The Molonglo Galactic Plane Survey. I. Overview and Images

The first-epoch Molonglo Galactic Plane Survey is a radio continuum survey made using the Molonglo Observatory Synthesis Telescope at 843 MHz with a resolution of 43''×43'' csc|δ|. The region surveyed is 245°≤l≤355°, |b|≤1.5°. The 13 9°×3° mosaic images presented here are the superposition of over 450 complete synthesis observations, each taking 12 h and covering a field of 70'×70' csc|δ|. The root-mean-square sensitivity over much of the mosaicked survey is 1-2 mJy beam-1 (1 σ), and the positional accuracy is ≈ 1''×1'' csc|δ| for sources brighter than 20 mJy. The dynamic range is no better than 250:1, and this also constrains the sensitivity in some parts of the images. The survey area of 330 deg2 contains well over 1.2×104 unresolved or barely resolved objects, almost all of which are extragalactic sources lying in the zone of avoidance. In addition, a significant fraction of this area is covered by extended, diffuse emission associated with thermal complexes, discrete H II regions, supernova remnants, and other structures in the Galactic interstellar medium.