RELICS-DP7: Spectroscopic Confirmation of a Dichromatic Primeval Galaxy at z ~ 7

Abstract

We report the discovery of a spectroscopically-confirmed strong Lyman-$\alpha$ emitter at $z=7.0281\pm 0.0003$, observed as part of the Reionization Cluster Lensing Survey (RELICS). This galaxy, dubbed "Dichromatic Primeval Galaxy" at $z\sim 7$ (DP7), shows two distinct components. While fairly unremarkable in terms of its ultraviolet (UV) luminosity ($\sim 0.3L_{UV}^{\ast }$, where $L_{UV}^{\ast }$ 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, $-1.13\pm 0.84$, 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.

8 pages, 3 figures, 2 table. Accepted for publication in ApJL

References in corpus (15)

• UV Luminosity Functions at redshifts z~4 to z~10: 10000 Galaxies from HST Legacy Fields
• Cosmic Reionization and Early Star-Forming Galaxies: A Joint Analysis of New Constraints from Planck and Hubble Space Telescope
• Using Lyman-alpha to detect galaxies that leak Lyman continuum
• Line Emitting Galaxies Beyond a Redshift of 7: An Improved Method for Estimating the Evolving Neutrality of the Intergalactic Medium
• New observations of z~7 galaxies: evidence for a patchy reionization
• A Spectroscopic Redshift Measurement for a Luminous Lyman Break Galaxy at z=7.730 using Keck/MOSFIRE
• Constraining the neutral fraction of hydrogen in the IGM at redshift 7.5
• Texas Spectroscopic Search for Ly$\alpha$ Emission at the End of Reionization III. the Ly$\alpha$ Equivalent-width Distribution and Ionized Structures at $z>7$
• A Morphological Classification Model to Identify Unresolved PanSTARRS1 Sources: Application in the ZTF Real-Time Pipeline
• ALMA reveals metals yet no dust within multiple components in CR7
• Onset of Cosmic Reionization: Evidence of An Ionized Bubble Merely 680 Myrs after the Big Bang
• Keck Deep Fields. III. Luminosity-dependent Evolution of the Ultraviolet Luminosity and Star Formation Rate Densities at z~4, 3, and 2
• Serendipitous Discovery of an Overdensity of Lyman-Alpha Emitters at z~4.8 in the Cl1604 Supercluster Field
• Spitzer UltRa Faint SUrvey Program (SURFS UP) I: An Overview
• The nature of CR7 revealed with MUSE: a young starburst powering extended Lyman-$\alpha$ emission at z=6.6

Cited by in corpus (6)

• Reionization Era Bright Emission Line Survey: Selection and Characterization of Luminous Interstellar Medium Reservoirs in the z>6.5 Universe
• The discovery of rest-frame UV colour gradients and a diversity of dust morphologies in bright z ~ 7 Lyman-break galaxies
• High Equivalent Width of Hα+[N II] Emission in z~8 Lyman-break Galaxies from IRAC 5.8μm Observations: Evidence for Efficient Lyman-continuum Photon production in the Epoch of Re-ionization
• The ALMA REBELS Survey: Efficient Ly$\alpha$ Transmission of UV-Bright z$\simeq$7 Galaxies from Large Velocity Offsets and Broad Line Widths
• The ALPINE-ALMA [CII] Survey: Investigation of 10 Galaxies at $z\sim 4.5$ with [OII] and [CII] Line Emission $-$ ISM Properties and [OII]$-$SFR Relation
• RELICS: Small Lensed $z\ge 5.5$ Galaxies Selected as Potential Lyman Continuum Leakers