The chemical abundances in a sample of dwarf irregular galaxies

Hidalgo-Gámez, A. M.; Olofsson, Katarina; Masegosa, J.

doi:10.1051/0004-6361:20010063

Cited by 20 publications

(17 citation statements)

References 58 publications

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“…The intrinsic errors associated with bright-line abundances are of order 0.05 dex; in this plot, we have assigned 0.20 dex uncertainties from the bright-line method. In addition to the stellar abundances from Venn et al (2001), we have also plotted oxygen abundances reported by Smith (1975), Lequeux et al (1979), Pagel et al (1980), Skillman et al (1989), Richer & McCall (1995), Miller (1996), Chandar et al (2000), Hidalgo-Gámez et al (2001), Lee et al (2003d), and Peimbert et al (2005). Oxygen abundances for H II regions at radii 0.5 kpc are in agreement with abundances derived for A-type supergiants at similar radii.…”

Section: Interstellar Medium and Stellar Oxygen Abundances In Ngc 6822supporting

confidence: 82%

“…4. Hidalgo-Gámez et al (2001) also obtained spectra of Hubble V and Hubble X, and while there were no large differences in oxygen abundances between the two H II regions, they claimed small-scale abundances variations on < 10 pc length scales. Nollenberg et al (2002) derived sulfur abundances from ISO measurements of [S III] and [S IV] emission lines in the mid-infrared, and showed that the S +3 ion is the largest contributor to the total sulfur abundance in extragalactic H II regions.…”

Section: Introductionmentioning

confidence: 97%

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The Spatial Homogeneity of Nebular and Stellar Oxygen Abundances in the Local Group Dwarf Irregular Galaxy NGC 6822

Lee

Skillman

Venn

2006

ApJ

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To test the existence of a possible radial gradient in oxygen abundances within the Local Group dwarf irregular galaxy NGC 6822, we have obtained optical spectra of 19 nebulae with the EFOSC2 spectrograph on the 3.6-m telescope at ESO La Silla. The extent of the measured nebulae spans galactocentric radii in the range between 0.05 kpc and 2 kpc (over four exponential scale lengths). In five H II regions (Hubble I, Hubble V, Kα, Kβ, KD 28e), the temperature-sensitive [O III] λ4363 emission line was detected, and direct oxygen abundances were derived. Oxygen abundances for the remaining H II regions were derived using bright-line methods. The oxygen abundances for three A-type supergiant stars are slightly higher than nebular values at comparable radii. Linear least-square fits to various subsets of abundance data were obtained. When all of the measured nebulae are included, no clear signature is found for an abundance gradient. A fit to only newly observed H II regions with [O III] λ4363 detections yields an oxygen abundance gradient of −0.14 ± 0.07 dex kpc −1 . The gradient becomes slightly more significant (−0.16 ± 0.05 dex kpc −1 ) when three additional H II regions with [O III] λ4363 measurements from the literature are added. Assuming no abundance gradient, we derive a mean nebular oxygen abundance 12+log(O/H) = 8.11 ± 0.10 from [O III] λ4363 detections in the five H II regions from our present data; this mean value corresponds to [O/H] = −0.55. 3.1.1. Oxygen Abundances: [O III] λ4363 Temperatures The "direct" conversion of emission-line intensities into ionic abundances requires a reliable estimate of the electron temperature of the ionized gas. We adopt a two-zone model for H II regions, with a low-and a high-ionization zone characterized by temperatures T e (O + ) and T e (O +2 ), respectively. The temperature in the O +2 zone is measured with the emission-line ratio I([O III] λ5007)/I([O III] λ4363) (Os terbrock 1989). The temperature in the O + zone is given bywhere t e = T e /10 4 K (Campbell et al. 1986;Garnett 1992). The total oxygen abundance by number is given by O/H = O + /H + + O +2 /H + . For conditions found in typical H II regions and those presented here, very little oxygen in neutral form is expected, and in the absence of He II emission, the O +3 contribution is considered negligible. For subsequent calculations of ionic abundances, we assume the following electron temperatures for specific ions (Garnett 1992;Thuan et al. 1995):, t e (Ar +2 ) = 0.83 t e (O +2 ) + 0.17, and t e (Ar +3 ) = t e (O +2 ).Derived ionic and total abundances are listed in Tables 6a and 6b, which include derived O + and O +2 electron temperatures, O + and O +2 ionic abundances, and the total oxygen abundances. Direct H II region oxygen abundances were derived for Hubble I, Hubble V, Kα, Kβ, and KD 28e, and were in excellent agreement with those derived from the method described by Skillman et al. (2003).Where [S II] λλ4068,4076 and [O II] λλ7320,7330 were detected in the spectra for Hubble V, Kα, and KD 28e, we used ...

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Section: Interstellar Medium and Stellar Oxygen Abundances In Ngc 6822supporting

confidence: 82%

Section: Introductionmentioning

confidence: 97%

The Spatial Homogeneity of Nebular and Stellar Oxygen Abundances in the Local Group Dwarf Irregular Galaxy NGC 6822

Lee

Skillman

Venn

2006

ApJ

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“…Pastoriza & Dottori (1981), Stasinska et al (1986), Hidalgo- Gámez et al (2002) have proposed that region D may be either a chemically and kinematically distinct complex within IC 4662, or a close companion object. The latter possibility is particularly interesting in view of the hypothesis that very close, gas-rich dwarf companions might be conceivable triggering agents of starburst activity in BCDs (Taylor et al 1995;Pustilnik et al 2001;Noeske et al 2001).…”

Section: Ic4662 (Eso 102-g014 He 2-269)mentioning

confidence: 99%

New insights to the photometric structure of Blue Compact Dwarf galaxies from deep Near-Infrared studies

Noeske

Papaderos

Cairós

et al. 2003

A&A

102

158

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Abstract.We have analyzed deep Near Infrared (NIR) broad band images for a sample of Blue Compact Dwarf Galaxies (BCDs), observed with the ESO NTT and Calar Alto 3.6 m telescopes. The data presented here allows for the detection and quantitative study of the extended stellar low-surface brightness (LSB) host galaxy in all sample BCDs. NIR surface brightness profiles (SBPs) of the LSB host galaxies agree at large galactocentric radii with those from optical studies, showing also an exponential intensity decrease and compatible scale lengths. At small to intermediate radii (within 1-3 exponential scale lengths), however, the NIR data reveals for more than one half of our sample BCDs evidence for a significant flattening of the exponential profile of the LSB component. Such profiles (type V SBPs, Binggeli & Cameron 1991) have rarely been detected in the LSB component of BCDs at optical wavelengths, where the relative flux contribution of the starburst, being stronger than in the NIR, can readily hide a possible central intensity depression in the underlying LSB host. The structural properties, frequency and physical origin of type V LSB profiles in BCDs and dwarf galaxies in general have not yet been subject to systematic studies. Nevertheless, the occurrence of such profiles in an appreciable fraction of BCDs would impose important new observational constraints to the radial mass distribution of the stellar LSB component, as well as to the photometric fading of these systems after the termination of star-forming activities. We test the suitability of two empirical fitting functions, a modified exponential distribution (Papaderos et al. 1996a) and the Sérsic law, for the systematization of the structural properties of BCD host galaxies which show a type V intensity distribution. Either function has been found to satisfactorily fit a type V distribution. However, it is argued that the practical applicability of Sérsic fits to the LSB emission of BCDs is limited by the extreme sensitivity of the achieved solutions to, e.g., small uncertainties in the sky subtraction and SBP derivation. We find that most of the sample BCDs show in their stellar LSB host galaxy optical-NIR colors indicative of an evolved stellar population with subsolar metallicity. Unsharp-masked NIR maps reveal numerous morphological details and indicate in some cases, in combination with optical data, appreciable non-uniform dust absorption on a spatial scale as large as ∼1 kpc.

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“…More data exist for H  regions (Lequeux et al 1980;Hodge et al 1989;Chandar et al 2000;Hidalgo-Gámez et al 2001;O'Dell et al 1999), but a comprehensive, homogeneous and accurate H  abundance database is still missing. New abundance determinations for both PNe and H  regions are clearly needed in order to allow a proper comparison with the recent determinations for individual B (Muschielok et al 1999) or A (Venn et al 2003) supergiant stars.…”

Section: Introductionmentioning

confidence: 99%