ISO spectroscopy of compact HII regions in the Galaxy - II. Ionization and elemental abundances
TL;DR: In this paper, the authors presented a rst analysis of the hydrogen recombination and atomic ne-structure lines originated in the ionized gas and derived an extinction in the K band between 0 and 3 mag.
Abstract: Based on the ISO spectral catalogue of compact H ii regions by Peeters et al. (2002), we present a rst analysis of the hydrogen recombination and atomic ne-structure lines originated in the ionized gas. The sample consists of 34 H ii regions located at galactocentric distances between RGal = 0 and 15 kpc. The SWS H i recombination lines between 2 and 8 m are used to estimate the extinction law at these wavelengths for 14 H ii regions. An extinction in the K band between 0 and 3 mag has been derived. The ne-structure lines of N, O, Ne, S and Ar are detected in most of the sources. Most of these elements are observed in two dierent ionization stages probing a range in ionization potential up to 41 eV. The ISO data, by itself or combined with radio data taken from the literature, is used to derive the elemental abundances relative to hydrogen. The present data thus allow us to describe for each source its elemental abundance, its state of ionization and to constrain the properties of the ionizing star(s). The main results of this study are as follows. The ionization ratios Ar ++ /Ar + ,N ++ /N + ,S +3 /S ++ and Ne ++ /Ne + , which measure the degree of ionization and to rst order, the hardness of the stellar radiation, seem to increase with RGal. These ionization ratios correlate well with each other, implying that the spectral hardening aects equally the full range of ionizing energies. A Galactocentric gradient of N/O (log N= O= 0:056 0:009 dex kpc 1 ) is observed in the sense of a decreasing abundance ratio with RGal in agreement with previous studies. Abundance gradients for neon and argon are derived of the form log Ne= H= 0:039 0:007 dex kpc 1 and log Ar= H= 0:045 0:011 dex kpc 1 . These elemental gradients could be enlarged by the existing Galactic Te gradient. Adopting a Te gradient of approximately 330 K kpc 1 , the slopes in the Ne/H and Ar/H gradients become 0:06 and 0:07 dex kpc 1 , respectively. Lower limits for
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TL;DR: In this paper, a study of gas-phase element abundances reported in the literature for 17 different elements sampled over 243 sight lines in the local part of our Galaxy reveals that the depletions into solid form (dust grains) are extremely well characterized by trends that employ only three kinds of parameters: an index that describes the overall level of depletion applicable to the gas in any particular sight line, and linear coefficients that describe how to derive each element's depletion from this sight-line parameter.
Abstract: A study of gas-phase element abundances reported in the literature for 17 different elements sampled over 243 sight lines in the local part of our Galaxy reveals that the depletions into solid form (dust grains) are extremely well characterized by trends that employ only three kinds of parameters. One is an index that describes the overall level of depletion applicable to the gas in any particular sight line, and the other two represent linear coefficients that describe how to derive each element's depletion from this sight-line parameter. The information from this study reveals the relative proportions of different elements that are incorporated into dust at different stages of grain growth. An extremely simple scheme is proposed for deriving the dust contents and metallicities of absorption-line systems that are seen in the spectra of distant quasars or the optical afterglows of gamma-ray bursts. Contrary to presently accepted thinking, the elements sulfur and krypton appear to show measurable changes in their depletions as the general levels of depletions of other elements increase, although more data are needed to ascertain whether or not these findings are truly compelling. Nitrogen appears to show no such increase. The incorporation of oxygen into solid form in the densest gas regions far exceeds the amounts that can take the form of silicates or metallic oxides; this conclusion is based on differential measurements of depletion and thus is unaffected by uncertainties in the solar abundance reference scale.
755 citations
TL;DR: In this article, an intermediate-resolution optical spectrophotometry of 65 galaxies obtained in support of the Spitzer Infrared Nearby Galaxies Survey (SINGS) is presented.
Abstract: We present intermediate-resolution optical spectrophotometry of 65 galaxies obtained in support of the Spitzer Infrared Nearby Galaxies Survey (SINGS). For each galaxy we obtain a nuclear, circumnuclear, and semi-integrated optical spectrum designed to coincide spatially with mid- and far-infrared spectroscopy from the Spitzer Space Telescope. We make the reduced, spectrophotometrically calibrated one-dimensional spectra, as well as measurements of the fluxes and equivalent widths of the strong nebular emission lines, publically available. We use optical emission-line ratios measured on all three spatial scales to classify the sample into star-forming, active galactic nuclei (AGNs), and galaxies with a mixture of star formation and nuclear activity. We find that the relative fraction of the sample classified as star forming versus AGN is a strong function of the integrated light enclosed by the spectroscopic aperture. We supplement our observations with a large database of nebular emission-line measurements of individual H II regions in the SINGS galaxies culled from the literature. We use these ancillary data to conduct a detailed analysis of the radial abundance gradients and average H II-region abundances of a large fraction of the sample. We combine these results with our new integrated spectra to estimate the central and characteristic (globally averaged) gas-phase oxygen abundances of all 75 SINGS galaxies. We conclude with an in-depth discussion of the absolute uncertainty in the nebular oxygen abundance scale.
624 citations
TL;DR: In this article, a study of gas-phase element abundances reported in the literature for 17 different elements sampled over 243 sight lines in the local part of our Galaxy reveals that the depletions into solid form (dust grains) are extremely well characterized by trends that employ only three kinds of parameters: an index that describes the overall level of depletion applicable to the gas in any particular sight line, and linear coefficients that describe how to derive each element's depletion from this sight-line parameter.
Abstract: A study of gas-phase element abundances reported in the literature for 17 different elements sampled over 243 sight lines in the local part of our Galaxy reveals that the depletions into solid form (dust grains) are extremely well characterized by trends that employ only three kinds of parameters. One is an index that describes the overall level of depletion applicable to the gas in any particular sight line, and the other two represent linear coefficients that describe how to derive each element's depletion from this sight-line parameter. The information from this study reveals the relative proportions of different elements that are incorporated into dust at different stages of grain growth. An extremely simple scheme is proposed for deriving the dust contents and metallicities of absorption-line systems that are seen in the spectra of distant quasars or the optical afterglows of gamma-ray bursts. Contrary to presently accepted thinking, the elements sulfur and krypton appear to show measurable changes in their depletions as the general levels of depletions of other elements increase, although more data are needed to ascertain whether or not these findings truly compelling. Nitrogen appears to show no such increase. The incorporation of oxygen into solid form in the densest gas regions far exceeds the amounts that can take the form of silicates or metallic oxides; this conclusion is based on differential measurements of depletion and thus is unaffected by uncertainties in the solar abundance reference scale.
547 citations
TL;DR: In this article, the authors presented 6-9 mum spectra of a sample of reflection nebulae, HII regions, YSOs, evolved stars and galaxies that show strong unidentified infrared bands, obtained with the SWS spectrograph on board ISO.
Abstract: IR spectroscopy provides a valuable tool for the characterisation and identification of interstellar molecular species. Here, we present 6-9 mum spectra of a sample of reflection nebulae, HII regions, YSOs, evolved stars and galaxies that show strong unidentified infrared bands, obtained with the SWS spectrograph on board ISO. The IR emission features in this wavelength region show pronounced variations. 1) The 6.2 mum feature shifts from 6.22 to 6.3 mum and clearly shows profile variations. 2) The 7.7 mum complex is comprised of at least two subpeaks peaking at 7.6 and one longwards of 7.7 mum. In some cases the main peak can apparently shift up to 8 mum. Two sources do not exhibit a 7.7 mum complex but instead show a broad emission feature at 8.22 mum. 3) The 8.6 mum feature has a symmetric profile in all sources and some sources exhibit this band at slightly longer wavelengths. For the 6.2, 7.7 and 8.6 mum features, the sources have been classified independently based on their profile and peak position. The classes derived for these features are directly linked with each other. Sources with a 6.2 mum feature peaking at similar to6.22 mum exhibit a 7.7 mum complex dominated by the 7.6 mum component. In contrast, sources with a 6.2 mum profile peaking longwards of 6.24 mum show a 7.7 mum complex with a dominant peak longwards of 7.7 mum and a 8.6 mum feature shifted toward the red. Furthermore, the observed 6-9 mum spectrum depends on the type of object. All ISM-like sources and a few PNe and Post-AGB stars belong to the first group while isolated Herbig AeBe stars, a few Post-AGB stars and most PNe belong to the second group. We summarise existing laboratory data and theoretical quantum chemical calculations of the modes emitting in this wavelength region of PAH molecules. We discuss the variations in peak position and profile in view of the exact nature of the carrier. We attribute the observed 6.2 mum profile and peak position to the combined effect of a PAH family and anharmonicity with pure PAHs representing the 6.3 mum component and substituted/complexed PAHs representing the 6.2 mum component. The 7.6 mum component is well reproduced by both pure and substituted/complexed PAHs but the 7.8 mum component remains an enigma. In addition, the exact identification of the 8.22 mum feature remains unknown. The observed variations in the characteristics of the IR emission bands are linked to the local physical conditions. Possible formation and evolution processes that may influence the interstellar PAH class are highlighted.
543 citations
TL;DR: In this article, the authors used high signal-to-noise ratio spectra of 20 H II regions in the giant spiral galaxy M101 to derive electron temperatures for the HII regions and robust metal abundances over radii R = 019-125R0 (6-41 kpc).
Abstract: We use high signal-to-noise ratio spectra of 20 H II regions in the giant spiral galaxy M101 to derive electron temperatures for the H II regions and robust metal abundances over radii R = 019-125R0 (6-41 kpc) We compare the consistency of electron temperatures measured from the [O III] ?4363, [N II] ?5755, [S III] ?6312, and [O II] ?7325 auroral lines Temperatures from [O III], [S III], and [N II] are correlated with relative offsets that are consistent with expectations from nebular photoionization models However, the temperatures derived from the [O II] ?7325 line show a large scatter and are nearly uncorrelated with temperatures derived from other ions We tentatively attribute this result to observational and physical effects, which may introduce large random and systematic errors into abundances derived solely from [O II] temperatures Our derived oxygen abundances are well fitted by an exponential distribution over six disk scale lengths, from approximately 13 (O/H)? in the center to 1/15 (O/H)? in the outermost region studied [for solar 12 + log(O/H) = 87] We measure significant radial gradients in N/O and He/H abundance ratios, but relatively constant S/O and Ar/O Our results are in approximate agreement with previously published abundances studies of M101 based on temperature measurements of a few H II regions However, our abundances are systematically lower by 02-05 dex than those derived from the most widely used strong-line empirical abundance indicators, again consistent with previous studies based on smaller H II region samples Independent measurements of the Galactic interstellar oxygen abundance from ultraviolet absorption lines are in good agreement with the Te-based nebular abundances We suspect that most of the disagreement with the strong-line abundances arises from uncertainties in the nebular models that are used to calibrate the empirical scale, and that strong-line abundances derived for H II regions and emission-line galaxies are as much as a factor of 2 higher than the actual oxygen abundances However, other explanations, such as the effects of temperature fluctuations on the auroral line based abundances, cannot be completely ruled out These results point to the need for direct abundance determinations of a larger sample of extragalactic H II regions, especially for objects more metal-rich than solar
467 citations
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01 Jan 1989
TL;DR: In this paper, a comparison of theory with observations internal dynamics of gaseous nebulae interstellar dust H II regions in the galactic context is presented. But the results are limited to the case of active galactic nuclei.
Abstract: Photoionization equilibrium thermal equilibrium calculation of emitted spectrum comparison of theory with observations internal dynamics of gaseous nebulae interstellar dust H II regions in the galactic context planetary nebulae nova and supernova remnants active galactic nuclei - diagnostic and physics active galactic nuclei - results.
6,090 citations
TL;DR: In this article, the current status of our knowledge of the chemical composition of the Sun is reviewed, essentially derived from the analysis of the solar photospheric spectrum, and a comparison of solar and meteoritic abundances confirms that there is a very good agreement between the two sets of abundances.
Abstract: We review the current status of our knowledge of the chemical composition of the Sun, essentially derived from the analysis of the solar photospheric spectrum. The comparison of solar and meteoritic abundances confirms that there is a very good agreement between the two sets of abundances. They are used to construct a Standard Abundance Distribution.
3,253 citations
01 Jan 1998
TL;DR: In this article, the current status of our knowledge of the chemical composition of the Sun is reviewed, essentially derived from the analysis of the solar photospheric spectrum, and a comparison of solar and meteoritic abundances confirms that there is a very good agreement between the two sets of abundances.
Abstract: We review the current status of our knowledge of the chemical composition of the Sun, essentially derived from the analysis of the solar photospheric spectrum. The comparison of solar and meteoritic abundances confirms that there is a very good agreement between the two sets of abundances. They are used to construct a Standard Abundance Distribution.
2,160 citations
TL;DR: In this paper, the authors investigated the relationship between the characteristic oxygen abundance, the radial abundance gradient, and the macroscopic properties of spiral galaxies by examining the properties of individual H II regions within those galaxies.
Abstract: We investigate the relationships between the characteristic oxygen abundance, the radial abundance gradient, and the macroscopic properties of spiral galaxies by examining the properties of individual H II regions within those galaxies Our observations of the line flux ratio (O II) lambda lambda 3726, 3729 + (O III) lambda lambda 4959, 5007)/H beta for 159 H II regions in 14 spiral galaxies are combined with published data to provide a sample of 39 disk galaxies for which (O II) + (O III)/H beta has been measured for at least five H II regions We find that the characteristic gas-phase abundances and luminosities of spiral galaxies are strongly correlated This relationship maps almost directly onto the luminosity-metallicity relationship of irregular galaxies and is also quite similar to that found for elliptical and dwarf spheroidal galaxies Within our sample of spirals, a strong correlation between characteristic abundance and Hubble type also exists The correlation between luminosity and Hubble type complicates the issue, but we discuss several interpretations of the correlations The relationship between circular velocity and characteristic abundance is also discussed We find that the slopes of the radial abundance gradients, when expressed in units of dex/isophotal radius, do not significantly correlate with either luminosity or Hubble type However, the hypothesis that both early and very late type spirals have shallower gradients than intermediate spirals is consistent with the data We find suggestive evidence that the presence of a bar induces a flatter gradient and also briefly discuss whether abundance gradients are exponential, as is usually assumed We investigate the properties of individual H II regions in a subset of 42 regions for which we have spectra that cover almost the entire spectral range from 3500 to 9800 A We use those data to estimate the densitites and ionizing spectra within the H II regions We confirm that the ionizing spectrum hardens with increasing radius and decreasing abundance We find no correlation between the ionization parameter and either radius or abundance, but this may be due to significant scatter introduced by the simple conversion of line ratios to ionization parameter
1,392 citations
TL;DR: The ultraviolet (UV) region of the spectrum has been crucial in providing information on the nature of the material and size distribution of the particles of interstellar dust before there were any measurements of the UV properties of interstellar extinction as mentioned in this paper.
Abstract: The ultraviolet (UV) region of the spectrum has been crucial in providing information on the nature of the material and size distribution of the particles of interstellar dust Before there were any measurements of the UV properties of interstellar extinction, interstellar particles were believed to be composed primarily of dirty ices The maximum of the interstellar extinction was believed to be at 03 μm, the shortest wavelength then observable Both of these predictions were quite wrong (as are probably many of our present ideas regarding dust) The first rocket measurement (Stecher, 1965) showed that there is a very strong extinction feature at 022 μm Now we also know the extinction increases dramatically towards the shortest wavelengths which can be reliably measured to date
1,351 citations