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" x 43" csc\delta\. The region surveyed is 245 degrees less than or equal to l less than or equal to 355 degrees, \b\ less than or equal to 1.5 degrees. The 13 9 degrees x 3 degrees mosaic images presented here are the superposition of over 450 complete synthesis observations, each taking 12 h and covering a field of 70' x 70' csc \delta\. The root-mean-square sensitivity over much of the mosaicked survey is 1-2 mJy beam(-1) (1 sigma), and the positional accuracy is approximate to 1" x 1" csc\delta\ 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 deg(2) contains well over 1.2 x 10(4) 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.