2020ApJ...900...68C

This paper presents a new approach to deriving far-infrared (FIR) photometric redshifts for galaxies based on their reprocessed emission from dust at rest-frame FIR through millimeter wavelengths. FIR photometric redshifts ("FIR-z") have been used over the past decade to derive redshift constraints for highly obscured galaxies that lack photometry at other wavelengths like the optical/near-IR. Most literature FIR-z fits are performed through χ² minimization to a single galaxy's FIR template spectral energy distribution (SED). The use of a single galaxy template, or modest set of templates, can lead to an artificially low uncertainty estimate on FIR-z's because real galaxies display a wide range in intrinsic dust SEDs. I use the observed distribution of galaxy SEDs (for well-constrained samples across 0< z< 5) to motivate a new FIR through millimeter photometric redshift technique called MMPZ. The MMPZ algorithm asserts that galaxies are most likely drawn from the empirically observed relationship between rest-frame peak wavelength, λ_peak, and total IR luminosity, L_IR; the derived photometric redshift accounts for the measurement uncertainties and intrinsic variation in SEDs at the inferred L_IR, as well as heating from the cosmic microwave background at z≳5. The MMPZ algorithm has a precision of σ_Δz/(1+z)_~0.3–0.4, similar to single-template fits, while providing a more accurate estimate of the FIR-z uncertainty with reduced chi-squared of order O (χ_ν²)=1, compared to alternative FIR photometric redshift techniques (with O (χ_ν²)~10–10³).