PEARLS: JWST Counterparts of Micro-Jy Radio Sources in the NEP Time Domain Field. II. All Four Spokes

TL;DR

This study uses JWST/NIRCam data to identify and analyze the properties of radio source counterparts in the NEP TDF, revealing insights into their redshift, star formation, and AGN activity.

Contribution

First comprehensive analysis of JWST counterparts to micro-Jy radio sources in the NEP TDF, highlighting AGN presence and star formation characteristics.

Findings

206 out of 211 radio sources have counterparts at 4.4 microns.

Median redshift of host galaxies is 1.14.

Approximately 79% of radio emission is from star formation, 21% possibly from AGN or dust-obscured star formation.

Abstract

JWST/NIRCam observations in the North Ecliptic Pole Time Domain Field (TDF) identify 4.4 micron counterparts for 206 of 211 radio sources with S(3 GHz) \gapprox 5 micro-Jy in a 65arcmin^2 field. One of the remaining radio sources is likely to be a radio lobe of a nearby Seyfert galaxy, and the four radio sources without counterparts could be spurious. All but five counterparts are brighter than magnitude 23.5 AB at 4.4 micron. A simple position match with radius 0.3 arcsec would have identified 198 of the counterparts but only in a 4.4 micron catalog created with aggressive deblending of multiple peaks within an object's brightness distribution into distinct catalog sources. The properties of the radio-host galaxies are mostly consistent with those found in Paper 1: the median redshift is 1.14, and the radio emission, calculated taking into account the non-linear dependence of radio luminosity on star-formation rate, is consistent with a star formation origin in ~79% of the sample. For the other ~21%, the radio flux could come from star formation hidden behind dust or from an active galactic nucleus. One difference from other studies of radio-source counterparts is that 66% of the radio hosts show at least one indication of an AGN's presence. The presence of AGN and of hidden star formation could be elucidated by monitoring for source variability, and the TDF is the field most suited to such observations.