RELICS: Properties of z ≥ 5.5 Galaxies Inferred from Spitzer and Hubble Imaging, Including A Candidate z ∼ 6.8 Strong [O iii] emitter

We present constraints on the physical properties (including stellar mass, age, and star formation rate) of 207 6 less than or similar to z less than or similar to 8 galaxy candidates from the Reionization Lensing Cluster Survey (RELICS) and Spitzer-RELICS surveys. We measure photometry using T-PHOT and perform spectral energy distribution fitting using EAzY and BAGPIPES. Of the 207 candidates for which we could successfully measure (or place limits on) Spitzer fluxes, 23 were demoted to likely z < 4. Among the high-z candidates, we find intrinsic stellar masses between 1 x 10(6)MM= 6.5 galaxies with detections in Spitzer/IRAC imaging, several of which show evidence for some combination of evolved stellar populations, large contributions of nebular emission lines, and/or dust. Among these is PLCKG287+32-2013, one of the brightest z similar to 7 candidates known (AB mag 24.9 at 1.6 mu m) with a Spitzer 3.6 mu m flux excess suggesting strong [O iii] + H-beta emission (similar to 1000 A rest-frame equivalent width). We discuss the possible uses and limits of our sample and present a public catalog of Hubble + Spitzer photometry along with physical property estimates for all objects in the sample. Because of their apparent brightnesses, high redshifts, and variety of stellar populations, these objects are excellent targets for follow-up with the James Webb Space Telescope.

Automated summary

The study presents constraints on the physical properties of 207 galaxy candidates with redshifts between 6 < z < 8, including evidence of evolved stellar populations, nebular emission lines, and dust. Among these candidates, PLCKG287+32-2013 stands out as one of the brightest known z ~ 7 candidates with strong [O iii] + H-beta emission.