Spitzer Space Telescope Constraint on the Stellar Mass of a z = 6.96 Lyman Alpha Emitter

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We obtained mid-infrared 3.6 and 4.5 micron imaging of a z=6.96 Lyman alpha emitter (LAE) IOK-1 discovered in the Subaru Deep Field, using Spitzer Space Telescope Infrared Array Camera observations. After removal of a nearby bright source, we find that IOK-1 is not significantly detected in any of these infrared bands to m₃.6 24.00 and m₄.5 23.54 at 3 sigma. Fitting population synthesis models to the spectral energy distribution consisting of the upper limit fluxes of the optical to infrared non-detection images and fluxes in detection images, we constrain the stellar mass M* of IOK-1. This LAE could have either a mass as low as M* < 2-9 x 10⁸ Msun for the young age (< 10 Myr) and the low dust reddening (Aᵥ 0) or a mass as large as M* < 1-4 x 10¹⁰ Msun for either the old age (> 100 Myr) or the high dust reddening (Aᵥ 1.5). This would be within the range of masses of z 3-6.6 LAEs studied to date, 10⁶-10¹⁰ Msun. Hence, IOK-1 is not a particularly unique galaxy with extremely high mass or low mass but is similar to one of the LAEs seen at the later epochs.