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.