A JWST Pa <i>α</i> Calibration of the Radio Luminosity–Star Formation Rate Relation at <i>z</i> ∼ 1.3

Abstract As radio emission from normal galaxies is a dust-free tracer of star formation, tracing the star formation history of the Universe is a key goal of the Square Kilometre Array and the Next-Generation Very Large Array. In order to investigate how well radio luminosity traces star formation rate (SFR) in the early Universe, we have examined the radio properties of a JWST Pa α sample of galaxies at 1.0 ≲ z ≲ 1.8. In the GOODS-S field, we cross-matched a sample of 506 FRESCO Pa α emitters with the 1.23 GHz radio continuum data from the MeerKAT MIGHTEE survey, finding 47 detections. After filtering for active galactic nuclei (via X-ray detections, hot mid-infrared dust, and extended radio emission), as well as blended sources, we obtained a sample of star-forming galaxies comprising 11 cataloged radio detections, 18 noncataloged detections (at ≈3 σ –5 σ ), and 298 undetected sources. Stacking the 298 undetected sources, we obtain a 3.3 σ detection in the radio. This sample, along with a local sample of Pa α emitters, lies along previous radio luminosity/SFR relations from local (&lt;0.2) to high redshift ( z ∼ 1). Fitting the FRESCO data at 1.0 ≲ z ≲ 1.8, we find <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>1</mml:mn> <mml:mo>.</mml:mo> <mml:mi mathvariant="normal">4GHz</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mspace width="0.25em"/> <mml:mo>=</mml:mo> </mml:math> (1.31 ± 0.17) × <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mspace width="0.25em"/> <mml:mi>log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">SFR</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">Pa</mml:mi> <mml:mi>α</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mspace width="0.25em"/> <mml:mo>+</mml:mo> </mml:math> (21.36 ± 0.17), which is consistent with other literature relations. We can explain some of the observed scatter in the L 1.4GHz /SFR Pa α correlation by a toy model in which the synchrotron emission is a delayed/averaged tracer of the instantaneous Pa α SFR by ∼10/75 Myr.