Deleting large objects from database. - Mailing list pgsql-sql

I have column with large objects in table named my_table.
After SQL command:  delete from my_table;
they are still files xinv* and xinx* in directory ./data/base/my_db.
Have I delete this files from operating system?
What is wrong? I hope thats is only my ignorance?

Best regards,Marcin Czarny