The Chandra multi-wavelength project (ChaMP): Results and prospects

The cosmic diffuse X-ray background radiation has been almost completely resolved into point sources by Chandra and XMM. However, the nature and evolution of those sources are just beginning to be investigated. The answers are key to our understanding of the inter-relationship over cosmic time of (a) the formation and growth of black holes, (b) star formation, and (c) hierarchical structure formation. This requires multiwavelength followup of Chandra sources over a large area. The Chandra Multiwavelength Project (ChaMP) is a serendipitous survey of the X-ray sky, covering about 14 deg² of sky in the X-ray flux range of -13 to -16 (log 0.5-2 keV flux, cgs) and will include about 8000 sources, 70% of which are expected to be active galactic nuclei (AGN). Using Chandra archival data, we span flux limits between those reached by previous satellites and those of the deepest small-area Chandra and XMM surveys, allowing study of larger samples of rare objects like luminous absorbed AGN, groups and clusters of galaxies, and their spatial correlations. Optical imaging and spectroscopy of the ChaMP fields are underway at a variety of telescopes using Sloan g′, r′, and i′ filters to a flux limit matched to the X-ray such that about 75% of the X-ray sources will be optically identified. We also plan for radio and near-IR observations of subsets of the ChaMP sample to expand our multi-wavelength coverage and increase the fraction of sources identified.