Mid-infrared identification of 6 cm radio-source counterparts in the extended Groth Strip

摘要

A new 6 cm survey of almost 0.6 deg(2) to a limit of 0.55 mJy beam(-1) (10 sigma) 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 less than or similar to z less than or similar to 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 mu m colors and a small range of 8 mu m magnitudes. This separation should be useful in classifying galaxies found in other radio surveys.