Bret Lehmer (JHU/GSFC)

X-ray Number Counts in the 4 Ms Chandra Deep Field-South: Characterizing New X-ray Source Populations

Through a large investment of director's discretionary time, the Chandra Deep Field-South (CDF-S) now has a total ACIS-I exposure reaching ~4 Ms in depth, making the CDF-S the deepest X-ray observation of the extragalactic Universe ever undertaken.  In this talk, I will present the latest estimates of the extragalactic X-ray source number counts, emphasizing the nature of the sources that contribute at the faintest flux levels.  We find that the majority of the 740 X-ray detected sources in the 4 Ms CDF-S are active galactic nuclei (AGNs); however, we estimate that normal galaxies, shining primarily by emission from X-ray binaries and hot gas, contribute ~40% of the total number counts above 0.5-2 keV fluxes of 10-17 ergs/cm2/s.  I will present a detailed break-down of the X-ray number count contributions based on a variety of source properties (e.g., AGN intrinsic column density and galaxy optical morphology) and discuss their implications for semi-analytic models that attempt to parameterize the SMBH accretion history and X-ray binary evolution in the Universe.