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

January 2001 • 2001PASP..113...10M

Authors • Masci, Frank J. • Condon, J. J. • Barlow, T. A. • Lonsdale, C. J. • Xu, C. • Shupe, D. L. • Pevunova, O. • Fang, F. • Cutri, R.

Abstract • The Very Large Array has been used in C configuration to map an area ~=0.3 deg² at 1.4 GHz with 5 σ sensitivities of 0.305, 0.325, 0.380, and 0.450 mJy beam^-1 over four equal subareas. Radio properties are presented for 62 detected sources. Deep optical imaging to Gunn r~=25 mag using the Hale 5 m telescope covering ~=0.21 deg² is reported for a subset of 43 sources. This optical follow-up is much deeper than that of existing larger area radio surveys of similar radio sensitivity. Archival J-, H-, and K-band photometry from the Two-Micron All Sky Survey is also presented. Using a robust likelihood ratio technique, we optically identified 26 radio sources with probabilities >~80%, nine with uncertain/ambiguous detections, and 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 thin'' dust with absorption A_V~=2-2.5 mag, regardless of morphological type. This is consistent with other, more direct determinations of absorption. The radio-optical(-near-infrared) flux ratios of early-type galaxies require significant contamination in the radio by an active galactic nucleus, consistent with the current paradigm. Using our simple modeling approach, we also discuss a potential diagnostic for selecting ultraluminous infrared galaxies to z~=1.6 from microjansky radio surveys.

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Roc Cutri

IPAC Deputy Director

Dave Shupe

Senior Scientist