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The AGN Catalog

The Catalog

The Active Galactic Nuclei (AGN) catalog is heavily based on A Catalogue of Quasars and Active Nuclei (7th Edition), ESO Scientific Report No. 17, by Véron-Cetty & Véron (1996) [VV96]. That includes 11,442 quasars and active galaxies, and gives optical magnitudes, redshift, and some radio information. To this we have added: 1. the BL Lac catalog of Padovani & Giommi (1995), updated with BL Lacs discovered in 1996 (for a total of 265 sources); 2. the radio galaxies in the 1 Jy, S4, and S5 radio catalogs, mostly not included in VV96. The resulting database, which totals 12,021 AGN, was also cross-correlated with various radio catalogs providing 6 cm data, namely the PKS database, the PMN survey , the GB6 catalog, the 1 Jy, S4, and S5 radio catalogues. Individual radio fluxes for radio-quiet AGN not included in radio catalogs (radio fluxes < 1 - 30 mJy), taken from the literature, were also added. The V magnitudes in VV96 are actually mostly B or photographic magnitudes when no (B-V) value is available. Therefore, for objects without (B-V) colors, V magnitudes have been derived from the given values by subtracting (B-V) values typical of the class to which an object belongs to, unless the reference was to a paper which gave V magnitudes directly. One should remember that most AGN are variable so the reported V magnitudes should be taken only as indicative. (See Padovani (1997) and Padovani et al. (1997) for some astrophysical applications of an extended version of the catalog.)

The Classification

The classification is based mostly on the one given by VV6, to which the user is referred to, with some differences and additions. Namely:
  • AGN UNCLASSIFIED: unclassified sources in Table 3 of VV96 (which includes "active galaxies").
  • BL LAC: sources appearing in the BL Lac catalogue of Padovani & Giommi (1995), updated with BL Lacs discovered in 1996.
  • LINER: classified as S3 (or Seyfert 3) in VV96.
  • QSO: this includes all quasars appearing in Table 1 of VV96, defined by a value of the blue absolute magnitude brighter than -23; for these objects a sub-classification as radio-loud or radio-quiet has been done, based on the two point spectral index alpha_ro (defined here between 5000 Angstroms and 6 cm [5 GHz]). Objects with (K-corrected) alpha_ro > 0.19 (corresponding to the "standard" dividing value of radio flux to optical flux > 10) have been called radio-loud. For the purpose of calculating alpha_ro, V magnitudes have been corrected for extinction following Wilkes et al. (1994) and for the presence of emission lines according to Natali et al. (1998). Radio-loud Seyfert 1 galaxies have been included with the radio-loud QSO, where they belong according to unified schemes for AGN (see, e.g., Urry & Padovani 1995). Note that sometimes radio fluxes are available only at wavelengths other than 6 cm (e.g., from the FIRST or NVSS surveys). In these cases the radio flux at 6 cm used to calculate alpha_ro has been derived by extrapolating the flux assuming a radio spectral index typical of the class to which an object belongs to.
    • QSO (NO V-MAG): 196 QSO without (believe it or not) V magnitude;
    • QSO RADIO-LOUD; QSO (and Seyfert 1 galaxies) with alpha_ro > 0.19 (includes a few QSO without V magnitude but radio flux > 0.5 Jy);
    • QSO RADIO-QUIET; QSO with alpha_ro <= 0.19.
  • RADIO GALAXY; from the 1 Jy, S4, and S5; also, radio-loud Seyfert 2 galaxies were checked individually and classified as radio-galaxies if appropriate (radio galaxies are classified as Seyfert 2 galaxies in VV96).
  • SEYFERT TYPE 1; sources in Table 3 of VV96 classified as S1 (excluding objects with broad lines in polarized light only); radio-loud Seyfert 1 galaxies are included with the radio-loud QSO (see above).
  • SEYFERT TYPE 2; sources in Table 3 of VV96 classified as S2, plus S1 in VV96 with broad lines in polarized light only (classified as S1 in VV96).
  • SEYFERT?; sources in Table 3 of VV96 classified as S or S?.
  • STARBURST GALAXY; sources in Table 3 of VV96 classified as H2.

Useful Hints

(work in progress)


Classification of astronomical objects is a complex subject and in many cases the assignement of an object to a given class can be a matter of dispute. We have done our best to be as objective as possible but are obviously open to comments and suggestions about the catalog. These should be sent, along with any questions, to Archive hotseat.