  We explore the possibility of detecting first galaxies with a generic
far-infrared/sub-millimeter telescope by applying an analytical model of
primordial dust emission. As shown in previous works, galaxies at redshifts
$z>7$ experience a strong negative K-correction in such a way that systems of
similar masses are brighter at higher $z$. In addition, at a given mass and
$z$, our model predicts that luminosity fluxes increase proportionally to the
dust-to-metal ratios ($D/M$) of primeval sources. We evaluate the observability
of model sources at different $z>7$ as a function of the observed survey area
($\Delta \Omega$) and sensitivity ($S$) of a generic instrument. Assuming
$\Delta \Omega \sim 10~{\rm deg}^2$ and a plausible $S \sim 1~{\mu}{\rm Jy}$
for a near future survey, we could assure the detection of at least one typical
source with $D/M \sim 5\times10^{-3}$ at $z>7$. For $S\gtrsim 1~{\mu}{\rm Jy}$
and $\Delta \Omega \lesssim 10~{\rm deg}^2$, higher than typical $D/M$ are
required to detect at least one individual source at $z>7$. The observability
of model galaxies is also affected by the size distribution of dust grains,
specially towards higher $z$.
