. We find no z > 7 candidates in our survey area, consistent with the Bouwens et al. measurements at z ∼ 7 and 9 (over 23 arcmin2), which predict 0.7 galaxies at z ∼ 7 and <0.03 galaxies at z ∼ 9. We estimate that 10%–20% of z > 7 galaxies are missed by this survey, due to incompleteness from foreground contamination by faint sources. For the case of luminosity evolution, assuming a Schecter parameterization with a typical ϕ* = 10−3 Mpc−3, we find M*> − 20.0 for z ∼ 7 and M*> − 20.7 for z ∼ 9 (68% confidence). This suggests that the downward luminosity evolution of Lyman break galaxies continues to z ∼ 7, although our result is marginally consistent with the z ∼ 6 luminosity function of Bouwens et al. In addition, we present newly acquired deep MMT/Megacam imaging of the z ∼ 9 candidate JD2325+1433, first presented in Henry et al. The resulting weak but significant detection at i' indicates that this galaxy is most likely an interloper at z ∼ 2.7.