SERENADE. II. An ALMA Multiband Dust Continuum Analysis of 28 Galaxies at 5 < z < 8 and the Physical Origin of the Dust Temperature Evolution

Abstract

We present an analysis of the Atacama Large Millimeter-submillimeter Array (ALMA) multiband dust continuum observations for 28 spectroscopically confirmed bright Lyman break galaxies at 5 < z < 8. Our sample consists of 11 galaxies at z ∼ 6 newly observed in our ALMA program, which substantially increases the number of 5 < z < 8 galaxies with both rest-frame 88 and 158 μm continuum observations, allowing us to simultaneously measure the IR luminosity and dust temperature for a statistical sample of z ≳ 5 galaxies for the first time. We derive the relationship between the ultraviolet (UV) slope (βUV) and infrared excess (IRX) for the z ∼ 6 galaxies, and find a shallower IRX–βUV relation compared to the previous results at z ∼ 2–4. Based on the IRX–βUV relation consistent with our results and the βUV–MUV relation including fainter galaxies in the literature, we find a limited contribution of the dust-obscured star formation to the total star formation rate density, ∼30% at z ∼ 6. Our measurements of the dust temperature at z ∼ 6–7, on average, support a gentle increase of Tdust from z = 0 to z ∼ 6–7. Using an analytic model with parameters consistent with recent James Webb Space Telescope results, we discuss that the observed redshift evolution of the dust temperature can be reproduced by an ∼0.6 dex decrease in the gas depletion timescale and ∼0.4 dex decrease in the metallicity. The variety of Tdust observed at high redshifts can also be naturally explained by scatters around the star formation main sequence and average mass–metallicity relation including an extremely high dust temperature of Tdust > 80 K observed in a galaxy at z = 8.3.