Signatures of first galaxies at FIR/sub-mm wavelengths

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 $z$.