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

Lee, Henry; Skillman, Evan D.; Venn, Kim A.

doi:10.1086/500568

Cited by 79 publications

(98 citation statements)

References 92 publications

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“…We find an average metallicity for our sample of Z [ ] = −0.52 ± 0.21, which agrees well with the results derived from BSGs (Muschielok et al 1999;Venn et al 2001;Przybilla 2002) and H II regions (Lee et al 2006).…”

Section: Metallicity Measurementssupporting

confidence: 92%

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Red Supergiant Stars as Cosmic Abundance Probes: Kmos Observations in NGC 6822

Patrick

Evans

Davies

et al. 2015

ApJ

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We present near-IR spectroscopy of red supergiant (RSG) stars in NGC 6822, obtained with the new K-band Multi-Object Spectrograph Very Large Telescope, Chile. From comparisons with model spectra in the J-band we determine the metallicity of 11 RSGs, finding a mean value of [Z] = −0.52 ± 0.21, which agrees well with previous abundance studies of young stars and H II regions. We also find an indication for a low-significance abundance gradient within the central 1 kpc. We compare our results with those derived from older stellar populations and investigate the difference using a simple chemical evolution model. By comparing the physical properties determined for RSGs in NGC 6822 with those derived using the same technique in the Galaxy and the Magellanic Clouds, we show that there appears to be no significant temperature variation of RSGs with respect to metallicity, in contrast to recent evolutionary models.

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Section: Metallicity Measurementssupporting

confidence: 92%

“…In contrast, Lee et al (2006) used the oxygen abundances from 19 H II regions and found no clear evidence for a metallicity gradient. Using a subset of the highest quality H II region data available, these authors found a gradient of −0.16 ± 0.05 dex kpc −1 .…”

Section: Metallicity Measurementsmentioning

confidence: 99%

Red Supergiant Stars as Cosmic Abundance Probes: Kmos Observations in NGC 6822

Patrick

Evans

Davies

et al. 2015

ApJ

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“…8) is similar to those of irregular galaxies (Fukugita et al 1995), and its absolute magnitude (∼ −13) is located at the faint end of the luminosity function of extremely low-luminosity galaxies (Blanton et al 2005). Its metallicity is low (see §3.3), and is comparable to those of local dwarf irregular galaxy (e.g., NGC 6822; Lee et al 2006). Its warm infrared color (high F 24µm /F 8µm ratio; see next subsection) is also consistent with that of irregular galaxies (e.g., DDO 053) in the Spitzer Infrared Nearby Galaxies Survey (SINGS, Kennicutt et al 2003;Dale et al 2005).…”

Section: Possible Formation Scenarios Of the Yscs In Arp 24mentioning

confidence: 74%

Multiwavelength Study of Young Massive Star Clusters in the Interacting Galaxy Arp 24

Cao

2007

Astron J

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We made a multi-wavelength study of young massive star clusters (YSCs) in the interacting galaxy ARP 24, using the optical and ultraviolet images from Hubble Space Telescope (HST), Sloan Digital Sky Survey, and Galaxy Evolution Explorer; the mid-infrared images from Spitzer Space Telescope; and the narrowband Hα image and optical spectra from the NAOC 2.16 m telescope. Based on the HST images, we found that the brightest infrared knot in ARP 24 is associated with a complex of five young massive star clusters, within a region of ∼ 0.95 ′′ radius (127pc) in size. The ages and masses of the star clusters in this complex and other regions were estimated using HST broadband photometries and the Starburst99 synthesis models. The star clusters in this complex are very young (within ages of ∼ 3-5 Myr) and massive (masses of ∼10 5 M ⊙ ). The ionization parameter and metallicity of the complex were estimated using the emission line ratios, and the star formation rates were calculated using monochromatic 24µm, FUV, and Hα line luminosities. We speculate that ARP 24 may formed by a retrograde fly-by encounter indicated by its one-armed appearance and fanlike structure, and the formation of the YSCs in this galaxy is triggered by the interaction. The clusters in the YSC complex may formed in a single giant molecular cloud simultaneously. From the ultraviolet to mid-infrared spectral energy distributions, we found that the region of the YSC complex is relatively bluer in optical and has higher 24µm dust emission relative to the starlight and 8µm emission. This warm infrared color may due to strong UV radiation field or other mechanisms (e.g., shocks) within this region which may destroy the Polycyclic Aromatic Hydrocarbons and enhance the small grain emission at 24µm.

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“…There are some exceptions, such as, for instance, the observed oxygen gradient in NGC 6822 (Venn et al 2004;Lee et al 2006) and in the dwarf blue compact galaxy NGC1750 (Annibali et al 2015), or the iron gradients in the SMC, in the LMC, and in the dIrr WLM (Leaman et al 2014). The systematic study of gradients in late-type spiral and irregular galaxies by Pilyugin et al (2014Pilyugin et al ( , 2015 has shown that there is a strong correlation between the radial abundance gradient of galaxies and their surface brightness profiles.…”

Section: Discussionmentioning

confidence: 99%

NGC 55: a disc galaxy with flat abundance gradients

Magrini

Gonçalves

Vajgel

2016

Mon. Not. R. Astron. Soc.

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We present new spectroscopic observations obtained with GMOS@Gemini-S of a sample of 25 H ii regions located in NGC 55, a late-type galaxy in the nearby Sculptor group. We derive physical conditions and chemical composition through the T e -method for 18 H ii regions, and strong-line abundances for 22 H ii regions. We provide abundances of He, O, N, Ne, S, Ar, finding a substantially homogenous composition in the ionised gas of the disc of NGC 55, with no trace of radial gradients. The oxygen abundances, both derived with T e -and strong-line methods, have similar mean values and similarly small dispersions: 12+log(O/H)=8.13±0.18 dex with the former and 12+log(O/H)=8.17±0.13 dex with the latter. The average metallicities and the flat gradients agree with previous studies of smaller samples of H ii regions and there is a qualitative agreement with the blue supergiant radial gradient as well. We investigate the origin of such flat gradients comparing NGC 55 with NGC 300, its companion galaxy, which is also twin of NGC 55 in terms of mass and luminosity. We suggest that the differences in the metal distributions in the two galaxies might be related to the differences in their K-band surface density profile. The flatter profile of NGC 55 probably causes in this galaxy higher infall/outflow rates than in similar galaxies. This likely provokes a strong mixing of gas and a re-distribution of metals.

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

Cited by 79 publications

References 92 publications

Red Supergiant Stars as Cosmic Abundance Probes: Kmos Observations in NGC 6822

Red Supergiant Stars as Cosmic Abundance Probes: Kmos Observations in NGC 6822

Multiwavelength Study of Young Massive Star Clusters in the Interacting Galaxy Arp 24

NGC 55: a disc galaxy with flat abundance gradients

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