jats:titleAbstract</jats:title> jats:pWe present Atacama Large Millimeter/submillimeter Array (ALMA) Band 7 observations of a remarkably bright galaxy candidate at jats:inline-formula jats:tex-math

</jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> mml:msub mml:mrow mml:miz</mml:mi> </mml:mrow> mml:mrow mml:miphot</mml:mi> </mml:mrow> </mml:msub> mml:mo=</mml:mo> mml:msubsup mml:mrow mml:mn16.7</mml:mn> </mml:mrow> mml:mrow mml:mo−</mml:mo> mml:mn0.3</mml:mn> </mml:mrow> mml:mrow mml:mo+</mml:mo> mml:mn1.9</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaceb67ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> (jats:italicM</jats:italic> jats:subUV</jats:sub> = −21.6), S5-z17-1, identified in James Webb Space Telescope (JWST) Early Release Observation data of Stephen’s Quintet. We do not detect the dust continuum at 866 jats:italicμ</jats:italic>m, ruling out the possibility that S5-z17-1 is a low-jats:italicz</jats:italic> dusty starburst with a star formation rate of ≳30 jats:italicM</jats:italic> jats:sub⊙</jats:sub> yrjats:sup−1</jats:sup>. We detect a 5.1jats:italicσ</jats:italic> line feature at 338.726 ± 0.007 GHz exactly coinciding with the JWST source position, with a 2% likelihood of the signal being spurious. The most likely line identification would be [O jats:sciii</jats:sc>]52 jats:italicμ</jats:italic>m at jats:italicz</jats:italic> = 16.01 or [C jats:scii</jats:sc>]158 jats:italicμ</jats:italic>m at jats:italicz</jats:italic> = 4.61, whose line luminosities do not violate the nondetection of the dust continuum in both cases. Together with three other jats:italicz</jats:italic> ≳ 11–13 candidate galaxies recently observed with ALMA, we conduct a joint ALMA and JWST spectral energy distribution (SED) analysis and find that the high-jats:italicz</jats:italic> solution at jats:italicz</jats:italic> ∼ 11–17 is favored in every candidate as a very blue (UV continuum slope of ≃−2.3) and luminous (jats:italicM</jats:italic> jats:subUV</jats:sub> ≃ [ − 24:−21]) system. Still, we find in several candidates that reasonable SED fits (Δjats:italicχ</jats:italic> jats:sup2</jats:sup> ≲ 4) are reproduced by type II quasar and/or quiescent galaxy templates with strong emission lines at jats:italicz</jats:italic> ∼ 3–5, where such populations predicted from their luminosity functions and EW([O jats:sciii</jats:sc>]+Hjats:italicβ</jats:italic>) distributions are abundant in survey volumes used for the identification of the jats:italicz</jats:italic> ∼ 11–17 candidates. While these recent ALMA observation results have strengthened the likelihood of the high-jats:italicz</jats:italic> solutions, lower-jats:italicz</jats:italic> possibilities are not completely ruled out in several of the jats:italicz</jats:italic> ∼ 11–17 candidates, indicating the need to consider the relative surface densities of the lower-jats:italicz</jats:italic> contaminants in the ultra-high-jats:italicz</jats:italic> galaxy search.</jats:p>