Euclid Quick Data Release (Q1): XXIII. The average far-infrared properties of Euclid-selected star-forming galaxies

The first Euclid Quick Data Release (Q1) contains millions of galaxies with excellent optical and near-infrared (IR) coverage. To complement this dataset, we investigate the average far-IR properties of Euclid-selected main sequence (MS) galaxies using existing Herschel and SCUBA-2 data. We used 17.6 deg2 (2.4 deg2) of overlapping Herschel (SCUBA-2) data, containing 2.6 million (240 000) MS galaxies. We binned the Euclid catalogue by stellar mass and photometric redshift and performed a stacking analysis following SimStack, which accounts for galaxy clustering and bin-to-bin correlations. We detected stacked far-IR flux densities across a significant fraction of the bins. We fitted modified blackbody spectral energy distributions in each bin and derived mean dust temperatures (Td), dust masses (Md), and star-formation rates (SFRs). We find similar mean SFRs compared to the Euclid catalogue, and we show that the average dust-to-stellar mass ratios decreased from z  ≃  1 to the present day. Average dust temperatures are largely independent of stellar mass and are well-described by the function T2  +  (T1  −  T2) e−t/τ, where t is the age of the Universe, T1  =  (79.7 ± 7.4) K, T2  =  (23.2 ± 0.1) K, and τ  =  (1.6 ± 0.1) Gyr. We argue that since the dust temperatures converge to a non-zero value below z  =  1, the dust is now primarily heated by the existing cooler and older stellar population, as opposed to hot young stars in star-forming regions at higher redshifts. We show that since the dust temperatures are independent of stellar mass, the correlation between dust temperature and SFR depends on stellar mass. Lastly, we estimate the contribution of the Euclid catalogue to the cosmic IR background (CIB), finding that it accounts for > 60% of the CIB at 250, 350, and 500 μm. As the Euclid mission progresses, larger catalogues will allow us to probe the far-IR properties of MS galaxies out to higher redshifts and lower stellar masses, potentially recovering the complete CIB.