Properties of dust at the Galactic center probed by AKARI far-infrared spectral mapping. Detection of a dust feature

Abstract

Aims: We investigate the properties of interstellar dust in the Galactic center region toward the Arches and Quintuplet clusters.
Methods: With the Fourier Transform Spectrometer of the AKARI/Far-Infrared Surveyor, we performed the far-infrared (60-140 cm^-1) spectral mapping of an area of about 10' × 10' that includes both clusters to obtain a low-resolution (R = 1.2 cm^-1) spectrum at every spatial bin of 30'' × 30''.
Results: We derive the spatial variations in the dust continuum emission at different wavenumbers, which are compared with those of the [OIII] 88 μm (113 cm^-1) emission and the OH 119 μm (84 cm^-1) absorption. The spectral fitting shows that two modified blackbody components with temperatures of ~20 K and ~50 K 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 80-90 cm^-1 (110-130 μm).
Conclusions: 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.