Far-Infrared [C II] Line Survey Observations of the Galactic Plane

Takao Nakagawa, Yukari Yamashita Yui, Yasuo Doi, Haruyuki Okuda,
Hiroshi Shibai, and Kenji Mochizuki
(The Institute of Space and Astronautical Science,
Yoshinodai 3-1-1, Sagamihara, Kanagawa 229, Japan)
Tetsuo Nishimura\altaffilmark and Frank J. Low
(Steward Observatory, University of Arizona, Tucson, AZ 85721)

To be published in the ApJ Suppl. Apr. 1998 Issue

abstract

We present results of our survey observations of the [C II] 158 micron line emission from the Galactic plane using the Balloon-borne Infrared Carbon Explorer (BICE). Our survey covers a wide area (350 deg < l < 25 deg, |b| < 3 deg) with a spatial resolution of 15'. We employed a new observing method called the ``fast spectral scanning'' to make large-scale observations efficiently.

Strong [C II] line emission was detected from almost all areas we observed. In the general Galactic plane, the spatial distribution of the [C II] line emission correlates very well with that of far-infrared continuum emission, but diffuse components are more prominent in the [C II] line emission; the I_[CII]/I_FIR ratio is ~0.6 % for diffuse components but is ~0.2 % for compact sources such as active star-forming regions. In the Galactic center region, on the other hand, the distribution of the [C II] line emission is quite different from that of the far-infrared continuum emission, and the I_[CII]/I_FIR ratio is systematically lower there.

The FWHM velocity resolution of our instrument is 175 km/s, but we determined the central velocity of the line at each observed point very precisely with statistical errors as small as +- 6 km/s. The longitudinal distribution of the central velocity clearly shows the differential rotation pattern of the Galactic disk and also violent velocity fields around the Galactic center.

keywords{Galaxy: General -- infrared: interstellar: lines -- ISM: Clouds}

nakagawa@koala.astro.isas.ac.jp