Planetary nebulae in the dwarf galaxy NGC 6822: Detection of new candidates

Aims. We aim to derive the chemical behavior of a significant sample of PNe and HII regions in the irregular galaxy NGC 6822. The selected objects are distributed in different zones of the galaxy. Our purpose is to obtain the chemical abundances of the present interstellar medium (ISM), represented by H ii regions, and the corresponding values at the time of formation of PNe. With these data the chemical homogeneity of NGC 6822 were tested and the abundance pattern given by H ii regions and PNe used as an observational constraint for computing chemical evolution models to infer the chemical history of NGC 6822.Methods. Due to the faintness of PNe and H ii regions in NGC 6822, to gather spectroscopic data with large telescopes is necessary.We obtained a well suited sample of spectra by employing VLT-FORS 2 and Gemini-GMOS spectrographs. Ionic and total abundances were calculated for the objects where electron temperatures could determined through the detection of [O iii] λ4363 or/and [N ii] λ5755 lines. A "simple" chemical evolution model was developed and the observed data were used to compute a model for NGC 6822 in order to infer a preliminary chemical history in this galaxy.Results. Confident determinations of He, O, N, Ne, S and Ar abundances were derived for a sample of 11 PNe and one H ii region. We confirm that the present ISM is chemically homogeneous, at least in the central 2 kpc of the galaxy, showing a value 12 + log O/H = 8.06 ± 0.04. From the abundance pattern of PNe, we identified two populations: a group of young PNe with abundances similar to H ii regions and a group of older objects with abundances a factor of two lower. A pair of extreme Type I PNe were found. No third dredge-up O enrichement was detected in PNe of this galaxy. The abundance determinations allow us to discuss the chemical behavior of the present and past ISM in NGC 6822. Our preliminary chemical evolution model predicts that an important gas-mass loss occurred during the first 5.3 Gyr, that no star higher than 40 M was formed, and that 1% of all 3-15 M stars became binary system progenitors of SNIa.

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“…A few faint nebulae were marked by Leisy et al (2005) as possible supernova remnants (SNR) due to their intense [S ii] lines.…”

Section: Supernova Remnants?mentioning

confidence: 99%

“…To accurately determine nebular abundances, data in a large wavelength range, at resolutions large enough to easily sepa- Leisy et al (2005) and in Paper I. The objects are designed as in Paper I, where the reader can find the cross-correlation with other names in the literature.…”

Section: Observations and Data Reductionmentioning

confidence: 99%

Chemical behavior of the dwarf irregular galaxy NGC6822. Its PN and HII region abundances

Hernández-Martínez

Peña²,

Carigi

et al. 2009

A&A

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“…The PN confirmed by spectroscopy (14 objects) are marked with a v in the last column of Table 2. We rediscovered all the 17 PN candidates reported by Leisy et al (2005), the PN found by Richer & McCall (2007) and all their HII regions.…”

Section: The Final Samples and Their Distributionmentioning

confidence: 99%

“…Leisy et al (2005), with 17 PN candidates, obtained a precarious PNLF for NGC 6822 which also presents a dip around 2 mag below the brightest PN. The main aim of this work is to investigate the PN populations in NGC 6822 by performing a deep survey for PN candidates.…”

Section: Introductionmentioning

confidence: 99%

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Emission line objects in NGC 6822. New planetary nebula candidates

Hernández-Martínez

Peña

2008

A&A

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Aims. Images obtained with the CTIO 4-m telescope and the MOSAIC-2 wide field camera in [O iii] 5007 and Hα on-band and off-band filters are analyzed to search for emission line objects in the dwarf galaxy NGC 6822. In particular we search for planetary nebula (PN) candidates. In addition, imaging and spectroscopy of a sub-sample of objects obtained with the ESO VLT and FORS 2 spectrograph are used to calibrate the MOSAIC imaging. Methods. In the continuum-subtracted images, a large number of line emission regions were detected, for which we measured instrumental magnitudes in all the filters. The [O iii] 5007 and Hα + [N ii] magnitudes were calibrated with the spectroscopy.Results. Based upon some criteria to distinguish between PNe and compact HII regions, we have found 26 PN candidates, increasing the known sample by 8 objects. Also we detected a number of compact HII regions and about 20 stellar-like objects emitting in Hα.For all the objects we present coordinates, instrumental magnitudes and nebular [O iii] and Hα + [N ii] fluxes. The observed luminosity function for the PN [O iii] 5007 magnitudes (PNLF) and the cumulative PNLF were calculated. We confirm that the PNLF presents a dip similar to the one detected for the Small Magellanic Cloud at 2.5 mag below the maximum. The cumulative PNLF returns a value M 5007 = −3.71 +0.21−0.42 for the peak absolute magnitude of the PNLF which is faint (but within uncertainties) compared to the value expected for galaxies with a metallicity similar to that of NGC 6822. From our best fit to the observed PNLF we obtained a rough estimate of the distance modulus m − M = 23.64 +0.23−0.43 mag, which agrees within uncertainties with recent values from Cepheid stars reported in the literature. Also the number of PNe in the brightest 0.5 mag, normalized to the galactic bolometric luminosity, was estimated to be α 0.5 ∼ (3.8 +0.90 −0.71 ) E-9. This number is similar to the values derived for galaxies with recent star formation and small galaxies (M B fainter than −18 mag) and larger than the values for early-type galaxies.

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The Extended Structure of Phoenix Dwarf Galaxy

Hidalgo

Aparicio

Martínez–Delgado

2003

Highlights of Spanish Astrophysics III

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We present the star formation history (SFH) and its variations with galactocentric distance for the Local Group dwarf galaxy of Phoenix. They have been derived from a (F555W, F814W) color-magnitude diagram (CMD) obtained from WFPC2@HST data which reaches the oldest main sequence turnoffs. The IAC-first (about 7 to 8 Gyr ago) in outer regions and the scale-length of the stellar mass density distribution decreased with time. Finally, no traces of a true, old halo are apparent in Phoenix either in its stellar age distribution or in the stellar mass density distribution, at least out to 0.5 kpc (about 2.5 scale-lengths) from the center.

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Planetary nebulae in the dwarf galaxy NGC 6822: Detection of new candidates

Abstract: Abstract. We have discovered 13 new candidate Planetary Nebulae (PNe) in the dwarf irregular galaxy NGC 6822, increasing its total number to 17 objects. Our sample of candidate PNe is complete down to 3.5 mag below the brightest PN.

Cited by 20 publications

References 44 publications

Chemical behavior of the dwarf irregular galaxy NGC6822. Its PN and HII region abundances

Chemical behavior of the dwarf irregular galaxy NGC6822. Its PN and HII region abundances

Emission line objects in NGC 6822. New planetary nebula candidates

The Extended Structure of Phoenix Dwarf Galaxy

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