Interferometric observations of FeO towards Sagittarius B2

We have used the Nobeyama Millimeter Array (NMA) to carry out aperture synthesis observations of the J=5-4 ground state rotational transition of FeO molecule at 153.135273 GHz towards the galactic center HII region Sagittarius B2 Main (Sgr B2 M). We confirm the detection of this line in absorption with the IRAM 30-m telescope by Walmsley et al. (2002). Due to the higher angular resolution ( 6”.5 * 3”.0) of our NMA observations, we were able to show that the absorption has a broader line width and a deeper apparent optical depth toward the central 9”.2 * 8*.0 area around the ultra-compact (UC) HII regions. This suggests a higher column density of FeO towards the UCHII regions associated with Sgr B2 M than along adjacent lines of sight sampled with the IRAM 30-m telescope. Our results will be a crucial step toward understanding not only the chemistry of iron-bearing species in the interstellar medium, but also the degree of depletion of heavy elements.