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

Abstract

z 7 galazies 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 atz= 7.48Article (Published Version) http://sro.sussex.ac.uk Roberts-Borsani, G W, Bouwens, R J, Oesch, P A, Labbe, I, Smit, R, Illingworth, G D, van Dokkum, P, Holden, B, Gonzalez, V, Stefanon, M, Holwerda, B and Wilkins, S (2016) z 7 ≳ galazies with red spitzer/IRAC [3.6]-[4.5] colors in the full CANDELS data set: the brightestknown galaxies at z 7-9 and a probable spectroscopic confirmation atz= 7.48. Astrophysical Copyright and reuse:Sussex Research Online is a digital repository of the research output of the University.Copyright and all moral rights to the version of the paper presented here belong to the individual author(s) and/or other copyright owners. To the extent reasonable and practicable, the material made available in SRO has been checked for eligibility before being made available.Copies of full text items generally can be reproduced, displayed or performed and given to third parties in any format or medium for personal research or study, educational, or not-for-profit purposes without prior permission or charge, provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way. < 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 arcmin 2 of the CANDELS survey revealed four unusually bright z ∼ 7.1, 7.6, 7.9, and 8.6 candidates. The median 0.001 , respectively. We present similar Keck/MOSFIRE spectroscopy for a third selected galaxy with a probable 4.7σ Lyα line at z spec = 7.4770 ± 0.0008. All three have H 160 -band magnitudes of ∼25 mag and are ∼0.5 mag more luminous (M 1600 ∼ −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.

HST Imaging of the Brightest z ∼ 8–9 Galaxies from UltraVISTA: The Extreme Bright End of the UV Luminosity Function

“…Indeed, spectroscopic confirmation has recently been obtained for three UV-luminous (M 22 UV~-mag) galaxies at z 7.5 8.7 -with H 25.1 AB selected from CANDELS fields (Roberts-Borsani et al 2016), one at z 8.7 (Zitrin et al 2015) and one at z 11 (GN-z11; Oesch et al 2016). Furthermore, the lower spatial resolution of ground-based observations, compared to HST data, can blend the signal from mergers or from physically unrelated objects and hence make them appear as single sources (e.g., Bowler et al 2017), resulting in an over-estimate of the bright end of the LF and an underestimate of the LF at lower luminosities.…”

“…Distribution with redshift of the absolute magnitude of the bright LBGs detected so far at z 7  . We include measurements of Oesch et al (2014), Bouwens et al (2015), Roberts-Borsani et al (2016), Calvi et al (2016), Bowler et al (2017), and Ono et al (2017) as indicated by the legend. Our candidate LBGs are marked as red points with error bars and lie at the high-luminosity end of all candidate z 8 LBGs to date.…”

Optical Line Emission from z ∼ 6.8 Sources with Deep Constraints on Lyα Visibility

“…An intriguing possibility is that different physical properties of the H II regions concur in explaining both Lyα visibility and a larger EW([O III]+Hβ) (see also Roberts-Borsani et al 2016;Stark et al 2017). The IRAC color of the Lyα emitting galaxies can thus be explained by these objects being younger and more metal-poor, and thus with harder ionization fields, than nonemitting ones.…”

“…The spectral energy distribution of objects in the reionization epoch is affected by emission from [O III] 4959,5007 ll and Hβ at IR wavelengths, resulting in a bluing of the IRAC 3.6-4.5 μm color at z∼6.6-6.9, where the lines affect the 3.6 μm band, and a reddening at z>7 when they enter the 4.5 μm one (Wilkins et al 2013). These signatures yielded evidence of extremely strong line emission in high-z galaxies, and enabled more accurate photometric redshifts and constraints on their specific star formation rate (SSFR; Finkelstein et al 2013;Smit et al 2014Smit et al , 2015Zitrin et al 2015;Roberts-Borsani et al 2016).…”

A Multiply-Imaged z ∼ 6.3 Lyman Alpha Emitter candidate behind Abell 2261

“…Since we know (in part from SED models) which lines are typically stronger in star-forming young galaxies, we can anticipate the effect of brightening on the broadband photometry at a given redshift. This selection technique is similar in nature to that recently adopted by Smit et al (2014Smit et al ( , 2015 and Roberts-Borsani et al (2016) to successfully search for z ∼ 6 − 8 galaxies with strong rest-frame optical emission lines. For example, all 4 objects at z > 7 predicted by Roberts-Borsani et al (2016) to be prominent emission line galaxies from their unusual broadband colors were later found to exhibit Lyα in follow-up observations (Oesch et al 2015;Stark et al 2015;Zitrin et al 2015c;Roberts-Borsani et al 2016).…”