Showing papers by "Michael W. Werner published in 1997"
TL;DR: In this article, the authors reported measurements of the [C II] fine-structure line at 157.714?m in 30 normal star-forming galaxies with the Long Wavelength Spectrometer (LWS) on the Infrared Space Observatory (ISO).
Abstract: We report measurements of the [C II] fine-structure line at 157.714 ?m in 30 normal star-forming galaxies with the Long Wavelength Spectrometer (LWS) on the Infrared Space Observatory (ISO). The ratio of the line to total far-infrared (FIR) luminosity, LC II/LFIR, measures the ratio of the cooling of gas to that of dust, and thus the efficiency of the grain photoelectric heating process. This ratio varies by more than a factor of 40 in the current sample. About two-thirds of the galaxies have LC II/LFIR ratios in the narrow range of (2-7) ? 10 -->?3. The other one-third show trends of decreasing LC II/LFIR with increasing dust temperature, as measured by the flux ratio of infrared emission at 60 and 100 ?m, F?(60 ?m)/F?(100 ?m), and with increasing star formation activity, measured by the ratio of FIR and blue-band luminosity, LFIR/L -->B. We also find three FIR-bright galaxies that are deficient in the [C II] line, which is undetected with 3 ? upper limits of LC II/LFIR ?4. The trend in the LC II/LFIR ratio with the temperature of dust and with star formation activity may be due to decreased efficiency of photoelectric heating of gas at high UV radiation intensity as dust grains become positively charged, decreasing the yield and the energy of the photoelectrons. The three galaxies with no observed photodissociation region lines have among the highest LFIR/L -->B and F?(60 ?m)/F?(100 ?m) ratios. Their lack of [C II] lines may be due to a continuing trend of decreasing LC II/LFIR with increasing star formation activity and dust temperature seen in one-third of the sample with warm IRAS colors. In that case, the upper limits on LC II/LFIR imply a ratio of UV flux to gas density of G -->0/n>10 cm -->3 (where G -->0 is in units of the local average interstellar field). The low LC II/LFIR ratio could also be due to either weak [C II], owing to self-absorption, or a strong FIR continuum from regions weak in [C II], such as dense H II regions or plasma ionized by hard radiation of active galactic nuclei. The mid-infrared and radio images of these galaxies show that most of the emission comes from a compact nucleus. CO and H I are detected in these galaxies, with H I seen in absorption toward the nucleus.
212 citations
TL;DR: In this article, the authors present new observations of the [S III] 19 μm, [O III] 52 and 88 μm and [N III] 57 μm lines toward 18 compact and ultracompact H II regions.
Abstract: We present new observations of the [S III] 19 μm, [O III] 52 and 88 μm, and [N III] 57 μm lines toward 18 compact and ultracompact (UC) H II regions. These data were combined with data from the literature and high-resolution radio continuum maps to construct detailed statistical equilibrium and ionization equilibrium models of 34 compact H II regions located at galactocentric distances (DG) 0-12 kpc. Our models simultaneously fitted the observed IR fine-structure lines and high-resolution radio continuum maps. Abundance gradients are found of the form [S/H] = (-4.45 ± 0.04) - (0.063 ± 0.006) DG (kpc), [N/H] = (-3.58 ± 0.04) - (0.072 ± 0.006) DG (kpc), and [O/H] = (-2.85 ± 0.06) - (0.064 ± 0.009) DG (kpc), and we derive Te = (4560 ± 220) + (390 ± 40) DG (kpc). The Te gradient is consistent with the Te gradient determined independently via radio recombination lines (Afflerbach et al.). We observe no dependence of S/O, N/O, or Teff on DG. Gradients in N++/O++ and O++/S++ are observed in the sense of increasing ionization with increasing DG. This is entirely consistent with the decreased line blanketing with increasing DG required by the above abundance gradients. All three gradients are best fitted by a linear dependence on DG. The abundances are consistent with production of sulfur, nitrogen, and oxygen by primary nucleosynthesis. Comparison with abundances in other galaxies implies a Hubble type between Sab and Sb for our Galaxy and an unbarred or mixed galactic structure (Vila-Costas & Edmunds). Our derived Teff is 2000-10,000 K lower than Teff expected from ZAMS stars of the same Lyman continuum flux (Panagia; Vacca et al.), probably owing to uncertainties in the UV flux of stellar models for E ≥ 35.1 eV, uncertainties in the luminosity-Teff calibration, and/or ionization of H II regions by multiple stars in some sources.
189 citations
01 Jan 1997
TL;DR: Erickson et al. as mentioned in this paper used a grating spectrometer to detect strong 63 μm emission from photodissociation regions in planetary nebulae and found that its strength correlates well with the total far-infrared power.
Abstract: Measurements of the main far-infrared cooling lines from photodissociation regions in planetary nebulae were obtained with NASA’s Kuiper Airborne Observatory, using a moderate-resolution far-infrared cooled grating spectrometer (Erickson et al. 1985). We surveyed about 20 nebulae in the [O I] 63 μm line, and detected it in most of the observed objects. We found that its strength correlates well with the total far-infrared power, with an average ratio of about 0.2%, as predicted by models of photodissociation regions (e.g. Tielens & Hollenbach 1985; Wolfire et al. 1990). Strong 63 μm emission is absent only for objects in which the ionization of the gas is just beginning and for a few evolved objects where the ionized nebula is probably matter-bounded.