5 Summary

We have investigated the LWS spectra of 43-197 $\mu$m for 34 nearby galaxies. In addition to the detected emission line intensities, we estimated the far-infrared intensity from submicron grains from the continuum emission of $\ge$80 $\mu$m and derived the average dust temperature. We obtained the following results.

1.

We have found that the ratios of [C II]158 $\mu$m and [N II]122 $\mu$m flux to the total far-infrared flux FIR decrease as the far-infrared color R(60/100) becomes bluer, but the ratio of [O I]63 $\mu$m to FIR does not show a systematic trend with the color. The ratio of [O III]88 $\mu$m to FIR shows a large scatter with a weak trend of increase with the color. These are similar to those obtained for the normal galaxy sample by Malhotra et al. (2001b).

2.

There is no clear difference seen between AGNs and starburst galaxies in the present sample in these trends, suggesting that even in AGNs the far-infrared properties are dominated by star-formation activities.

3.

Based on the comparison with the PDR model by Kaufman et al. (1999), we found that the typical neutral gas density in galaxies increases linearly with the radiation field intensity.

4.

About a half of the observed [C II]158 $\mu$m emission is estimated to come from PDRs. The rest can be attributed to that coming from the diffuse ionized gas that emits the [N II]122 $\mu$m line.

5.

The observed decrease in [C II]158 $\mu$m $/{\it FIR}$ with the FIR color can be interpreted in terms of either the increase in the collisional de-excitation in the [C II] transition at high density or the decrease in the ionized component. Decrease in the photoelectric yield due to the charge up of dust grains does not seem to play a primary role in the observed trend.

6.

We summarize the relations among the far-infrared properties for the present sample galaxies. These are thought to indicate the general characteristics for a wide range of galaxies, including starburst, AGNs, and normal galaxies and can be used as a measure in the investigation of activities in distant galaxies in future observations.

Acknowledgements

The authors thank all the members of Japanese ISO group, particularly H. Okuda, K. Kawara, and Y. Satoh for their continuous help and encouragement and Y. Okada for her help in the calculation of the line ratios. K.W.C. was supported by the JSPS Postdoctoral Fellowship for Foreign Researchers. This work was supported in part by Grant-in-Aids for Scientific Research from the JSPS.