Properties of active galactic star-forming regions probed by imaging spectroscopy with the Fourier transform spectrometer (FTS) onboard AKARI

¹ I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany e-mail: okada@ph1.uni-koeln.de
² Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Kanagawa 229-8510, Japan
³ Division of Particle and Astrophysical Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
⁴ Bisei Astronomical Observatory, 1723-70 Ookura, Bisei-cho, Ibara, Okayama 714-1411, Japan
⁵ Astronomical Institute, Graduate School of Science, Tohoku University, Aramaki, Aoba-ku, Sendai 980-8578, Japan
⁶ Gunma Astronomical Observatory, 6860-86 Nakayama, Takayama, Agatsuma, Gunma 377-0702, Japan
⁷ Department of Astronomy, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

Received: 14 May 2009
Accepted: 13 October 2009

Abstract

Aims. We investigate the structure of the interstellar medium (ISM) and identify the location of possible embedded excitation sources from far-infrared (FIR) line and mid-infrared continuum emission maps.

Methods. We carried out imaging spectroscopic observations of four giant Galactic star-forming regions with the Fourier transform spectrometer (FTS) onboard AKARI. We obtained [O III] 88 μm and [C II] 158 μm line intensity maps of all the regions: G3.270-0.101, G333.6-0.2, NGC 3603, and M 17.

Results. For G3.270-0.101, we obtained high-spatial-resolution [O III] 88 μm line-emission maps and a FIR continuum map for the first time, which imply that [O III] 88 μm emission identifies the excitation sources more clearly than the radio continuum emission. In G333.6-0.2, we found a local [O III] 88 μm emission peak, which is indicative of an excitation source. This is supported by the 18 μm continuum emission, which is considered to trace the hot dust distribution. For all regions, the [C II] 158 μm emission is distributed widely as suggested by previous observations of star-forming regions.

Conclusions. We conclude that [O III] 88 μm emission traces the excitation sources more accurately than the radio continuum emission, especially where there is a high density and/or column density gradient. The FIR spectroscopy provides a promising means of understanding the nature of star-forming regions.