Stellar Populations of Lyman Alpha Emitters at z~6-7: Constraints on the Escape Fraction of Ionizing Photons from Galaxy Building Blocks

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We investigate the stellar populations of Lyman alpha emitters (LAEs) at z=5.7 and 6.6 in a 0.65 deg^2 sky of the Subaru/XMM-Newton Deep Survey (SXDS) Field, using deep images taken with Subaru/Suprime-Cam, UKIRT/WFCAM, and Spitzer/IRAC.

• We produce stacked multiband images at each redshift from 165 (z=5.7) and 91 (z=6.6) IRAC-undetected objects, to derive typical spectral energy distributions (SEDs) of z~6-7 LAEs for the first time.
• The stacked LAEs have as blue UV continua as the HST/WFC3 z-dropout galaxies of similar Muv, with a spectral slope beta ~ -3, but at the same time they have red UV-to-optical colors with detection in the 3.6um band.
• Using SED fitting we find that the stacked LAEs have low stellar masses of ~(3-10)*10^7 Msun, very young ages of ~1-3 Myr, negligible dust extinction, and strong nebular emission from the ionized interstellar medium, although the z=6.6 object is fitted similarly well with high-mass models without nebular emission; inclusion of nebular emission reproduces the red UV-to-optical color while keeping the UV color sufficiently blue.