Very large array 1.4 GHz observations of the goods-north field: Data reduction and analysis

摘要

We describe deep, new, wide-field radio continuum observations of the Great Observatories Origins Deep Survey-North field. The resulting map has a synthesized beam size of ～1.7 and an rms noise level of ～3.9 μJy beam~(-1) near its center and ～8 μJy beam~(-1) at 15′ from phase center. We have cataloged 1230 discrete radio emitters, within a 40′ × 40′ region, above a 5σ detection threshold of ～20 μJy at the field center. New techniques, pioneered by Owen & Morrison, have enabled us to achieve a dynamic range of 6800:1 in a field that has significantly strong confusing sources. We compare the 1.4 GHz (20 cm) source counts with those from other published radio surveys. Our differential counts are nearly Euclidean below 100 μJy with a median source diameter of ～1.2. This adds to the evidence presented by Owen & Morrison that the natural confusion limit may lie near 1 μJy. If the Euclidean slope of the counts continues down to the natural confusion limit as an extrapolation of our log N-log S, this indicates that the cutoff must be fairly sharp below 1 μJy else the cosmic microwave background temperature would increase above 2.7 K at 1.4 GHz.