The far-infrared/radio correlation and radio spectral index of galaxies in the SFR–M_∗plane up toz~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 < z < 2.3. We find that α 1.4 GHz 610 MHz does not evolve significantly with redshift or with the distance of a galaxy with respect to the main sequence (MS) of the SFR-M * plane (i.e. Δlog(SSFR) MS = log[SSFR(galaxy)/SSFR MS (M * , z)]). Instead, star-forming galaxies have a radio spectral index consistent with a canonical value of 0.8, which suggests that their radio spectra are dominated by non-thermal optically thin synchrotron emission. We find that the FRC index, q FIR , displays a moderate but statistically significant redshift evolution as q FIR (z) = (2.35±0.08)×(1+z) −0.12 ± 0.04 , consistent with some previous literature. Finally, we find no significant correlation between q FIR and Δlog(SSFR) MS , though a weak positive trend, as observed in one of our redshift bins (i.e. Δ[q FIR ]/Δ[Δlog(SSFR) MS ] = 0.22 ± 0.07 at 0.5 < z < 0.8), cannot be firmly ruled out using our dataset.

The VLA-COSMOS 3 GHz Large Project: Multiwavelength counterparts and the composition of the faint radio population

“…A statistically more robust and detailed analysis , where both the radio and the FIR upper limits are fully taken into account, also finds that the median log (L IR /1.4 GHz) for our sample of star-forming galaxies shows a significant trend with redshift that is qualitatively consistent with what is shown in our Fig. 7 (see also, e.g., Magnelli et al 2015;Calistro Rivera et al 2017). Thus, the choice of a redshift-dependent threshold is fully consistent with the available observational data.…”

CONFIRMING THE EXISTENCE OF A QUIESCENT GALAXY POPULATION OUT TO z = 3: A STACKING ANALYSIS OF MID-, FAR-INFRARED, AND RADIO DATA

“…This includes the assumption about the SED shapes for both the Herschel dust component, as well as the radio spectral slope for the FIR-radio correlation. There may also be systematic differences between the FIR-radio correlation by Bell (2003) used in this work compared to other works in literature (e.g., Ivison et al 2010;Sargent et al 2010;Magnelli et al 2015), with regards to redshift evolution, luminosity evolution, primary sample selection, wavelength sampling of the dust peak and radio emission, etc. It is also unclear if the FIR-radio correlation calibrated for SFGs is applicable to QGs.…”

“Super-deblended” Dust Emission in Galaxies. I. The GOODS-North Catalog and the Cosmic Star Formation Rate Density out to Redshift 6

“…, following Magnelli et al (2015) and Delhaize et al (2017). 28 We find that such a small evolution is also generally warranted by our global SEDs.…”