A correlation between the SiO and the Fe 6 . 4 keV line emission from the Galactic center

One of the most interesting results of the X-ray observations with the ASCA satellite of the Galactic center (GC) is the spatial distribution and the intensity of the Fe line at 6.4 keV. Up to now the morphology and the intensity of this line have been a puzzle. In this letter we present a map of the GC in the J=1→0 line of SiO covering the same region than the ASCA observations. The SiO emission is restricted to molecular clouds with radial velocity between 10 and 60 km s −1 in the Sgr A and Sgr B complexes. We find a correlation between the SiO morphology and the spatial distribution of the Fe 6.4 keV line, on the large scale and also within Sgr A and Sgr B. The SiO abundance increases by a factor of > ∼20 in the regions with strong Fe 6.4 keV line. This indicates that the Fe 6.4 keV line mainly arises from molecular clouds with large gas phase abundance of refractory elements. We discuss the implications of the correlation on the origin of the hard X-rays, and the heating and the chemistry of the molecular clouds in the GC.