〔CII〕Continuum Intensity Ratio in the Far-Infrared Toward the Central Kiloparsec of the Nearby Spiral Galaxy M31

We observed the nearby galaxy M31 in the 〔C II〕158 μm emission line.An ex tended component was detected over the cent ral 1.5 kpc region with a line-to-continuum ratio of(CII)/40-12μm≈6×10^-3.This ratio is 3 times larger than that of the Galactic counterpart and is comparable to that in the general Galactic Plane.We expect that the difference between the two central regions are due to different gas densities;the self-shielding of CO molecules decreases theC⁺ abundance at the higher density in the Galactic case.