Physics and Astronomy
We identify four unusually bright (H160,AB < 25.5) galaxies from Hubble Space Telescope (HST) and Spitzer CANDELS data with probable redshifts z ∼ 7–9. These identifications include the brightest-known galaxies to date at z 7.5. As Y-band observations are not available over the full CANDELS program to perform a standard Lyman-break selection of z > 7 galaxies, we employ an alternate strategy using deep Spitzer/IRAC data. We identify z ∼ 7.1–9.1 galaxies by selecting z 6 galaxies from the HST CANDELS data that show quite red IRAC [3.6]−[4.5] colors, indicating strong [O III]+Hβ lines in the 4.5 μm band. This selection strategy was validated using a modest sample for which we have deep Y-band coverage, and subsequently used to select the brightest z 7 sources. Applying the IRAC criteria to all HST-selected optical dropout galaxies over the full ∼900 arcmin2 of the CANDELS survey revealed four unusually bright z ∼ 7.1, 7.6, 7.9, and 8.6 candidates. The median [3.6]−[4.5] color of our selected z ∼ 7.1–9.1 sample is consistent with rest-frame [O III]+Hβ EWs of ∼1500 Å in the [4.5] band. Keck/MOSFIRE spectroscopy has been independently reported for two of our selected sources, showing Lyα at redshifts of 7.7302 ± 0.0006 and - + 8.683 0.004 0.001, respectively. We present similar Keck/MOSFIRE spectroscopy for a third selected galaxy with a probable 4.7σ Lyα line at zspec = 7.4770 ± 0.0008. All three have H160-band magnitudes of ∼25 mag and are ∼0.5 mag more luminous (M1600 ∼ −22.0) than any previously discovered z ∼ 8 galaxy, with important implications for the UV luminosity function (LF). Our three brightest and highest redshift z > 7 galaxies all lie within the CANDELS-EGS field, providing a dramatic illustration of the potential impact of field-to-field variance
Original Publication Information
Roberts-Borsani, G. W., et al. "z Galaxies with Red Spitzer/IRAC [3.6]–[4.5] Colors in the Full CANDELS Data Set: The Brightest-Known Galaxies at z ~ 7-9 and a Probable Spectroscopic Confirmation at z = 7.48." 2016. The Astrophysical Journal 823(2): 17 pp.
Roberts-Borsani, G. W.; Bouwens, R. J.; Oesch, P. A.; Labbe, I.; Smit, R.; Illingworth, G. D.; van Dokkum, P. G.; Holden, B.; Gonzalez, V.; Stefanon, M.; Holwerda, Benne W.; and Wilkins, S. M., "z 7 galaxies with red Spitzer/IRAC [3.6]–[4.5] colors in the full CANDELS data set : the brightest-known galaxies AT z ∼ 7–9 and a probable spectroscopic confirmation at z = 7.48." (2016). Faculty Scholarship. 165.