the contamination results for the Cep B and ONC $Chandra$ fields to substantially different X-ray observations.

The purpose of this study is to present our contaminant simulation method and its application to the $Chandra$ Carina Complex Project [CCCP; @Townsley11a]. The simulation methods are refined from those described by @Getman06. The Carina Nebula (NGC 3372) is one of the richest nearby high-mass star-forming complexes, located $2.3$ kpc from the Sun towards the Galactic direction $(l,b)=(287^{\circ}.6, -0^{\circ}.8)$ [@Smith08]. The CCCP combines 22 spatially contiguous $Chandra$-ACIS-I pointings with nominal exposure of $60$ ksec covering $1.42$ square degrees around the chain of famous massive star-forming regions in Carina [@Townsley11a]. A relatively shallow molecular cloud [@Yonekura05] covers roughly 1/3 of the CCCP field (Figure \[fig\_spatial\]c). More than $14000$ CCCP point sources have been detected [@Broos11a].

The simulations of Galactic stellar and extragalactic contaminating populations in CCCP are described in §\[contaminants\_main\_section\]. They show that $\sim5000$ contaminating sources are expected in the CCCP catalog. Basic properties of these simulated contaminating sources (spatial distribution, X-ray median energies, and $J$-band magnitudes) are presented in §\[contamination\_properties\_section\]. The comparison of the properties of the simulated contaminating sources and the real CCCP sources is considered, at a simplistic level, in §\[qualitative\_analysis\_section\]. Based 