Properties of dust at the Galactic center probed by AKARI far-infrared spectral mapping
Detection of a dust feature
H. Kaneda1, A. Yasuda1,2, T. Onaka3, M. Kawada2, N. Murakami6, T. Nakagawa2, Y. Okada4 and H. Takahashi5
1 Graduate School of Science, Nagoya University, Chikusa-ku, 464-8602, Nagoya, Japan
2 Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, 252-5210 Kanagawa, Japan
3 Department of Astronomy, Graduate School of Science, University of Tokyo, Bunkyo-ku, 113-0033 Tokyo, Japan
4 I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
5 Institute of Astronomy, Graduate School of Science, University of Tokyo, Mitaka, 181-0015 Tokyo, Japan
6 Bisei Astronomical Observatory, Ibara, 714-1411 Okayama, Japan
Received: 17 March 2012
Accepted: 12 May 2012
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.
Key words: dust, extinction / ISM: clouds / Galaxy: center / infrared: ISM
© ESO, 2012