ISO LWS far-infrared line and continuum fluxes for a sample of 227 galaxies selected from the ISO Data Archive spanning an IRAS 60 µm / 100 µm color range of 0.2-1.4 and 60 µm flux densities between 0.1 Jy and 1300 Jy are presented. The far-infrared lines detected in this sample include the seven fine structure lines ([C II] 158 µm, [O I] 145 µm, [N II] 122 µm, [O III] 88 µm, [O I] 63 µm, [N III] 57 µm, [O III] 52 µm) and multiple OH (53 µm, 65 µm, 79 µm, 84 µm, 119 µm, 163 µm) and H2O (59 µm, 67 µm, 75 µm, 101 µm, 108 µm) transitions. An unidentified line at 74.24 µm previously reported in NGC 7027 is detected in NGC 1068. Serendipitous detections of Milky Way [C II] 158 µm are also observed in twelve sky positions. This sample is the largest collection of far-infrared line observations ever assembled and includes 465 independent LWS observations yielding some 1300 line fluxes, 600 line flux upper limits, and 800 continuum fluxes.
The data presented here can be separated into two subsets, one where the source is resolved and one where it is unresolved by the 75" LWS beam. The resolved subset contains 46 galaxies and the unresolved subset contains 181 galaxies. The statistical trends in the unresolved subset are examined, and the following results are compared to earlier studies (Malhotra et al. 1997, 2001; Leech et al. 1999; Luhman et al. 1998, 2003; Negishi et al. 2001):
1. The LWS continuum agrees with fluxes predicted from IRAS data and the spectral energy distribution models of Dale & Helou (2002) to within 25% at 52 µm, 57 µm, 63 µm, 88 µm, 122 µm, 145 µm, 158 µm, and 170 µm.
2. The [C II] 158 µm/FIR ratio peaks for normal, star-forming galaxies with 60 µm / 100 µm ratios of 0.3-0.6 and FIR/B ratios of 0.1-1. The [C II]/FIR ratio in quiescent galaxies with 60 µm / 100 µm ratios less than 0.3 and FIR/B ratios less than 0.1 is consistent with normal, star-forming galaxies. The [C II] 158 µm/FIR ratio decreases with increasing dust temperatures (60 µm / 100 µm > 0.6) and infrared to blue ratio (FIR/B > 1).
3. The [O I] 63 µm/FIR ratio shows no obvious correlation with 60 µm / 100 µm and a decrease as a function of FIR/B.
4. The ratio [N II] 122 µm/FIR shows a similar correlation as [C II] 158 µm/FIR, decreasing as the 60 µm / 100 µm and FIR/B ratios increase. The [N II] 122 µm / [C II] 158 µm shows no correlation with either the 60 µm / 100 µm or FIR/B ratio, indicating that a large fraction of [C II] 158 µm may arise from H2 regions.
5. In contrast to [C II] 158 µm/FIR and [N II] 122 µm/FIR), the [O III] 88 µm/FIR ratio increases as the 60 µm / 100 µm ratio increases. This increase might be due to the higher density of H2 regions found in galaxies with warmer far-infrared colors. The [O III] 88 µm/FIR ratio, however, decreases with increasing FIR/B ratio.
6. The [O I] 63 µm/[C II] 158 µm ratio increases as the 60 µm / 100 µm ratio increases, but shows no correlation with FIR/B. In warmer galaxies (60 µm / 100 µm > 0.8), [O I] 63 µm becomes more important than [C II] 158 µm in cooling the interstellar medium.
7. The ([O I] 63 µm + [C II] 158 µm)/FIR ratio is a measure of the gas heating efficiency in PDRs, and shows only a slight decrease with increasing 60 µm / 100 µm ratio for spirals but no decrease for the unresolved galaxies as a whole. The ([O I] 63 µm + [C II] 158 µm)/FIR ratio does, however, decrease with increasing FIR/B ratio for the unresolved subset of galaxies as a whole.
8. The [O III] 88 µm / [C II] 158 µm ratio increases with increasing 60 µm / 100 µm ratio. This is due to the dramatic falloff of [C II] 158 µm emission in galaxies showing warmer far-infrared emission. The [O III] 88 µm / [C II] 158 µm ratio decreases with increasing FIR/B ratio.
9. The [O III] 88 µm / [O I] 63 µm ratio has no correlation with the 60 µm / 100 µm ratio. The [O III] 88 µm / [O I] 63 µm ratio decreases slightly with increasing FIR/B.
These data provide a framework through which the interstellar medium of these galaxies may be studied in the future.
We thank several people for their contributions: Harold Corwin for reclassifying the galaxies in this sample according to the RC3 catalog; Steve Lord, Tom Jarrett, and Alessandra Contursi for helpful discussions; Heather Maynard for her suggestions and support; Pat Patterson and Niles McElveney for assistance with the preparation of the manuscript; and an anonymous referee for many helpful suggestions. The data for this project are based on observations with the Infrared Space Observatory, an ESA project with instruments funded by ESA member states (especially the PI countries: France, Germany, the Netherlands, and the United Kingdom) with the participation of ISAS and NASA. The ISO Spectral Analysis Package (ISAP) is a joint development by the LWS and SWS Instrument Teams and Data Centers. Contributing institutes are CESR, IAS, IPAC, MPE, RAL, and SRON. This research has made use of the NASA/IPAC Extragalactic Database that is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA). This work has made use of data services of the InfraRed Science Archive (IRSA) at the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration (NASA).