The C ii 158 m 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 m 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 m. 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.
We have fit the far-ultraviolet (FUV) to sub-millimeter (850 μm) spectral energy distributions (SEDs) of the 61 galaxies from the Key Insights on Nearby Galaxies: A Far-Infrared Survey with Herschel ...(KINGFISH). The fitting has been performed using three models: the Code for Investigating GALaxy Evolution (CIGALE), the GRAphite-SILicate approach (GRASIL), and the Multiwavelength Analysis of Galaxy PHYSical properties (MAGPHYS). We have analyzed the results of the three codes in terms of the SED shapes, and by comparing the derived quantities with simple “recipes” for stellar mass (Mstar), star-formation rate (SFR), dust mass (Mdust), and monochromatic luminosities. Although the algorithms rely on different assumptions for star-formation history, dust attenuation and dust reprocessing, they all well approximate the observed SEDs and are in generally good agreement for the associated quantities. However, the three codes show very different behavior in the mid-infrared regime: in the 5–10 μm region dominated by PAH emission, and also between 25 and 70 μm where there are no observational constraints for the KINGFISH sample. We find that different algorithms give discordant SFR estimates for galaxies with low specific SFR, and that the standard recipes for calculating FUV absorption overestimate the extinction compared to the SED-fitting results. Results also suggest that assuming a “standard” constant stellar mass-to-light ratio overestimates Mstar relative to the SED fitting, and we provide new SED-based formulations for estimating Mstar from WISE W1 (3.4 μm) luminosities and colors. From a principal component analysis of Mstar, SFR, Mdust, and O/H, we reproduce previous scaling relations among Mstar, SFR, and O/H, and find that Mdust can be predicted to within ∼0.3 dex using only Mstar and SFR.
The physical state of interstellar gas and dust is dependent on the processes which heat and cool this medium. To probe heating and cooling of the interstellar medium over a large range of infrared ...surface brightness, on sub-kiloparsec scales, we employ line maps of CII 158 mu m, OI 63 mu m, and NII 122 mu m in NGC 1097 and NGC 4559, obtained with the Photodetector Array Camera & Spectrometer on board Herschel. We matched new observations to existing Spitzer Infrared Spectrograph data that trace the total emission of polycyclic aromatic hydrocarbons (PAHs). We confirm at small scales in these galaxies that the canonical measure of photoelectric heating efficiency, (CII + OI)/TIR, decreases as the far-infrared (far-IR) color, nufunctionof sub(nu)(70 mu m) nufunctionof sub(nu)(100 mu m), increases. In contrast, the ratio of far-IR cooling to total PAH emission, (CII + OI)/PAH, is a near constant ~6% over a wide range of far-IR color, 0.5 < nufunctionof sub(nu)(70 mu m) nufunctionof sub(nu)(100 mu m) <, ~0.95. In the warmest regions, where nufunctionof sub(nu)(70 mu m) nufunctionof sub(nu)(100 mu m) > ~0.95, the ratio (CII + OII)/PAH drops rapidly to 4%. We derived representative values of the local ultraviolet radiation density, G sub(0), and the gas density, n sub(H), by comparing our observations to models of photodissociation regions. The ratio G sub(0)/n sub(H), derived from fine-structure lines, is found to correlate with the mean dust-weighted starlight intensity, left angle bracketUright angle bracket, derived from models of the IR spectral energy distribution. Emission from regions that exhibit a line deficit is characterized by an intense radiation field, indicating that small grains are susceptible to ionization effects. We note that there is a shift in the 7.7/11.3 mu m PAH ratio in regions that exhibit a deficit in (CII + OI)/PAH, suggesting that small grains are ionized in these environments.
We present an update to the ultraviolet-to-radio database of global broadband photometry for the 79 nearby galaxies that comprise the union of the KINGFISH (Key Insights on Nearby Galaxies: A ...Far-Infrared Survey with Herschel) and SINGS (Spitzer Infrared Nearby Galaxies Survey) samples. The 34-band data set presented here includes contributions from observational work carried out with a variety of facilities including GALEX, SDSS, Pan-STARRS1, NOAO, 2MASS, Wide-Field Infrared Survey Explorer, Spitzer, Herschel, Planck, JCMT, and the VLA. Improvements of note include recalibrations of previously published SINGS BVRCIC and KINGFISH far-infrared/submillimeter photometry. Similar to previous results in the literature, an excess of submillimeter emission above model predictions is seen primarily for low-metallicity dwarf or irregular galaxies. This 33-band photometric data set for the combined KINGFISH+SINGS sample serves as an important multiwavelength reference for the variety of galaxies observed at low redshift. A thorough analysis of the observed spectral energy distributions is carried out in a companion paper.
Physical conditions of the interstellar medium in galaxies are closely linked to the ambient radiation field and the heating of dust grains. In order to characterize dust properties in galaxies over ...a wide range of physical conditions, we present here the radial surface brightness profiles of the entire sample of 61 galaxies from Key Insights into Nearby Galaxies: Far-Infrared Survey with Herschel (KINGFISH). The main goal of our work is the characterization of the grain emissivities, dust temperatures, and interstellar radiation fields (ISRFs) responsible for heating the dust. We first fit the radial profiles with exponential functions in order to compare stellar and cool-dust disk scalelengths, as measured by 3.6 μm and 250 μm surface brightnesses. Our results show thatthe stellar and dust scalelengths are comparable, with a mean ratio of 1.04, although several galaxies show dust-to-stellar scalelength ratios of 1.5 or more. We then fit the far-infrared spectral energy distribution (SED) in each annular region with single-temperature modified blackbodies using both variable (MBBV) and fixed (MBBF) emissivity indices β, as well as with physically motivated dust models. The KINGFISH profiles are well suited to examining trends of dust temperature Tdust and β because they span a factor of ~200 in the ISRF intensity heating the bulk of the dust mass, Umin. Results from fitting the profile SEDs suggest that, on average, Tdust, dust optical depth τdust, and Umin decrease with radius. The emissivity index β also decreases with radius in some galaxies, but in others is increasing, or rising in the inner regions and falling in the outer ones. Despite the fixed grain emissivity (average β ~ 2.1) of the physically-motivated models, they are well able to accommodate flat spectral slopes with β ≲ 1. An analysis of the wavelength variations of dust emissivities in both the data and the models shows that flatter slopes (β ≲ 1.5) are associated with cooler temperatures, contrary to what would be expected from the usual Tdust – β degeneracy. This trend is related to variations in Umin since β and Umin are very closely linked over the entire range in Umin sampled by the KINGFISH galaxies: low Umin is associated with flat β ≲ 1. Both these results strongly suggest that the low apparent β values (flat slopes) in MBBV fits are caused by temperature mixing along the line of sight, rather than by intrinsic variations in grain properties. Finally, a comparison of dust models and the data show a slight ~10% excess at 500 μm for low metallicity (12 + log (O/H) ≲ 8) and low far-infrared surface brightness (Σ500).
The metal content of a galaxy, a key property for distinguishing between viable galaxy evolutionary scenarios, strongly influences many of the physical processes in the interstellar medium. An ...absolute and robust determination of extragalactic metallicities is essential in constraining models of chemical enrichment and chemical evolution. Current gas-phase abundance determinations, however, from optical fine-structure lines are uncertain to 0.8 dex as conversion of these optical line fluxes to abundances is strongly dependent on the electron temperature of the ionized gas. In contrast, the far-infrared (far-IR) emission lines can be used to derive an O super(++) abundance that is relatively insensitive to temperature, while the ratio of the optical to far-IR lines provides a consistent temperature to be used in the derivation of an O super(+) abundance. We present observations of the OIII 88 mu m fine-structure line in NGC 628 that were obtained as part of the Key Insights on Nearby Galaxies: a Far Infared Survey with Herschel program. These data are combined with optical integrated field unit data to derive oxygen abundances for seven H II regions. We find the abundance of these regions to all lie between the high and low values of strong-line calibrations and to be in agreement with estimates that assume temperature fluctuations are present in the H II regions.
Abstract
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
μ
m ...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.
We present a comprehensive study of the velocity dispersion of the atomic (H sub(I)) and molecular (H sub(2)) gas components in the disks (R lap R sub(25)) of a sample of 12 nearby spiral galaxies ...with moderate inclinations. Our analysis is based on sensitive high-resolution data from the THINGS (atomic gas) and HERACLES (molecular gas) surveys. To obtain reliable measurements of the velocity dispersion, we stack regions several kiloparsecs in size, after accounting for intrinsic velocity shifts due to galactic rotation and large-scale motions. We stack using various parameters: the galactocentric distance, star formation rate surface density, HI surface density, H sub(2) surface density, and total gas surface density. We fit single Gaussian components to the stacked spectra and measure median velocity dispersions for HI of 11.9 + or - 3.1 km s super(-1) and for CO of 12.0 + or - 3.9 km s super(-1). The CO velocity dispersions are thus, surprisingly, very similar to the corresponding ones of HI, with an average ratio of sigma sub(HI)/sigma sub(CO) = 1.0 + or - 0.2 irrespective of the stacking parameter. The measured CO velocity dispersions are significantly higher (factor of ~2) than the traditional picture of a cold molecular gas disk associated with star formation. The high dispersion implies an additional thick molecular gas disk (possibly as thick as the HI disk). Our finding is in agreement with recent sensitive measurements in individual edge-on and face-on galaxies and points toward the general existence of a thick disk of molecular gas, in addition to the well-known thin disk in nearby spiral galaxies.
We present the first search for a dark matter annual modulation signal in the Southern Hemisphere conducted with NaI(Tl) detectors, performed by the DM-Ice17 experiment. Nuclear recoils from dark ...matter interactions are expected to yield an annually modulated signal independent of location within the Earth’s hemispheres. DM-Ice17, the first step in the DM-Ice experimental program, consists of 17 kg of NaI(Tl) located at the South Pole under 2200 m.w.e. overburden of Antarctic glacial ice. Taken over 3.6 years for a total exposure of 60.8 kg yr, DM-Ice17 data are consistent with no modulation in the energy range of 4–20 keV, providing the strongest limits on weakly interacting massive particle dark matter from a direct detection experiment located in the Southern Hemisphere. The successful deployment and stable long-term operation of DM-Ice17 establishes the South Pole ice as a viable location for future dark matter searches and in particular for a high-sensitivity NaI(Tl) dark matter experiment to directly test the DAMA/LIBRA claim of the observation of dark matter.
The use of glyphosate has increased rapidly, and there is limited understanding of its environmental fate. The objective of this study was to document the occurrence of glyphosate and the ...transformation product aminomethylphosphonic acid (AMPA) in Midwestern streams and to compare their occurrence with that of more commonly measured herbicides such as acetochlor, atrazine, and metolachlor. Water samples were collected at sites on 51 streams in nine Midwestern states in 2002 during three runoff events: after the application of pre-emergence herbicides, after the application of post-emergence herbicides, and during harvest season. All samples were analyzed for glyphosate and 20 other herbicides using gas chromatography/mass spectrometry or high performance liquid chromatography/mass spectrometry. The frequency of glyphosate and AMPA detection, range of concentrations in runoff samples, and ratios of AMPA to glyphosate concentrations did not vary throughout the growing season as substantially as for other herbicides like atrazine, probably because of different seasonal use patterns. Glyphosate was detected at or above 0.1 mu g/l in 35 percent of pre-emergence, 40 percent of post-emergence, and 31 percent of harvest season samples, with a maximum concentration of 8.7 mu g/l. AMPA was detected at or above 0.1 mu g/l in 53 percent of pre-emergence, 83 percent of post-emergence, and 73 percent of harvest season samples, with a maximum concentration of 3.6 mu g/l. Glyphosate was not detected at a concentration at or above the U.S. Environmental Protection Agency's maximum contamination level (MCL) of 700 mu g/l in any sample. Atrazine was detected at or above 0.1 mu g/l in 94 percent of pre-emergence, 96 percent of post-emergence, and 57 percent of harvest season samples, with a maximum concentration of 55 mu g/l. Atrazine was detected at or above its MCL (3 mu g/l) in 57 percent of pre-emergence and 33 percent of post-emergence samples.
![The Origins of [C ii] Emiss...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0004-637X/small "The Origins of [C ii] Emission in Local Star-forming Galaxies")
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