3 Database

In Table 1 we present the information available for the B3-VLA sample. Columns 1 and 2 list the frequency and reference to the relevant paper, Col. 3 gives the percentage of sources for which the data are available.

  

Table 1: Measured flux densities of B3-VLA sources

3.1 151 MHz data

These flux densities were obtained by cross-correlating the 6C survey (Hales et al. 1988) with the B3-VLA sample. The search radius used was 100$^{\prime\prime}$, which corresponds to a combined 3-$\sigma$ error for the fainter sources. We do not expect any chance coincidences, owing to the low source density at 151 MHz (4.1 sources per square degree). The values quoted in Table 2 are the peak flux densities for sources with an angular extent < 100$^{\prime\prime}$ (extents taken from Vigotti et al. 1989), and the integrated ones (listed in the 6C, Hales et al. 1988) for larger sources. The error in the same table is computed as a constant term of 40 mJy, plus a 5% contribution due to the uncertainty of the flux density scale.

Since these data are on the flux scale of Roger et al. (1973, RBC), we used the spectral indices reported by these authors to calculate the flux density of their calibrator sources at 178 MHz. In this way we could compare the scale of Roger et al. (1973) with the one of Kellermann et al. (1969, KPW). The ratio between these two flux density scales is KPW/RBC = 0.96. Baars et al. (1977, BGPW) report a ratio of BGPW/KPW = 1.051. Thus, the ratio BGPW/RBC turns out to be 1.008; therefore no correction was applied at 151 MHz.

3.2 327 MHz data

For sources with an angular extent < 50$^{\prime\prime}$ we cross-correlated the B3-VLA positions with the WENSS source list (Rengelink et al. 1997) using a window of 11$^{\prime\prime}$ in right ascension and 22$^{\prime\prime}$ in declination. For the more extended ones we used a window of 40$^{\prime\prime}$ in right ascension and 80$^{\prime\prime}$ in declination. The total area searched was 0.03 square degrees. The WENSS source density is about 21.3 per square degree so that the contamination by chance coincidences is negligible. For the flux density errors we used the formula given by Rengelink et al. (1997), with a noise contribution of 4.5 mJy (which is the average value in the B3-VLA area), plus 4% due to the calibration uncertainty $\Delta_{\rm cal}$.

Sources with a complex structure (as marked in the WENSS catalogue; Rengelink et al. 1997) were inspected directly on the WENSS maps, and their flux densities computed with the AIPS task TVSTAT. For these sources the errors $\Delta S$ were computed as follows:

$$\Delta S = \sqrt {(\Delta_{\rm cal} \cdot S)^2 +\sigma_{\rm l}^2\cdot \frac{A_{\rm s}}{A_{\rm b}}}\cdot$$

Here $\sigma_{\rm l}$ is the local noise in the map, $A_{\rm s}$ the area covered by the radio source, and $A_{\rm b}$ is the beam area. The flux densities in the WENSS survey are on the scale of Baars et al. (1977).

3.3 408 MHz data

The flux densities were taken from the B3 survey, except for extended sources for which an integrated flux density was used (Vigotti et al. 1989). For the computation of the errors we used 35 mJy as the constant term and 3$\%$ for the term proportional to the source flux density (Ficarra et al. 1985). The flux density scale of these data is based on 3C123, and agrees with the scale of Baars et al. (1977) to within 2$\%$. Therefore, no correction was applied.

3.4 1.4 GHz data

The flux densities were computed from the maps of the NRAO VLA SKY Survey (NVSS, Condon et al. 1998), centred on the B3-VLA positions using an automatic two-component Gaussian fit algorithm similar to the AIPS task JMFIT. For the unresolved sources the difference between our flux density and that listed in the NVSS catalogue is negligible (< 2%). The errors were calculated with the formula of Condon et al. (1998), where the noise and confusion term is 0.45 mJy/beam and the calibration uncertainty is 3%.

For the extended and complex sources the flux densities were computed using the AIPS task TVSTAT. Their errors were computed as above (Sect. 3.2). The flux densities are on the scale of Baars et al. (1977).

3.5 4.85 GHz data

All sources not available in the literature (Kulkarni et al. 1990; Gregory et al. 1996) have been observed as described in Sect. 2. The flux densities of Kulkarni et al. (1990), and those observed by us before August 1995 were shifted from 4.75 GHz to 4.85 GHz using the spectral index of the radio source. For the flux densities presented in this paper we adopted 1.0 mJy as the noise contribution, and 2% as the contribution proportional to the flux density. Another 0.45 mJy is added to account for source confusion (Reich 1993). For the data of Kulkarni et al. (1990) the errors are 2 mJy and 2%, respectively. The errors of the flux densities taken from Gregory et al. (1996) are listed in the GB6 catalogue. In 2 cases, 1412+397 and 2341+396B, the sources could not be separated from a closeby confusing source. We used the flux densities from our measurements (45.8%). In cases where those were not available the flux densities reported by Kulkarni et al. (1990; 42.4%) or Gregory et al. (1996; 11.8%) were taken.

The GB6 maps of the sources with extension larger than 70$^{\prime\prime}$ were downloaded using SkyView. In addition, the most extended ones (0136+396, 0157+405A, 0248+467, 0703+426A, 1141+374, and 1309+412A) were mapped in Effelsberg. In all cases the flux densities were determined with AIPS task TVSTAT and the errors were calculated as described above (Sect. 3.2). The flux densities are on the scale of Baars et al. (1977).

3.6 10.6 GHz data

In Table 2 we list the integrated flux densities as well as the errors computed using the formula presented in Paper I. Here, the noise term is 0.8 mJy, confusion contributes 0.08 mJy, and the term proportional to the flux is 2%. The flux densities are on the scale of Baars et al. (1977).