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Register a new userRELICS-DP7: Spectroscopic Confirmation of a Dichromatic Primeval Galaxy at z ~ 7
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We report the discovery of a spectroscopically-confirmed strong Lyman-$alpha$ emitter at $z=7.0281pm0.0003$, observed as part of the Reionization Cluster Lensing Survey (RELICS). This galaxy, dubbed Dichromatic Primeval Galaxy at $zsim7$ (DP7), shows two distinct components. While fairly unremarkable in terms of its ultraviolet (UV) luminosity ($sim0.3L^{ast}_{UV}$, where $L^{ast}_{UV}$ is the characteristic luminosity), DP7 has one of the highest observed Lyman-$alpha$ equivalent widths (EWs) among Lyman-$alpha$ emitters at $z>6$ ($>200$ Angstrom in the rest frame). The strong Lyman-$alpha$ emission generally suggests a young metal-poor, low-dust galaxy; however, we find that the UV slope $beta$ of the galaxy as a whole is redder than typical star-forming galaxies at these redshifts, $-1.13pm 0.84$, likely indicating, on average, a considerable amount of dust obscuration, or an older stellar population. When we measure $beta$ for the two components separately, however, we find evidence of differing UV colors, suggesting two separate stellar populations. Also, we find that Lyman-$alpha$ is spatially extended and likely larger than the galaxy size, hinting to the possible existence of a Lyman-$alpha$ halo. Rejuvenation or merging events could explain these results. Either scenario requires an extreme stellar population, possibly including a component of Population III stars, or an obscured Active Galactic Nucleus. DP7, with its low UV luminosity and high Lyman-$alpha$ EW, represents the typical galaxies that are thought to be the major contribution to the reionization of the Universe, and for this reason DP7 is an excellent target for follow-up with the James Webb Space Telescope.
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