The far-infrared/radio correlation and radio spectral index of galaxies in the SFR–M_∗ plane up to z ∼ 2

Abstract

We study the evolution of the radio spectral index and far-infrared/radio correlation (FRC) across the star-formation rate – stellar masse (i.e. SFR–M_∗) plane up to z ~ 2. We start from a stellar-mass-selected sample of galaxies with reliable SFR and redshift estimates. We then grid the SFR–M_∗ plane in several redshift ranges and measure the infrared luminosity, radio luminosity, radio spectral index, and ultimately the FRC index (i.e. q_(FIR)) of each SFR–M_∗–z bin. The infrared luminosities of our SFR–M_∗–z bins are estimated using their stacked far-infrared flux densities inferred from observations obtained with the Herschel Space Observatory. Their radio luminosities and radio spectral indices (i.e. α, where S_ν ∝ ν^(−α)) are estimated using their stacked 1.4 GHz and 610 MHz flux densities from the Very Large Array and Giant Metre-wave Radio Telescope, respectively. Our far-infrared and radio observations include the most widely studied blank extragalactic fields – GOODS-N, GOODS-S, ECDFS, and COSMOS – covering a total sky area of ~2.0 deg^2. Using this methodology, we constrain the radio spectral index and FRC index of star-forming galaxies with M_∗ > 10^(10) M_⊙ and 0

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