All the objects in the database, galaxies, stars, clusters, ..., are
indexed with their pgc number.
Historically, the pgc numbering was created to unify the names
of the galaxies when the database project started in 1983. The first effort
was to cross-identify the early catalogues of galaxies, like
the MCG, UGC ..., and it resulted in the publication of the
Principal Catalogue of Galaxies
(Paturel et al. 1989). This catalogue counted 73097 entries corresponding
to what was believed to be galaxies.
The project continued, new objects were identified and previous errors
corrected. The main line of improvement was the precision of the astrometry,
which evolved from about 1 arcmin in 1990 to about 1 arcsec now.
With the publication of high quality catalogues, the necessity of maintening
PGC names vanished in the 2000s, and we stopped to systematically
publish PGC names. The database contains at present 1.7 million PGC names.
Still, all the objects in the database (about 5 millions) have a pgcnumber which is used as a unique identification across the different
tables. This number should not be used to build a name, since it
would not be recognized by any database, including HyperLeda.
To identify objects in publications, it is recommended to use (i) a name and
(ii) a position.
Hyperleda provides objname, which is the
best suited name amongst all designations available for an object because
it is the most likely to be widely recognized.