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

Abstract

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. We carried out imaging spectroscopic observations of four giant Galactic star-forming regions with the Fourier Transform Spectrometer (FTS) onboard AKARI. We obtained [OIII] 88 micron and [CII] 158 micron line intensity maps of all the regions: G3.270-0.101, G333.6-0.2, NGC3603, and M17. For G3.270-0.101, we obtained high-spatial-resolution [OIII] 88 micron line-emission maps and a FIR continuum map for the first time, which imply that [OIII] 88 micron emission identifies the excitation sources more clearly than the radio continuum emission. In G333.6-0.2, we found a local [OIII] 88 micron emission peak, which is indicative of an excitation source. This is supported by the 18 micron continuum emission, which is considered to trace the hot dust distribution. For all regions, the [CII] 158 micron emission is distributed widely as suggested by previous observations of star-forming regions. We conclude that [OIII] 88 micron 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.