Introduction

 

The FIRST survey of the north Galactic cap began in the spring of 1993. Using the VLA at a frequency of 1.4 GHz, the survey is slated to cover 10,000 square degrees to a sensitivity of  mJy with an angular resolution of ; details are presented in Becker, White & Helfand (1995; hereafter, [BWH95]). The primary data product of the survey is a set of overlapping images, which are, in turn, coadded to achieve uniform sky coverage. The coadded images are available over the Internet from several sources (see the FIRST home page at http://sundog.stsci.edu for details.) However, each such image requires  Mbytes of storage in full 32-bit format, hence the set of 5000 images already available is beyond the storage capacity of most users. To make the results of the survey more accessible, we have derived from the images a source catalog which will meet most of the needs of most astronomers.

This paper describes the methodology for generating the radio source list and discusses the reliability and accuracy of the catalog. We begin by presenting the basic parameters of the FIRST images and the coverage the survey has achieved to date (§ 2). In § 3, we describe the algorithm we have developed to extract sources from the images; this is followed (§ 4) by a description of the catalog generation procedure and an annotated sample catalog page (the catalog itself is available on the World-Wide Web -- see below). Section 5 includes a brief summary of the tests we have performed to characterize the accuracy of the astrometric, photometric, and morphological parameters of the catalog entries, and a discussion of the catalog's reliability and completeness. Subsequent sections explore the relation we observe (§ 6), and, as an illustration of the catalog's utility, the rate of matches we obtain between FIRST sources and various catalogs from other wavelength regimes (§ 7). We conclude with a summary that includes instructions for access to the current catalog and subsequent updates (§ 8).