This document defines the catalog entries describing
the VLA-FIRST Data Archive as delivered to STScI by
the FIRST Team.
Archive Background:
The FIRST survey (Faint Images of the Radio Sky at Twenty-cm) is a high angular resolution survey of the North Galactic Cap intended to match the 10,000 deg**2 survey area of the Sloan Digital Sky Survey.
Observation are made in the VLA's B configuration operating at frequencies of 1365 and 1425 MHz in the bandwidth synthesis mode. The synthesized beam has a FWHM of 5.4". Each field is observed for 3 minutes, resulting in a typical image rms of <0.15 mJy/beam.
Details of the survey design, pipeline processing algorithms, and catalog generation may be found in Becker et.al. 1995; this paper, along with further information on FIRST, is retrievable via the FIRST web page http://sundog.stsci.edu. Users interested in deriving quatitative information from the maps for scientific purposes are advised to read the FIRST paper first. Questions or comments on the FIRST survey should be addresssed to Bob Becker.
General Results Options
Most mission search results pages have the following general
features/options. (Note that the sorting, paging and VOPlot
options all require javascript to be turned on.):
Clicking on the column headings at the TOP of the
results table will sort the returned results based on the selected
field. Clicking the column heading a second time will sort the
results in descending order. Note that a bug currently exists
whereby exponents are ignored in numbers using exponential notation
(e.g., 6.3E-3 is sorted as if it were 6.3). Since most tables
don't include exponential numbers this is not felt to be a major
problem.
Clicking one of the column headings
at the END of the results table (or clicking the
"columns help" link at the top of the page) will display
help information about the search results page and the displayed
columns (i.e., this page).
By default, results are shown with 50 entries per page, with links
to additional pages if more than 50 entries were returned. The number of
rows per page can be modified using the "Records per Page" form element
on the search form. The total number
of entries returned is set by the "Maximum Records" value from the search page.
(Note that when the total number of returned rows is
a multiple of 50, an extra page is displayed with no entries.)
One numerical column can be plotted versus another using VOPlot.
For some missions, thumbnail images of the reurned entries
can be displayed by clicking the link listed just below the VOPlot link.
The mark column, as described below, can be used to plot spectra
and download files.
The Data ID consists of the J2000 coordinates of the field center
in the format HHMMM+/-DDMMM (with implied decimal points before the final M's)
followed by a character that gives some idea of the epoch for observation and
processing.
Clicking on the Data ID entry in the search results table will
bring up a dialog box permiting download of the VLA data.
The angular separation in arcminutes between the observation
and the search center (the coordinates you're searching on). This is
calculated during the search, and the search results are sorted in order
of increasing angular separation.
It also means that you can give a search radius like, say, 2 .. 8
to find all observations between 2 and 8 arcminutes from some position.
This could be used, for example, to find the observations in the vicinity of a bright 3C radio source.