In April 1943, the ``amateur'' radio astronomer Grote Reber began the first systematic survey of the radio Universe. Using a backyard telescope with a beamwidth of 16 degrees operating at a frequency of 150 MHz, he spent most of the following year mapping the northern sky to a flux density threshold of a few thousand Janskys. The results, published in the Astrophysical Journal in the form of strip chart recorder reproductions (Reber 1944), revealed several areas of enhanced emission lying along the plane of the Milky Way, demonstrated that the emission centroid lay 30 degrees from the then-used zero point of Galactic longitude, and provided the first image of the Universe outside the traditional optical window.
Fifty years later, in April of last year, we began a second FIRST
survey at radio wavelengths. To produce our Faint Images of the Radio Sky
at Twenty-cm will take approximately the same amount of time as
Reber's work, but the final map will have more resolution elements and
will reach a sensitivity five million times greater. Using the
NRAO[NOTE: The National Radio Astronomy Observatory is operated by
Associated Universities, Inc., under cooperative agreement with the
National Science Foundation. ]
Very Large Array (VLA) in
its B-configuration, we will cover 10,000
of the
northern Galactic cap to a flux density limit of 1.0 mJy with
an angular resolution of better than
. The
principal data products will be (1) a sky map containing
pixels with an rms noise of
mJy, and (2) a 20 cm
source catalog with flux densities, subarcsecond positions, and
morphological information on over one million sources - in short, the
radio equivalent of the Palomar Sky Survey for 25%of the celestial
sphere.
We describe in this paper the motivation for a radio survey with this sensitivity and resolution, and place it in the context of other current and planned survey projects. We briefly outline the history of the FIRST project, from our original proposal in August of 1990 through the first round of observations in May of 1993. We describe in detail the survey design and present a comprehensive description of the data reduction and analysis system we have built and tested for generating the survey maps and catalogs. We demonstrate the realization of the FIRST survey's goals through the presentation of the 1039 coadded maps we have created from the 1993 data, and the numerous tests we have conducted to evaluate their astrometric, photometric, and morphological accuracy. A brief description of the radio source list we are extracting from the images is provided, although the catalog itself will be published separately. In the penultimate section, we present a precis of the numerous scientific problems which the FIRST survey will address. We conclude with our plan for distributing the fruits of the survey to the astronomical community.