Mid-infrared imaging and spectroscopy observation of the Galactic Center with Subaru/COMICS

Y. Okada1, T. Onaka1, T. Miyata2, H. Kataza4, Y. K. Okamoto5, S. Sako1,3, M. Honda1,3, T. Yamashita3, and T. Fujiyoshi3

1 Department of Astronomy, School of Science, University of Tokyo, Japan
2 Institute of Astronomy, Faculty of Science, University of Tokyo, Japan
3 Subaru Telecsope, National Astronomical Observatory of Japan, Japan
4 The Institute of Space and Astronautical Science, Japan
5 Institute of Physics, Center for Natural Science, Kitasato University, Japan

E-mail contact: okada@astron.s.u-tokyo.ac.jp, onaka@astron.s.u-tokyo.ac.jp

We report the results of mid-infrared (7.8-13.2um) high-spatial resolution imaging and spectroscopic observations of the Galactic center region with Subaru/COMICS (Cooled Mid-Infrared Camera and Spectrometer). The imaging observations were made for the area of 42 arcsec x32 arcsec around Sgr A* with the spatial resolution of about 0.3 arcsec. In the images of 8.7um, 11.7um and 12.4um bright infrared sources (IRS 1, IRS 10, IRS 7, and so on) and small structures in the diffuse emission from the northern arm and the bar are clearly seen. Other faint structures are also seen in the south-east of the Galactic center. No intensity enhancement is detected around Sgr A* at any observed wavelengths. The color map of 8.7um to 12.4um indicates that the individual infrared sources have their own heating sources in them, and that the hot cluster near Sgr A* heats the diffuse component around it. The spectroscopic observations were carried out for 7.8-13.2um with the spectral resolution of 250. The 36 arcsec-long slit goes through IRS 1 and Sgr A*, and IRS 10 and IRS 7. At all positions, the spectrum shows a clear silicate absorption feature centered at 9.7um and the [NeII] 12.8um line emission. Other forbidden lines, such as [SIV] 10.51um and [ArIII] 8.99um, and the UIR bands are not detected. We fit the spectrum by assuming a simple model of hot and cold silicate dust components and derive the temperature of the hot dust and the optical depth of the cold dust component. Around IRS 1 and IRS 10, there seems to be some extra absorption component at wavelengths shorter than 8.5um. IRS 7 and IRS 3 do not show this absorption feature. We investigate whether this is also present in the ISM dust along the line of sight. Possible carriers are also discussed. Based on the one-dimensional [NeII] 12.8um line intensity distribution, we conclude that the hot cluster near Sgr A* ionizes gases in this region.