NORTH6CM - 6cm Radio Catalog
Condon, J. J., Broderick, J. J. and Seielstad, G. A. 1989, AJ 97, 1064.
Langston, G. I., Heflin, M. B., Conner, S. R., Lehar, J., Carrilli, C. L., and Burke, B. F. 1990, ApJS 72, 621.
White, R. L., Becker, R. H., and Helfand, D. J. 1991, ApJ 371, 148.
The goal was to identify sources with peak intensities greater than 5 times the image RMS intensity level. Near declination +70 degrees the threshold is 20 mJy, while at 0 degrees it is typically 40 mJy. In fact, the RMS noise level varies on scales of 5 degrees or less. For instance, there is a ring of high noise at 64 degrees +/- 1 degrees declination which is approximately 30% higher than that just to the immediate north or south. Aside from these global effects, the completeness of the catalog suffers from local effects. The sensitivity to weak sources decreases in the vicinity of strong sources (> approximately 10 Jy) due to the sidelobe pattern of the 300-ft telescope. This is a serious problem along the entire galactic plane (abs(b) < 5 degrees) as well as near a number of isolated sources which are listed in Becker et al.
Declination Threshold (mJy) ---------------------------- 0 degrees 40 10 degrees 30 20 degrees 25 30 degrees 25 40 degrees 22 50 degrees 22 60 degrees 20 70 degrees 20
The separation between matched pairs is a measure of the combined positional errors in both catalogs. The Texas Survey has much better angular resolution in principle (approximately 5 arcsec) but has positional ambiguity due to interferometric sidelobes. To reduce this effect, we can limit ourselves to the 7,531 matched Texas source which are point sources with high quality flags. For this subset, 67% of the matches have separations of 25 arcsec or less while 95% are separated by less than 51 arcsec. The positional accuracy also depends on the 4.85-GHz flux density of the source in question. For sources with a 4.85-GHz flux density greater than 100 mJy, the 67% and 95% confidence error circles decrease to 18 and 38 arcsec respectively. These values are consistent with the positional accuracy for the survey estimated by CBS. To the extent that Texas sources contribute some of uncertainty in position, the above values should be taken as upper limits to the positional uncertainty in this catalog.
Determining the accuracy of the flux densities in the catalog is more problematic. A comparison between this catalog and the MIT--Greenbank 5-GHz Surveys (Langston et al. 1990; Bennett et al. 1986) indicates a general agreement in flux scales for brighter sources (>150 mJy) but some systematic differences for weak or extended sources.
The galactic latitude of the source.
The B-V color.
BROWSE classification code.
The Declination of the source.
This is "*" if the source is extended; otherwise, it is blank.
The 4.85-GHz flux (mJy) density of each source in mJy (the peak flux density for point sources and the integrated flux density for extended sources).
The galactic longitude of the source.
The 6cm name, constructed from RA and Dec in the format HHMM+DDSS, with A or B added at the end if needed to make the name unique.
NH Galactic Absorption from 21 cm (Note: All values are zero.)
The Right Ascension of the source.
The redshift of the source.
The spectral index between 80 cm and 6 cm for all sources with a counterpart in the Texas Survey. Apart from the uncertainty in the flux measurements, the spectral indices may also be affected by the nonsimultaneity of the two measurements and by the tendency of the Texas interferometric survey to underestimate the fluxes of sources larger than approximately 15 arcsec. Spectral indices are flagged using the wid_flag parameter with an asterisk for the 910 sources with 6 cm/80 cm position differences greater than 100 arcsec ; such matches have a reliability less than 80%.
This is blank if the source is not detected at 0.365-GHz.
The U-B color.
The V magnitude of the source.
This is "*" if the separation between 4.85- and 0.365-GHz positions is greater than 100 arcsec; otherwise, it is blank.