"Counting all the SHEEP": A summary of the past and present work associated with ASCA’s The Search for the High-Energy Extragalactic Population (SHEEP) survey.

Abstract

SHEEP is the Search for the High-Energy Extragalactic Population, a survey of X-rays sources found in 5-10 keV band images from the ASCA satellite. Because hard X-rays are difficult to obscure, SHEEP provides a largely unbiased accounting of the AGN population. We have been identifying SHEEP using new high-resolution Chandra images, and following up with deep optical imaging from Greece and near-infrared imaging from Wyoming. Spectral classifications are obtained at NOAO 4-meter telescopes. Our initial work shows a wide variety of optical classes, ranging from QSOs to optically normal galaxies (despite their high X-ray luminosities). We have also identified several high-redshift quasar pairs, which is intriguing given the size of the sample. Completion of identifications and classifications will permit us to finally "count the SHEEP" and provide a better picture of the AGN population and the sources contributing to the X-ray background.