Software for the Analysis of Emission Line Nebulae

Shaw, Richard A.; Dufour, R. J.

doi:10.1086/133637

Cited by 426 publications

(375 citation statements)

References 15 publications

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“…The line can be affected by imperfect sky subtraction of the Hg λ4358 sky line, and we decided not to use it. In order to calculate the physical conditions and the ionic oxygen abundances in these 12 H ii regions, we use the tasks available in the nebular package of iraf, originally based on the calculations of De Robertis, Dufour & Hunt (1987) and Shaw & Dufour (1995). We adopted the following atomic data: the transition probabilities of Zeippen (1982) for O + , Wiese, Fuhr & Deters (1996) and Storey & Zeippen (2000) for O ++ , Wiese et al (1996) for N + and Mendoza & Zeippen (1982) for S + ; and the effective collision strengths of Pradhan et al (2006) for O + , Aggarwal & Keenan (1999) for O ++ , Lennon & Burke (1994) for N + , and Keenan et al (1996) for S + .…”

Section: The Direct Methodsmentioning

confidence: 99%

The oxygen abundance gradient in M81 and the robustness of abundance determinations in H ii regions

Arellano-Córdova

Rodríguez

Mayya

et al. 2015

Mon. Not. R. Astron. Soc.

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We study the sensitivity of the methods available for abundance determinations in H ii regions to potential observational problems. We compare the dispersions they introduce around the oxygen and nitrogen abundance gradients when applied to five different sets of spectra of H ii regions in the galaxy M81. Our sample contains 116 H ii regions with galactocentric distances of 3 to 33 kpc, including 48 regions observed by us with the OSIRIS long-slit spectrograph at the 10.4-m Gran Telescopio Canarias telescope. The direct method can be applied to 31 regions, where we can get estimates of the electron temperature. The different methods imply oxygen abundance gradients with slopes of −0.010 to −0.002 dex kpc −1 , and dispersions in the range 0.06-0.25 dex. The direct method produces the shallowest slope and the largest dispersion, illustrating the difficulty of obtaining good estimates of the electron temperature. Three of the strong-line methods, C, ONS, and N2, are remarkably robust, with dispersions of ∼ 0.06 dex, and slopes in the range −0.008 to −0.006 dex kpc −1 . The robustness of each method can be directly related to its sensitivity to the line intensity ratios that are more difficult to measure properly. Since the results of the N2 method depend strongly on the N/O abundance ratio and on the ionization parameter, we recommend the use of the C and ONS methods when no temperature estimates are available or when they have poor quality, although the behaviour of these methods when confronted with regions that have different properties and different values of N/O should be explored.

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Section: The Direct Methodsmentioning

confidence: 99%

The oxygen abundance gradient in M81 and the robustness of abundance determinations in H ii regions

Arellano-Córdova

Rodríguez

Mayya

et al. 2015

Mon. Not. R. Astron. Soc.

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“…The electron densities n e were calculated from the [SII]λλ6717, 31 line ratios using the temden task within IRAF/STSDAS (Shaw & Dufour 1995), and assuming an electronic temperature T e = 10 000 K. This was possible only for some galaxies in our sample (see Table 5), because the quality of our spectra is significantly poorer redward of ∼6600 Å, and telluric absorption lines around 6800 Å prevent in many cases a reliable fit to the [SII] doublet. The derived electron densities are given in Table 5.…”

Section: Agn Calibrationmentioning

confidence: 99%

Nearby early-type galaxies with ionized gas

Annibali

Bressan

Rampazzo

et al. 2010

A&A

121

162

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Aims. A significant fraction of early-type galaxies (ETGs) exhibit emission lines in their optical spectra. We attempt to identify the producing the emission mechanism and the ionized gas in ETGs, and its connection with the host galaxy evolution. Methods. We analyzed intermediate-resolution optical spectra of 65 ETGs, mostly located in low density environments and exhibiting spectros-copic diagnostic lines of ISM from which we had previously derived stellar population properties. To extract the emission lines from the galaxy spectra, we developed a new fitting procedure that accurately subtracts the underlying stellar continuum, and accounts for the uncertainties caused by the age-metallicity degeneracy. Results. Optical emission lines are detected in 89% of the sample. The incidence and strength of emission correlate with neither the E/S0 classification, nor the fast/slow rotator classification. By means of the classical [OIII]/Hβ versus [NII]/Hα diagnostic diagram, the nuclear galaxy activity is classified such that 72% of the galaxies with emission are LINERs, 9% are Seyferts, 12% are composite/transition objects, and 7% are non-classified. Seyferts have young luminostiy-weighted ages ( 5 Gyr), and appear, on average, significantly younger than LINERs and composites. Excluding the Seyferts from our sample, we find that the spread in the ([OIII], Hα, or [NII]) emission strength increases with the galaxy central velocity dispersion σ c . Furthermore, the [NII]/Hα ratio tends to increase with σ c . The [NII]/Hα ratio decreases with increasing galactocentric distance, indicative of either a decrease in the nebular metallicity, or a progressive "softening" of the ionizing spectrum. The average nebular oxygen abundance is slightly less than solar, and a comparison with the results obtained in Paper III from Lick indices shows that it is ≈0.2 dex lower than that of stars. Conclusions. The nuclear (r < r e /16) emission can be attributed to photoionization by PAGB stars alone only for ≈22% of the LINER/composite sample. On the other hand, we cannot exclude an important role of PAGB star photoionization at larger radii. For the major fraction of the sample, the nuclear emission is consistent with excitation caused by either a low-accretion rate AGN or fast shocks (200-500 km s −1 ) in a relatively gas poor environment (n 100 cm −3 ), or both. The derived [SII]6717/6731 ratios are consistent with the low gas densities required by the shock models. The derived nebular metallicities are indicative of either an external origin of the gas, or an overestimate of the oxygen yields by SN models.

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“…The quoted uncertainties account for measurement and reddening coefficient errors. Electron densities, electron temperatures and ionic abundances of the ionized gas were derived using the IRAF nebular package (Shaw & Dufour 1994). We obtained the electron densities, n e , from the [SII]λ6717/λ6731 line ratio.…”

Section: Nebular Propertiesmentioning

confidence: 99%

Gemini GMOS spectroscopy of HeII nebulae in M 33

Kehrig

Oey

Crowther

et al. 2011

A&A

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We have carried out a narrow-band survey of the Local Group galaxy, M 33, in the HeII λ4686 emission line, to identify HeII nebulae in this galaxy. With spectroscopic follow-up observations, we confirm three of seven candidate objects, including identification of two new HeII nebulae, BCLMP651, HBW673. We also obtain spectra of associated ionizing stars for all the HII regions, identifying two new WN stars. We demonstrate that the ionizing source for the known HeII nebula, MA 1, is consistent with being the earlytype WN star MC8 (M 33-WR14), by carrying out a combined stellar and nebular analysis of MC8 and MA 1. We were unable to identify the helium ionizing sources for HBW 673 and BCLMP 651, which do not appear to be Wolf-Rayet stars. According to the [OIII]λ5007/Hβ vs.[NII]λ6584/Hα diagnostic diagram, excitation mechanisms apart from hot stellar continuum are needed to account for the nebular emission in HBW 673, which appears to have no stellar source at all.

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Software for the Analysis of Emission Line Nebulae

Cited by 426 publications

References 15 publications

The oxygen abundance gradient in M81 and the robustness of abundance determinations in H ii regions

The oxygen abundance gradient in M81 and the robustness of abundance determinations in H ii regions

Nearby early-type galaxies with ionized gas

Gemini GMOS spectroscopy of HeII nebulae in M 33

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