Abstract

We study the stellar population properties of the IRAC-detected 6 less than or similar to z less than or similar to 10 galaxy candidates from the Spitzer UltRa Faint SUrvey Program. Using the Lyman Break selection technique, we find a total of 17 galaxy candidates at 6 less than or similar to z less than or similar to 10 from Hubble Space Telescope images (including the full-depth images from the Hubble Frontier Fields program for MACS 1149 and MACS 0717) that have detections at signal-to-noise ratios >= 3 in at least one of the IRAC 3.6 and 4.5 mu m channels. According to the best mass models available for the surveyed galaxy clusters, these IRAC-detected galaxy candidates are magnified by factors of similar to 1.2-5.5. Due to the magnification of the foreground galaxy clusters, the rest-frame UV absolute magnitudes M-1600 are between -21.2 and -18.9 mag, while their intrinsic stellar masses are between 2 x 10(8)M(circle dot) and 2.9 x 10(9)M(circle dot). We identify two Ly alpha emitters in our sample from the Keck DEIMOS spectra, one at z(Ly alpha) = 6.76 (in RXJ 1347) and one at z(Ly alpha) = 6.32 (in MACS 0454). We find that 4 out of 17 z greater than or similar to 6 galaxy candidates are favored by z less than or similar to 1 solutions when IRAC fluxes are included in photometric redshift fitting. We also show that IRAC [3.6]-[4.5] color, when combined with photometric redshift, can be used to identify galaxies which likely have strong nebular emission lines or obscured active galactic nucleus contributions within certain redshift windows.