X‐rays from the HII Regions and Molecular Clouds near the Galactic Center

We report measurements by Chandra of a variety of X‐ray sources in the molecular clouds and HII regions of the Sgr B2, Arches, Quintuplet and the Galactic center clusters. Moderately bright X‐ray sources are present in the Sgr B2, Quintuplet and the Galactic center clusters at the positions of ultra compact HII regions and bright infrared sources. Their X‐ray spectra are fitted with models of a thin thermal plasma with 2–10 keV temperatures and luminosities of ∼10 32–33 erg s −1 . The X‐ray properties are typical of those of high‐mass young stellar objects or clusters of such objects. The Arches Cluster has three bright X‐ray sources, at the positions of bright IR and radio stars, with X‐ray luminosities of a few ×10 33 erg s −1 each, which may indicate an unusual X‐ray emission mechanism from high mass YSOs. A unique X‐ray feature of molecular clouds and HII regions near the Galactic center is the presence of diffuse emission with a strong 6.4 keV line; in Sgr B2 this is attributable to the fluorescence of gas irradiated by external sources in the Galactic center, while the diffuse emission from Arches is puzzling.