A New Complete Sample of Submillijansky Radio Sources: An Optical and Near‐Infrared Study

The Very Large Array (VLA) has been used in C-configuration to map an area\~0.3 square degrees at 1.4 GHz with 5sigma sensitivities of 0.305, 0.325,0.380 and 0.450 mJy/beam over four equal subareas. Radio properties arepresented for 62 detected sources. Deep optical imaging to Gunn r~25 mag usingthe Hale 5-m telescope covering ~0.21 square degrees is reported for a subsetof 43 sources. This optical follow-up is much deeper than that of existinglarger area radio surveys of similar radio sensitivity. Archival J, H andK-band photometry from the Two-Micron All Sky Survey (2MASS) is also presented.Using a robust likelihood-ratio technique, we optically identified 26 radiosources with probabilities >80%. Nine are uncertain/ambiguous detections andeight are empty fields. Comparisons with a stellar synthesis model thatincludes radio emission and dust reddening suggests that thenear-infrared--to--optical emission in a small, bright sub-sample is reddenedby `optically-thin' dust with absorption A_V ~ 2-2.5 mag, regardless ofmorphological type. This is consistent with other, more direct determinationsof absorption. The radio--to--optical(--near-infrared) flux ratios ofearly-type galaxies require significant contamination in the radio by an activegalactic nucleus (AGN), consistent with the current paradigm. Using our simplemodeling approach, we also discuss a potential diagnostic for selectingUltraluminous Infrared Galaxies (ULIGS) to z~1.6 from microJansky radiosurveys.