What are these files about?

Hi, everybody!

I have been running a 7.3 database for a couple of weeks... and it has
grown by more than 20Gig on me within that interval...
I have a copy of the original database (I just copied all the files
before I started using it), and am trying to find out what exactly it is
that grew so much...

My understanding is that the files are identified by the oids the
objects they belong to...
I have no problem locating some of those objects in pg_class table and
matching them to my tables and indices...

But others for some reason cannot be matched... - there is no oid in
pg_class at all that would match the filename...
I am wonderring if somebody could please let me know what are these
unmatched files and how I can locate the actual objects that are using them?

Thank you very much!

Dima