2018ApJ...861...94H

We use the Herschel/PACS spectrometer to study the global and spatially resolved far-infrared (FIR) fine-structure line emission in a sample of 52 galaxies that constitute the SHINING survey. These galaxies include star-forming, active-galactic nuclei (AGNs), and luminous infrared galaxies (LIRGs). We find an increasing number of galaxies (and kiloparsec-size regions within galaxies) with low line-to-FIR continuum ratios as a function of increasing FIR luminosity (L_FIR), dust infrared color, L_FIR to molecular gas mass ratio (L_FIR/M_mol), and FIR surface brightness (Σ_FIR). The correlations between the [C II]/FIR or [O I]/FIR ratios with Σ_FIR are remarkably tight (∼0.3 dex scatter over almost four orders of magnitude in Σ_FIR). We observe that galaxies with L_FIR/M_mol≳80L_☉M_☉^–1 and Σ_FIR >= 10¹¹ L_☉ kpc^–2 tend to have weak fine-structure line-to-FIR continuum ratios, and that LIRGs with infrared sizes >=1 kpc have line-to-FIR ratios comparable to those observed in typical star-forming galaxies. We analyze the physical mechanisms driving these trends in Paper II. The combined analysis of the [C II], [N II] 122 µm, and [O III] 88 µm lines reveals that the fraction of the [C II] line emission that arises from neutral gas increases from 60% to 90% in the most active star-forming regions and that the emission originating in the ionized gas is associated with low-ionization, diffuse gas rather than with dense gas in H II regions. Finally, we report the global and spatially resolved line fluxes of the SHINING galaxies to enable the comparison and planning of future local and high-z studies.