Point-source Contribution to the Diffuse X-Ray Background below 1 keV and Its Effect on Our Understanding of the Circumgalactic Medium

We studied the spectral signature of different components of the diffuse X-ray background (DXB), including Local Hot Bubble, solar wind charge exchange, galactic halo, and typically unresolved point sources (galaxies and active galactic nuclei), in the direction of the Chandra Deep Field South using the 4 Ms XMM-Newton survey and Chandra 4 Ms Source Catalog. In this paper, we present our results showing how the different components contribute to the DXB below 1 keV. In particular, we have found that ∼6% of the emission at $\tfrac{3}{4}$ keV (all-sky average value ≈3 × 10 ^−3 cm ^−6 pc), which is typically associated with galactic halo (GH) and circumgalactic medium (CGM), is, in fact, due to emission from typically unresolved galaxies. We will discuss the effect that this has on our understanding of GH and CGM and to our understanding of the missing CGM baryons.