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 inten sity of this line have been a puzzle. In this letter we present a map of th e GC in the J=1-->0 line of SiO covering the same region than the ASCA obse rvations. The SiO emission is restricted to molecular clouds with radial ve locity 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 t he 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 greater than or similar to 20 in th e regions with strong Fe 6.4 keV line. This indicates that the Fe 6.4 keV l ine mainly arises from molecular clouds with large gas phase abundance of r efractory elements. We discuss the implications of the correlation on the o rigin of the hard X-rays, and the heating and the chemistry of the molecula r clouds in the GC.