Through the course of these investigations, the X-ray background was determined to have originated from the central supermassive black holes of distant galaxies, and a better characterization of Type II quasars was obtained.[Note 1] The CDFS discovered over 300 X-ray sources, many of them from "low luminosity" AGN lying about 9 billion light years away. The study also discovered the then most distant Type II quasar, lying at redshift z=3.7, some 12 billion light years away.[1]