Expanding the search for galaxies at z ∼ 7-10 with new nicmos parallel fields

Abstract

We have carried out a search for galaxies at z 7-10 in 14.4arcmin 2 of new NICMOS parallel imaging taken in the Great Observatories Origins Deep Survey (5.9arcmin2), the Cosmic Origins Survey (7.2arcmin2), and SSA22 (1.3arcmin2). These images reach 5σ sensitivities of J 110 = 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 23arcmin2), 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. © 2009. The American Astronomical Society. All rights reserved.