Mid-infrared identification of 6 cm radio-source counterparts in the extended groth strip

A new 6 cm survey of almost 0.6 deg² to a limit of 0.55 mJy beam^-1 (10 σ) finds 37 isolated radio sources and seven radio-source pairs (not necessarily physical companions). Infrared Array Camera (IRAC) counterparts are identified for at least 92% of the radio sources within the area of deep IRAC coverage, which includes 31 isolated sources and six pairs. This contrasts with an identification rate of <74% to R < 23.95 in visible light. Eight of the IRAC galaxies have power-law spectral energy distributions, implying that the mid-infrared emission comes from a powerful active galactic nucleus (AGN). The remaining 26 IRAC galaxies show stellar emission in the mid-infrared, probably in most of these galaxies because the stellar emission is bright enough to outshine an underlying AGN. The infrared colors suggest that the majority of these galaxies are bulge-dominated and have redshifts 0.5 ≲ z ≲ 1. Visible spectra from the DEEP2 Redshift Survey, available for 11 galaxies, are consistent with this suggestion. The IRAC galaxies fall into two distinct groups in a color-magnitude diagram. One group (the "stripe") includes all the AGNs. The other group (the "blue clump") has blue 3.6-8 μm colors and a small range of 8 μm magnitudes. This separation should be useful in classifying galaxies found in other radio surveys.