Properties of dust at the Galactic center probed by AKARI far-infrared spectral mapping

Detection of a dust feature

H. Kaneda¹, A. Yasuda^1,2, 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
e-mail: kaneda@u.phys.nagoya-u.ac.jp
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

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.