We have collected dozens of mid-infrared spectra showing UIR bands from diffuse Galactic emitting regions with the AKARI's Infrared Camera (IRC) onboard AKARI, as part of the ISMGN Mission Program. The datasets cover various directions in the inner Galactic Plane ( |l| < 70 deg), in the outer Galactic Plane ( |l| > 70 deg), and in the off-Plane ( |b| > 2 deg). The variations in the UIR band ratios are examined in terms of the radiation environments judged from the far-infrared ( 50 − 170 μm ) spectral energy distribution (SED) made with AKARI/FIS All Sky Survey data at each slit position where mid-IR spectra were obtained. We have found that the band ratios of 6.2 μm / 11.2 μm and 7.7 μm / 11.2 μm toward the inner Galaxy are systematically higher than those toward the outer Galaxy and off the Galactic plane. Likely causes of the variations in properties of UIR bands in diffuse emission on a Galactic scale are discussed in this paper.

ABSTRACT
1. INTRODUCTION
2. OBSERVATION
3. Galactic-Scale Variations of UIR Bands
REFERENCES

• I. SAKON(Department of Astronomy, Graduate School of Science, University of Tokyo)
• T. ONAKA(Department of Astronomy, Graduate School of Science, University of Tokyo)
• T. I. MORI(Department of Astronomy, Graduate School of Science, University of Tokyo)
• R. OHSAWA(Department of Astronomy, Graduate School of Science, University of Tokyo)
• Y. DOI(Department of Earth Science and Astronomy, Graduate School of Arts and Sciences, University of Tokyo)
• Y. OKADA(Universitat zu Koln, I. Physikalisches Institut)
• H. KANEDA(Graduate School of Science, Nagoya University)
• T. OOTSUBO(Astronomical Institute, Graduate School of Science, Tohoku University)