Deep Submillimeter and Radio Observations of the SSA22 Field. IV. Spectral Energy Distributions, Star Formation Histories, and the Infrared–Radio Correlation of the 850 μm–selected Submillimeter Galaxies

Abstract

We analyze the spectral energy distributions (SEDs), star formation histories, and infrared–radio correlation (IRRC) of 221 850 μm–selected submillimeter galaxies (SMGs) in the SSA22 deep field, including both field and protocluster SMGs. The average SED reveals that SMGs have cooler dust temperatures than local ULIRGs or starburst systems, and that higher-redshift SMGs tend to be more luminous and exhibit warmer dust. The median mass-weighted age is 0.57 ± 0.21 Gyr. Most galaxies in our sample began forming ∼1.68 ± 0.07 Gyr after the Big Bang, entered the “SMG phase” after ∼1 Gyr of evolution—when they are predominantly observed—and largely transitioned out of the SMG phase to become quiescent within an additional ∼0.2 Gyr. A subset of massive galaxies shows rapid early assembly with high star formation efficiencies (ϵ ∼ 0.2–0.8). The majority of SMGs reside at the high-mass end of the star-forming main sequence, with a characteristic stellar mass of Mstar ∼ 1011 M⊙, above which galaxies are predominantly either on the main sequence or already quenched. We observe a downsizing trend: more massive galaxies tend to “mature” earlier, completing their major episodes of star formation at higher redshifts compared to lower-mass systems. Our sample contributes ∼29% ± 6% (21% ± 3%) to the cosmic star formation rate density (stellar mass density). The median IRRC parameter qIR is 2.37 ± 0.04, evolving as (1 + z)−0.11 ± 0.04, likely due to active galactic nucleus contributions at high redshift and intrinsic differences between low- and high-redshift populations.