With its relatively low ionization potential, C+ can be found throughout the interstellar medium (ISM) and provides one of the main cooling channels of the ISM via the [C ii] 157 μm emission. While the strength of the [C ii] line correlates with the star formation rate, the contributions of the various gas phases to the [C ii] emission on galactic scales are not well established. In this study we establish an empirical multi-component model of the ISM, including dense H ii regions, dense photon dissociation regions (PDRs), the warm ionized medium (WIM), low density and surfaces of molecular clouds (SfMCs), and the cold neutral medium (CNM). We test our model on ten luminous regions within the two nearby galaxies NGC 3184 and NGC 628 on angular scales of 500-600 pc. Both galaxies are part of the Herschel key program KINGFISH, and are complemented by a large set of ancillary ground- and space-based data. The five modeled phases together reproduce the observed [C ii] emission quite well, overpredicting the total flux slightly (about 45%) averaged over all regions. We find that dense PDRs are the dominating component, contributing 68% of the [C ii] flux on average, followed by the WIM and the SfMCs, with mean contributions of about half of the contribution from dense PDRs, each. CNM and dense H ii regions are only minor contributors with less than 5% each. These estimates are averaged over the selected regions, but the relative contributions of the various phases to the [C ii] flux vary significantly between these regions.@en

The [C ii] 158 μm fine-structure line is the brightest emission line observed in local star-forming galaxies. As a major coolant of the gas-phase interstellar medium, [C ii] balances the heating, including that due to far-ultraviolet photons, which heat the gas via the photoelectric effect. However, the origin of [C ii] emission remains unclear because C+ can be found in multiple phases of the interstellar medium. Here we measure the fractions of [C ii] emission originating in the ionized and neutral gas phases of a sample of nearby galaxies. We use the [N ii] 205 μm fine-structure line to trace the ionized medium, thereby eliminating the strong density dependence that exists in the ratio of [C ii]/[N ii] 122 μm. Using the FIR [C ii] and [N ii] emission detected by the KINGFISH (Key Insights on Nearby Galaxies: a Far- Infrared Survey with Herschel) and Beyond the Peak Herschel programs, we show that 60%-80% of [C ii] emission originates from neutral gas. We find that the fraction of [C ii] originating in the neutral medium has a weak dependence on dust temperature and the surface density of star formation, and has a stronger dependence on the gas-phase metallicity. In metal-rich environments, the relatively cooler ionized gas makes substantially larger contributions to total [C ii] emission than at low abundance, contrary to prior expectations. Approximate calibrations of this metallicity trend are provided.@en

The [NII] 122 and 205 um transitions are powerful tracers of the ionized gas in the ISM: (1) the [NII] 122/205 line ratio can be used to measure the electron density of the low-excitation, ionized gas, and (2) the intensity of these lines is directly related to the flux of ionizing photons, probing the most recent star formation activity. The study of these applications in nearby galaxies is specially relevant now that ALMA can observe both [NII] transitions at z>2. In this talk I will present Herschel observations of these pair of [NII] far-infrared lines in 21 nearby galaxies selected from the KINGFISH and Beyond the Peak samples. I will discuss the reliability of the [NII] lines as star formation tracers, and how the electron density of the ionized gas is related to other relevant ISM properties (e.g., radiation field strength, star formation activity, dust temperature, etc). @en

We present [C ii] 158 μm measurements from over 15,000 resolved regions within 54 nearby galaxies of the Kingfish program to investigate the so-called [C ii] "line-cooling deficit" long known to occur in galaxies with different luminosities. The [C ii]/TIR ratio ranges from above 1% to below 0.1% in the sample, with a mean value of 0.48 ± 0.21%. We find that the surface density of 24 μm emission dominates this trend, with [C ii]/TIR dropping as vIv (24 μm)increases. Deviations from this overall decline are correlated with changes in the gas-phase metal abundance, with higher metallicity associated with deeper deficits at a fixed surface brightness. We supplement the local sample with resolved [C ii] measurements from nearby luminous infrared galaxies and high-redshift sources from z = 1.8-6.4, and find that star formation rate density drives a continuous trend of deepening [C ii] deficit across six orders of magnitude in ΣSFR. The tightness of this correlation suggests that an approximate can be estimated directly from global measurements of [C ii]/TIR, and a relation is provided to do so. Several low-luminosity active galactic nucleus (AGN) hosts in the sample show additional and significant central suppression of [C ii]/TIR, but these deficit enhancements occur not in those AGNs with the highest X-ray luminosities, but instead those with the highest central starlight intensities. Taken together, these results demonstrate that the [C ii] line-cooling line deficit in galaxies likely arises from local physical phenomena in interstellar gas.@en

We present calibrations for star formation rate (SFR) indicators in the ultraviolet, mid-infrared, and radiocontinuumbands, including one of the first direct calibrations of 150 MHz as an SFR indicator. Our calibrationsutilize 66 nearby star-forming galaxies with Balmer-decrement-corrected Hα luminosities, which span five ordersof magnitude in SFR and have absolute magnitudes of -24 < Mr < -12. Most of our photometry andspectrophotometry are measured from the same region of each galaxy, and our spectrophotometry has beenvalidated with SDSS photometry, so our random and systematic errors are small relative to the intrinsic scatter seenin SFR indicator calibrations. We find that the Wide-field Infrared Space Explorer W4 (22.8 μm), Spitzer 24 μm,and 1.4 GHz bands have tight correlations with the Balmer-decrement-corrected Hα luminosity, with a scatter ofonly 0.2 dex. Our calibrations are comparable to those from the prior literature for L∗ galaxies, but for dwarfgalaxies, our calibrations can give SFRs that are far greater than those derived from most previous literature.@en

Our parent sample is star-forming galaxies with optical drift-scan spectrophotometry from Moustakas & Kennicutt (2006, J/ApJS/164/81) and Moustakas+ (2010, J/ApJS/190/233) that also have Sloan Digital Sky Survey III optical imaging (SDSS-III; Aihara+ 2011ApJS..193...29A). All of the galaxies in the sample have imaging at ultraviolet, optical, near-infrared, and mid-infrared wavelengths, taken from GALEX, the Swift UV/Optical Monitor Telescope, the Sloan Digital Sky Survey III (SDSS-III), the Two Micron All Sky Survey (2MASS), the Spitzer Space Telescope, and/or the Wide-field Infrared Space Explorer (WISE). Radio-continuum flux densities at 1.4GHz and 150MHz were determined using multiple sets of archival data. Our principal source of 1.4GHz flux densities is the NRAO VLA Sky Survey (NVSS, Condon+, 1998, VIII/65). Our principal source of 150MHz flux densities is the TIFR GMRT Sky Survey (TGSS), which has an angular resolution of ~25". We used the first alternative data release of the TGSS (TGSS ADR1; Intema+ 2017, J/A+A/598/A78). (1 data file).@en

Our parent sample is star-forming galaxies with optical drift-scan spectrophotometry from Moustakas & Kennicutt (2006, J/ApJS/164/81) and Moustakas+ (2010, J/ApJS/190/233) that also have Sloan Digital Sky Survey III optical imaging (SDSS-III; Aihara+ 2011ApJS..193...29A). All of the galaxies in the sample have imaging at ultraviolet, optical, near-infrared, and mid-infrared wavelengths, taken from GALEX, the Swift UV/Optical Monitor Telescope, the Sloan Digital Sky Survey III (SDSS-III), the Two Micron All Sky Survey (2MASS), the Spitzer Space Telescope, and/or the Wide-field Infrared Space Explorer (WISE). Radio-continuum flux densities at 1.4GHz and 150MHz were determined using multiple sets of archival data. Our principal source of 1.4GHz flux densities is the NRAO VLA Sky Survey (NVSS, Condon+, 1998, VIII/65). Our principal source of 150MHz flux densities is the TIFR GMRT Sky Survey (TGSS), which has an angular resolution of ~25". We used the first alternative data release of the TGSS (TGSS ADR1; Intema+ 2017, J/A+A/598/A78). (1 data file).@en