Temporary tables and miscellaneous schemas

Whenever I create a temporary table, with something like

CREATE TEMPORARY TABLE temptable1 AS SELECT * FROM paid.ad_hoc_query;

New schemas appear, with names like "pg_temp_1". I guess the appearance
of these schemas with "temp" in the name indicates that they are
"temporary" schemas and related to the temporary table creation, but the
schemas persist even after the end of the session in which the temporary
table was created.

What's up with these miscellaneous schemas? Are they in fact related to
the creation of temporary tables? Should they disappear when the session
closes, as should the temporary table? If they continue persisting after
the session closes, how do I get rid of them?

~Berend Tober