Deep uGMRT observations of the ELAIS-North 1 field: statistical properties of radio-infrared relations up to z ∼2

Abstract

Comprehending the radio-infrared (IR) relations of the faint extragalactic radio sources is important for using radio emission as a tracer of star formation in high redshift ( z) star-forming galaxies (SFGs). Using deep uGMRT observations of the ELAIS-N1 field in the 0.3-0.5 GHz range, we study the statistical properties of the radio-IR relations and the variation of the ' q -parameter' up to z = 2 after broadly classifying the faint sources as SFGs and AGN. We find the dust temperature ( T dust ) to increase with z. This gives rise to q 24 μm , measured at 24 μm, to increase with z as the peak of IR emission shifts towards shorter wavelengths, resulting in the largest scatter among different measures of q -parameters. q 70 μm measured at 70 μm, and q TIR using total-IR (TIR) emission are largely unaffected by T dust . We observe strong, non-linear correlations between the radio luminosities at 0.4 and 1.4 GHz with 70 μm luminosity and TIR luminosity( L TIR ). To assess the possible role of the radio-continuum spectrum in making the relations non-linear, for the first time we study them at high z using integrated radio luminosity ( L RC ) in the range 0.1-2 GHz. In SFGs, the L RC -L TIR relation remains non-linear with a slope of 1.07 ±0.02, has a factor of 2 lower scatter compared to monochromatic radio luminosities, and q RC TIR decreases with z as q RC TIR = (2 . 27 ±0 . 03) (1 + z) -0 . 12 ±0 . 03 . A redshift variation of q is a natural consequence of non-linearity. We suggest that a redshift evolution of magnetic field strengths and/or cosmic ray acceleration efficiency in high- z SFGs could give rise to non-linear radio-IR relations. © 2022 The Author(s).