WB1400 (E0): 1400 MHz Northern Sky Catalog, Dec 1991 (19941109)
FILE: wb1400.e0 (31524 sources)
CONTENTS: Green Bank 300-foot (91m) 1.4 GHz Radio Survey, -6 <= Dec <= +83
DATASET: This file comes in HyperSky dataset E-6, version 19941109. Availability on HyperSky CD-ROM: Vol. 2 (1995)
DESCRIPTION: This datafile contains the 1400 MHz (1.4 Ghz or 20cm) Northern Sky Survey, distribution version of 4 December 1991, by R.L. White and R.H. Becker, as discussed in 1992 Ap.J.Supp., 79, 331. The survey was carried out with the Green Bank 300-ft (91 m) radio telescope, and contains 31524 discrete sources. The sources range in strength from 80 to 61100 mJy (milli-Janskys), and cover a declination range of from -6.3 to +83.3 (equinox 2000).
Lower radio frequencies such as 1400 MHz are typically dominated by emissions from nonthermal sources. In the extragalactic realm, such sources are associated with active galaxies having suspected central black holes, emission jets, and the like.
DATA: The HyperSky datafiles contain the following data from the catalog:
POSITION: Right Ascension and Declination are based on the catalog 1950 positions, precessed to equinox 2000. Catalog positions were provided to an accuracy of 0.1 second in Right Ascension and 1" in declination.
MAG: No magnitudes or equivalents were provided in the catalog. A set of artificial magnitudes is provided, however, in the HyperSky catalog strictly to allow use of HyperSky's limiting-magnitude controls. In this way, users can display only those sources above a desired threshold. The artificial magnitude system is based on the relation (from Pogson) used to define visual magnitudes:
m1 - m2 = 2.5 * log10(S1/S2)
where { m1, m2 } are magnitudes, and { S1, S2 } are source strengths. For the HyperSky catalog, the brightest source (S1 = 61100 mJy) is arbitrarily assigned the magnitude m1 = 1.0. Given this, any other source S2 can have its relative magnitude, m2, derived using the relation:
m2 = 1.0 + 2.5 * log10 (61100/S2);
In this system, the faintest catalog source (80 mJy) has a magnitude of 8.2. The following table summarizes the relation between magnitude and source strength for catalog extremes and intermediate magnitudes:
Magnitude Source Strength (mJy)
----------|----------------------
1.0 61100 (brightest catalog source)
2.0 24324
3.0 9684
4.0 3855
5.0 1535
6.0 611
7.0 243
8.0 97
8.2 80 (faintest catalog source)
With the above table, a user can set HyperSky's limiting magnitude (for emission sources) to mask out catalog sources below a desired strength. Except for this use, the derived source magnitudes have NO significance. It should be emphasized again that the magnitudes are NOT provided in the original catalog; only the source strengths are fundamental catalog values.
IDENTIFICATION: The derived source name, constructed from the equinox 1950 RA, Dec HHMM+DDMM with A or B added at end if needed to make the name unique. When a source matches a source in the 4850 MHz (6cm) catalog of Becker, White, & Edwards (1991, ApJSupp 75, 1) the 6cm name and position (good to 40" at the 90% confidence level) are used. Sources without a 6cm counterpart have names ending in L; their positions are accurate only to 160" at the 90% confidence level.
COMMENTS: The comment line contains the following information, provided if available for each radio source:
* The 1400 MHz (20cm) flux strength in mJy (milli-Janskys). An asterisk follows if the source is extended at 1400 MHz.
* In parentheses following the above value are, if available, two additional flux values for the source: The 4850 MHz (6cm) flux strength, from Becker et al (1991); and following it, the 365 MHz (80cm) flux strength, from the Texas Survey by Douglas et al (private communication). If either of these values is missing, a dash will appear for it. Either flux value can be followed by an asterisk if the source is extended at the given frequency.