Evolution of dust temperature of galaxies through cosmic time as seen by Herschel

We study the dust properties of galaxies in the redshift range 0.1 ≲ z ≲ 2.8 observed by the Herschel Space Observatory in the field of the Great Observatories Origins Deep Survey-North as part of the PACS Extragalactic Probe (PEP) and Herschel Multi-tiered Extragalactic Survey (HerMES) key programmes. Infrared (IR) luminosity (L_(IR)) and dust temperature (T_dust) of galaxies are derived from the spectral energy distribution fit of the far-IR (FIR) flux densities obtained with the PACS and SPIRE instruments onboard Herschel. As a reference sample, we also obtain IR luminosities and dust temperatures of local galaxies at z < 0.1 using AKARI and IRAS data in the field of the Sloan Digital Sky Survey. We compare the L_(IR)–T_dust relation between the two samples and find that the median Tdust of Herschel-selected galaxies at z ≳ 0.5 with L_(IR) ≳ 5 × 10^(10) L_⊙ appears to be 2–5 K colder than that of AKARI-selected local galaxies with similar luminosities, and the dispersion in T_dust for high-z galaxies increases with L_(IR) due to the existence of cold galaxies that are not seen among local galaxies. We show that this large dispersion of the L_(IR)−T_dust relation can bridge the gap between local star-forming galaxies and high-z submillimetre galaxies (SMGs). We also find that three SMGs with very low T_dust (≲20 K) covered in this study have close neighbouring sources with similar 24-μm brightness, which could lead to an overestimation of FIR/(sub)millimetre fluxes of the SMGs.