We present ALMA Band~7 observations of a remarkably bright galaxy candidate at zₚₕₒₜ=16.7+1.9-0.3 (MUV=$-21.6$), S5-z17-1, identified in JWST Early Release Observation data of Stephen's Quintet. We do not detect the dust continuum at 866~$μ$m, ruling out the possibility that \ is a low-z dusty starburst with a star-formation rate of 30~M_~yr⁻¹. We detect a 5.1$σ$ 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 [OIII]52$μ$m at $z=16.01$ or [CII]158$μ$m at $z=4.61$, whose line luminosities do not violate the non-detection of the dust continuum in both cases. Together with three other z 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-z solution at z~11--17 is favored in every candidate as a very blue (UV continuum slope of -2.3) and luminous (MUV[-24:$-21]$) system. Still, we find in several candidates that reasonable SED fits ($Δ$ χ²4) are reproduced by type-II quasar and/or quiescent galaxy templates with strong emission lines at z~3--5, where such populations predicted from their luminosity functions and EW([OIII]+H$β$) distributions are abundant in survey volumes used for the identification of the z~11--17 candidates. While these recent ALMA observation results have strengthened the likelihood of the high-z solutions, lower-z possibilities are not completely ruled out in several of the z~11--17 candidates, indicating the need to consider the relative surface densities of the lower-z contaminants in the ultra high-z galaxy search.
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Fujimoto et al. (2022) studied this question.