VLA 1.4GHz observations of the GOODS-North Field: Data Reduction and Analysis

TL;DR

This paper presents deep 1.4GHz radio observations of the GOODS-North field, cataloging over 1,200 sources, demonstrating advanced data reduction techniques, and analyzing source counts to explore the confusion limit and implications for the cosmic microwave background.

Contribution

It introduces new data reduction methods for wide-field radio imaging achieving high dynamic range and provides detailed source counts near the confusion limit.

Findings

Nearly Euclidean source counts below 100uJy

Median source diameter of ~1.2"

Confirms the natural confusion limit near ~1uJy

Abstract

We describe deep, new, wide-field radio continuum observations of the Great Observatories Origins Deep Survey -- North (GOODS-N) field. The resulting map has a synthesized beamsize of ~1.7" and an r.m.s. noise level of ~3.9uJy/bm near its center and ~8uJy/bm at 15', from phase center. We have cataloged 1,230 discrete radio emitters, within a 40' x 40' region, above a 5-sigma detection threshold of ~20uJy at the field center. New techniques, pioneered by Owen & Morrison (2008), 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 100uJy with a median source diameter of ~1.2". This adds to the evidence presented by Owen & Morrison (2008) that the natural confusion limit may lie near ~1uJy. 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 1uJy else the cosmic microwave background temperature would increase above 2.7K at 1.4 GHz.