  We present ALMA Band~7 observations of a remarkably bright galaxy candidate
at $z_{\rm phot}$=$16.7^{+1.9}_{-0.3}$ ($M_{\rm UV}$=$-21.6$), S5-z17-1,
identified in JWST Early Release Observation data of Stephen's Quintet. We do
not detect the dust continuum at 866~$\mu$m, ruling out the possibility that
\targb\ is a low-$z$ dusty starburst with a star-formation rate of $\gtrsim
30$~$M_{\odot}$~yr$^{-1}$. We detect a 5.1$\sigma$ line feature at
$338.726\pm0.007$~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$\mu$m at $z=16.01$ or [CII]158$\mu$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 $z\gtrsim$ 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\sim$11--17 is favored in every candidate as a very blue (UV continuum slope
of $\simeq-2.3$) and luminous ($M_{\rm UV}\simeq[-$24:$-21]$) system. Still, we
find in several candidates that reasonable SED fits ($\Delta$
$\chi^{2}\lesssim4$) are reproduced by type-II quasar and/or quiescent galaxy
templates with strong emission lines at $z\sim3$--5, where such populations
predicted from their luminosity functions and EW([OIII]+H$\beta$) distributions
are abundant in survey volumes used for the identification of the $z\sim$11--17
candidates. While these recent ALMA observation results have strengthened the
likelihood of the high-$z$ solutions, lower-$z$ possibilities are not
completely ruled out in several of the $z\sim$11--17 candidates, indicating the
need to consider the relative surface densities of the lower-$z$ contaminants
in the ultra high-$z$ galaxy search.

Astrophysics of Galaxies;Cosmology and Nongalactic Astrophysics