Optical spectroscopic followup of serendipitous Chandra sources: the Chandra Multiwavelength Project (ChaMP)

A primary goal of the Chandra Multiwavelength Project (ChaMP) is to investigate the evolution of Active Galactic Nuclei (AGN) and quasars by measuring the luminosity function out to z ≥ 4 including obscured AGN that have been missed by previous surveys. To do so, we are acquiring spectra of optical counterparts to serendipitious X‐ray sources detected by Chandra for classification and redshift determination. We have amassed about 200 spectra using the FLWO 1.5m, WIYN 3.5m, CTIO/4m, Magellan and the MMT 6.5m. We have classified the majority of optical counterparts as 65% broad line AGN, 14% narrow emission line galaxies and 12% absorption line galaxies. The remaining counterparts are either stars (8%) or galaxy clusters (1%). We have acquired a sample of 120 AGN in 12 Chandra fields.With a limiting magnitude of r ′ = 22 for spectroscopic followup, we are able to detect quasars out to z ∼ 5 and galaxies out to z ∼ 0.7. This preliminary sample forms the foundation for our measurement of the X‐ray luminosity function of AGNs out to z ∼ 4.