Redshift Horizon for Detecting the First Galaxies in Far-infrared Surveys

Abstract

We explore the possibility of detecting the first galaxies with the next generation of space-based far-infrared (FIR) telescopes by applying an analytical model of primordial dust emission. Our results indicate that FIR/submillimeter sources at z ⪆ 7 will experience a strong negative K-correction. Systems of a given virial mass would exhibit larger dust luminosities at higher z, as a consequence of the increase in dust temperature driven by the higher temperature floor set by the cosmic microwave background. In addition, high-z systems are more concentrated, which enhances the heating efficiency associated with stellar radiation. By analyzing source densities as a function of z, and considering survey areas of 0.1 and 10 deg2, we find that the redshift horizon for detecting at least one source would be above z ∼ 7 for instrument sensitivities ≲0.1-0.5 and ≲0.5-3.0 μJy, respectively, with the exact values depending on the nature of primordial dust. However, galaxy populations with higher than typical metallicities, star formation efficiencies, and/or dust-to-metal ratios could relax such sensitivity requirements. In addition, the redshift horizon shows a significant dependence on the nature of primordial dust. We conclude that future FIR campaigns could play a crucial role in exploring the nature of dust and star formation in the early universe.