Diffuse far-infrared [] line emission from high Galactic latitude

¹ The Institute of Space and Astronautical Science (ISAS), 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510, Japan
² Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
³ Gunma Astronomical Observatory, 6860-86 Nakayama, Takayama, Agatsuma Gunma, 377-0702, Japan
⁴ Communications Reserch Laboratory, 4-2-1 Nukui-kitamachi, Koganei, Tokyo 184-8795, Japan
⁵ Kansai Advanced Research Center, Communications Research Laboratory, 588-2 Iwaoka, Nishi-ku, Kobe 651-2492, Japan
⁶ College of Arts and Sciences, University of Tokyo, Komaba 3-8-1, Meguro, Tokyo 153-8902, Japan

Corresponding author: S. Makiuti, makiuti@ir.isas.ac.jp

Received: 23 July 2001
Accepted: 30 October 2001

Abstract

The Far-Infrared Line Mapper (FILM) onboard the Infrared Telescope in Space (IRTS) made a survey for the far-infrared [] 158 μm line emission with high sensitivity and moderate spatial resolution. We have found that diffuse [] line emission extends to high Galactic latitude regions. The [] line intensity at ranges from to  . Comparisons of the distribution of the [] line emission with those of the column density and far-infrared radiation show some correlations, but the [] line emission differs from the far-IR and HI emission at high Galactic latitudes. These differences suggest that the [] line primarily comes from ionized gas in the high-latitude regions. The intensities of the [] line emission on the southern side () of the Galactic plane are systematically larger than those on the northern side (). We infer from this difference that there is a displacement of the Sun with respect to the center of interstellar medium from which the [] line comes. When an exponential distribution is assumed for the [] emitting gas, it is expected that the Sun is located at the distance of about 17% of the scale height above the center of the gas. This is consistent with the previously reported displacement of the Sun from the Galactic plane.