Appendix I: The Master Catalog

The Master Catalog contains the original data taken from the source references of Table 1. Due to the extensive amount of information, we have divided for convenience the Master Catalog into 11 sub-catalogs. We give hereafter the description of the structure of each of these compilations while, for a general overview about the content of the sub-catalogs, we refer the reader to Sect. 2.5.

As mentioned in the main text (Sect. 2.5), each sub-catalog (except for Sub-catalog 1) has 37 columns and 1442 entries corresponding to the total number of sources. The columns are in order of increasing frequency of observation and, at each frequency, the columns are in alphabetical order of the references in Table 1. In all sub-catalogs, a null entry corresponds to no information available from the source reference.

Sub-catalog 1 lists only source coordinates, notes about the environment and radio/optical couterparts. For its content specificy, it presents a peculiar structure with respect to the other sub-catalogs. In detail:

- Column 1: source-numbering (records from 1 to 1442)
- Columns 2-3: Galactic coordinates, l and b
- Columns 4-6: celestial coordinates: RA - J2000
- Columns 7-9: celestial coordinate: DEC - J2000
- Column 10: general remarks - $\rm C= complex$ field, $\rm S= strong$ source nearby, $\rm X=strong$ source nearby (>10 Jy), radio or optical counterpart. This flags follow the definitions given by Kuchar $\&$ Clark (1997) according to which a source is in a complex field when there are two or more sources within either $2\times\Theta_{\rm obs}$ (i.e, four source radii) or $2\times\Theta_{\rm beam}$, whatever is larger, or with a strong and/or much stronger source nearby.

As for the counterpart in other wavebands, for the case of the radio identifications: Ke refers to Kesteven (1968); NRAO to Pauliny-Toth (1966); W to Westerhout (1958); 3C to Third Cambridge Catalog (Bennett 1962) and 4C to Fourth Cambridge Catalog (Gower et al. 1967; Pilkington et al. 1965).

For the optical identifications, the Mársalková Catalog 1974 has been consulted. In this case: BBW refers to Bok-Bester-Wade (1955); DWB to Dickel-Wendker-Bieritz (1969); Ge (a) to Georgelin-Georgelin (1970a); Ge (b) to Georgelin-Georgelin (1970b); Ge (c) to Georgelin-Georgelin (1970c); G to Gum (1955); H to Hoffleit (1953); RCW to Rodgers-Campbell-Whiteoak (1960); S to Sharpless (1959). Moreover, M stands for Messier Catalog; NGC for Dreyers'New General Catalog and IC for the Index Catalog.

Sub-catalog 2 to sub-catalog 11 have the following structure:

- Column 1: source-numbering (records from 1 to 1442);
- Columns 2-3: Galactic coordinates, l and b;
- Columns 4-6: celestial coordinates: RA - J2000;
- Columns 7-9: celestial coordinate: DEC - J2000;
- Columns 10-11: 1.4 GHz - Altenhoff et al. (1970), Felli $\&$ Churchwell (1972);
- Columns 12-23: 2.7 GHz - Altenhoff et al. (1970), Beard (1966), Beard $\&$ Kerr (1969), Beard et al. (1969), Day et al. (1969), Day et al. (1970), F $\ddot{\rm u}$rst et al. (1987), Goss $\&$ Day (1970), Reich et al. (1986), Thomas $\&$ Day (1969a), Thomas $\&$ Day (1969b), Wendker (1970);
- Column 24: 3.9 GHz - Berlin et al. (1985);
- Columns 25-26: 4.8 GHz - Kuchar $\&$ Clark (1997);
- Columns 27-34: 5 GHz - Altenhoff et al. (1970), Altenhoff et al. (1979), Caswell $\&$ Haynes (1987), Downes et al. (1980), Mezger $\&$ Henderson (1967), Reifenstein et al. (1970), Wilson et al. (1970), Wink et al. (1982);
- Column 35: 14.7 GHz - Wink et al. (1983);
- Column 36: 15 GHz - Wink et al. (1982);
- Column 37: 86 GHz - Wink et al. (1982).

Note on sub-catalog 2 and sub-catalog 4: these sub-catalogs, including data on flux and angular diameters, always list values corrected for the instrument beam. Their complementary sub-catalogs are sub-catalog 3 and 5 quoting relative (%) errors.

Note on sub-catalog 6 to 11: these sub-catalogs list line velocity data. Observations may refer to frequencies other than those for the continuum data. In particular:

- Columns 25-26: Kuchar $\&$ Clark quote continuum data at 4.85 GHz and line data from Reifenstein et al. (1970) and from Wilson et al. (1970) at 5 GHz (H109$\alpha$) and from Lockman (1989) at 10 GHz (H85$\alpha$, H87$\alpha$ and H88$\alpha$);
- Column 28: Altenhoff et al. (1979) quotes continuum data at 5 GHz while line data are taken from Lockman (1989) at 10 GHz (H85$\alpha$, H87$\alpha$ and H88$\alpha$);
- Columns 29-33: Caswell $\&$ Haynes (1987), Downes et al. (1980), Mezger $\&$ Henderson (1967), Reifenstein et al. (1970), Wilson et al. (1970) quote both continuum and line data at 5 GHz (H109$\alpha$, H110$\alpha$);
- Columns 34-36-37: Wink et al. (1982) quotes continuum data at 5/15/86 GHz and line data at 8.9/14.7 GHz (H90$\alpha$ and H76$\alpha$).