DRAFT VERSION OCTOBER 5, 2021 Typeset using L A T E X twocolumn style in AASTeX63 RELICS-DP7: Spectroscopic Confirmation of a Dichromatic Primeval Galaxy at z ∼ 7 DEBORA PELLICCIA , 1, 2 VICTORIA STRAIT , 2 BRIAN C. LEMAUX , 2 MARU ˇ SA BRADA ˇ C , 2 DAN COE , 3 PATRICIA BOLAN , 2 LARRY D. BRADLEY , 3 BRENDA FRYE , 4 PRATIK GANDHI , 2 RAMESH MAINALI , 5 CHARLOTTE MASON , 6, 7 MASAMI OUCHI , 8, 9 KEREN SHARON , 10 MICHELE TRENTI , 11, 12 AND ADI ZITRIN 13 1 UCO/Lick Observatory, Department of Astronomy & Astrophysics, UC Santa Cruz, 1156 High Street, Santa Cruz, CA, 95064, USA 2 Department of Physics & Astronomy, University of California, Davis, One Shields Ave, Davis, CA 95616, USA 3 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA 4 Department of Astronomy, Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ, 85721, USA 5 Observational Cosmology Lab, NASA Goddard Space Flight Center, 8800 Greenbelt Rd.,Greenbelt, MD 20771, USA 6 Harvard-Smithsonian Center for Astrophysics, 60 Garden St, Cambridge, MA, 02138, USA 7 Hubble Fellow 8 Institute for Cosmic Ray Research, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8582, Japan 9 Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI), University of Tokyo, Kashiwa, Chiba 277-8583, Japan 10 Department of Astronomy, University of Michigan, 1085 S. University Ave, Ann Arbor, MI 48109, USA 11 School of Physics, University of Melbourne, VIC 3010, Australia 12 ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), VIC 2010, Australia 13 Department of Physics, Ben-Gurion University, Beer-Sheva 84105, Israel (Received; Revised; Accepted) Submitted to ApJL ABSTRACT We report the discovery of a spectroscopically-confirmed strong Lyman-α emitter at z =7.0281 ± 0.0003, observed as part of the Reionization Cluster Lensing Survey (RELICS). This galaxy, dubbed “Dichromatic Primeval Galaxy” at z ∼ 7 (DP7), shows two distinct components. While fairly unremarkable in terms of its ultraviolet (UV) luminosity (∼ 0.3L ∗ UV , where L ∗ UV is the characteristic luminosity), DP7 has one of the high- est observed Lyman-α equivalent widths (EWs) among Lyman-α emitters at z> 6 (> 200 ˚ A in the rest frame). The strong Lyman-α emission generally suggests a young metal-poor, low-dust galaxy; however, we find that the UV slope β of the galaxy as a whole is quite red, -1.13 ± 0.84, likely indicating, on average, a consider- able amount of dust obscuration, or an older stellar population. When we measure β for the two components separately, however, we find evidence of differing UV colors, suggesting two separate stellar populations. Also, we find that Lyman-α is spatially extended and likely larger than the galaxy size, hinting to the possible exis- tence of a Lyman-α 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-α 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. Keywords: Galaxies, High-redshift galaxies, Galaxy evolution, Reionization 1. INTRODUCTION Spectroscopic observations of distant galaxies (z> 6) al- low us to constrain early galaxy formation and the epoch of dpelliccia@ucolick.org vbstrait@ucdavis.edu reionization. In particular, the λ1215.7 ˚ A Lyman-α line is both the strongest recombination line of hydrogen intrinsi- cally and resonantly scattered by neutral hydrogen, making its strength a sensitive gauge of the amount of neutral hydro- gen in this epoch. The study of Lyman-α emission in galaxies is commonly used to constrain the neutral fraction of the In- terGalactic Medium (IGM) and, hence, different reionization timelines (e.g., Robertson et al. 2015; Mason et al. 2019). Identifying ionized and neutral regions of the IGM not only arXiv:2011.08857v1 [astro-ph.GA] 17 Nov 2020