A new complete sample of submillijansky radio sources: An optical and near-infrared study

The Very Large Array has been used in C configuration to map an area simila r or equal to 0.3 deg(2) at 1.4 GHz with 5 sigma sensitivities of 0.305, 0. 325, 0.380, and 0.450 mJy beam(-1) over four equal subareas. Radio properti es are presented for 62 detected sources. Deep optical imaging to Gunn r si milar or equal to 25 mag using the Hale 5 m telescope covering similar or e qual to 0. 21 deg(2) is reported for a subset of 43 sources. This optical f ollow- up is much deeper than that of existing larger area radio surveys of similar radio sensitivity. Archival J-, H-, and K- band photometry from th e Two- Micron All Sky Survey is also presented. Using a robust likelihood r atio technique, we optically identified 26 radio sources with probabilities greater than or equal to 80%, nine with uncertain/ ambiguous detections, a nd eight with empty fields. Comparisons with a stellar synthesis model that includes radio emission and dust reddening suggest that the near- infrared - optical emission in a small, bright subsample is reddened by "optically t hin" dust with absorption A(V) similar or equal to 2-2.5 mag, regardless of morphological type. This is consistent with other, more direct determinati ons of absorption. The radio- optical(- near- infrared) flux ratios of earl y- type galaxies require significant contamination in the radio by an activ e galactic nucleus, consistent with the current paradigm. Using our simple modeling approach, we also discuss a potential diagnostic for selecting ult raluminous infrared galaxies to z similar or equal to from microjansky radi o surveys.