2012A&A...543A..79K

We investigate the properties of interstellar dust in the Galactic center region toward the Arches and Quintuplet clusters. With the Fourier Transform Spectrometer of the AKARI/Far-Infrared Surveyor, we performed the far-infrared (60-140cm^–1) spectral mapping of an area of about 10'x10' that includes both clusters to obtain a low-resolution (R=1.2cm^–1) spectrum at every spatial bin of 30''x30''. We derive the spatial variations in the dust continuum emission at different wavenumbers, which are compared with those of the [OIII] 88µm (113cm^–1) emission and the OH 119µm (84cm^–1) absorption. The spectral fitting shows that two modified blackbody components with temperatures of ∼20K and ∼50K can reproduce most of the continuum spectra. For some spectra, however, we find that there is a significant excess on top of a modified blackbody continuum around 80-90cm^–1 (110-130µm). The warmer dust component is spatially correlated with the [OIII] emission and hence likely to be associated with the highly-ionized gas locally heated by intense radiation from the two clusters. The excess emission probably represents a dust feature, which is found to be spatially correlated with the OH absorption and a CO cloud. We find that a dust model including micron-sized graphite grains can quite closely reproduce the observed spectrum with the dust feature.