pg_psort files

I have a fairly simple database (two tables and a few indecies). In
the data/base/xxxx directory I find the following files:

-rw------- 1 postgres postgres 7734146 Dec 14 06:36 pg_psort.13268.0
-rw------- 1 postgres postgres 7707487 Dec 14 06:36 pg_psort.13268.1
-rw------- 1 postgres postgres 7776602 Dec 14 06:36 pg_psort.13268.2
-rw------- 1 postgres postgres 936026112 Dec 14 07:20 pg_psort.13268.3
-rw------- 1 postgres postgres 8208384 Dec 14 06:36 pg_psort.13268.4
-rw------- 1 postgres postgres 15699116 Dec 14 06:36 pg_psort.13268.5
-rw------- 1 postgres postgres 19002244 Dec 14 06:36 pg_psort.13268.6
-rw------- 1 postgres postgres 2097152 Dec 9 06:33 pg_psort.25350.0
-rw------- 1 postgres postgres 2146304 Dec 9 06:33 pg_psort.25350.1
-rw------- 1 postgres postgres 2277376 Dec 9 06:33 pg_psort.25350.2
-rw------- 1 postgres postgres 1597440 Dec 9 06:33 pg_psort.25350.3
-rw------- 1 postgres postgres 1064960 Dec 9 06:33 pg_psort.25350.4
-rw------- 1 postgres postgres 1327104 Dec 9 06:33 pg_psort.25350.5
-rw------- 1 postgres postgres 0 Dec 9 06:32 pg_psort.25350.6

I have another database that is almost identical on a different
machine. There are no pg_psort.xxxx files there. I am wondering:

1. What are these files?
2. Do I need them?
3. If I don't need them is it safe to remove them?

--
==================================================================
Steven Saner SouthWind Internet Access, Inc.
ssaner(at)southwind(dot)net Systems/Network Administrator
http://www2.southwind.net/~ssaner http://www.southwind.net
263-7963 Wichita (800)525-7963