scholarly journals A Local Group Polar Ring Galaxy: NGC 6822

2005 ◽  
Vol 636 (2) ◽  
pp. L85-L88 ◽  
Author(s):  
Serge Demers ◽  
Paolo Battinelli ◽  
William E. Kunkel
Keyword(s):  
Local Group ◽  
Polar Ring ◽  
Ngc 6822

Discovery of Latent Star Formation in the Extended H i Gas around the Local Group Dwarf Irregular Galaxy NGC 6822

2003 ◽  
Vol 590 (1) ◽  
pp. L17-L20 ◽  
Author(s):  
Yutaka Komiyama ◽  
Sadanori Okamura ◽  
Masafumi Yagi ◽  
Hisanori Furusawa ◽  
Mamoru Doi ◽  
...  
Keyword(s):  
Star Formation ◽  
Local Group ◽  
Irregular Galaxy ◽  
Ngc 6822

scholarly journals Planetary Nebulae in Local Group Galaxies

1983 ◽  
Vol 103 ◽  
pp. 443-460
Author(s):  
Holland C. Ford
Keyword(s):  
Local Group ◽  
Planetary Nebulae ◽  
Stellar Populations ◽  
Chemical Compositions ◽  
H Ii Regions ◽  
Helium Abundance ◽  
Abundance Gradient ◽  
Star Forming ◽  
Ic 10 ◽  
Ngc 6822

Recent surveys for planetary nebulae have given the first identifications in Fornax, NGC 6822, M33, IC 10, Leo A, Sextans A, Pegasus, WLM, NGC 404, and M81, and extended the identifications in the SMC, the LMC, and M31. Observations of planetaries have established chemical compositions in old or intermediate age populations in 8 Local Group galaxies. The chemical compositions show that i) the helium abundance is higher in planetary nebulae than in H II regions in the same galaxy, and ii) nitrogen is overabundant relative to H II regions by factors of 4 to 100. Planetary nebulae are not a major source of helium in star-forming galaxies, and are a major source of nitrogen. The planetary in Fornax has a relatively high O abundance, and, together with Fornax's carbon stars, establishes the presence of at least 2 stellar populations. The abundance gradient derived from 3 planetaries in M31 is very shallow, and gives high abundances at ~ 20 kpc. By using planetary nebulae as standard candles, upper and lower distance limits have been set for 10 Local Group candidates, and a new distance estimated for M81.

Sardinia Radio Telescope (SRT) observations of Local Group dwarf galaxies

2017 ◽  
Vol 13 (S336) ◽  
pp. 109-112
Author(s):  
A. Tarchi ◽  
P. Castangia ◽  
G. Surcis ◽  
A. Brunthaler ◽  
K. M. Menten ◽  
...  
Keyword(s):  
Radio Telescope ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Radio Continuum ◽  
Maser Emission ◽  
Star Forming ◽  
Star Forming Regions ◽  
First Results ◽  
Ngc 6822 ◽  
Almost All

AbstractThe dwarf galaxies in the Local Group (LG) reveal a surprising amount of spatial structuring. In particular, almost all non-satellite dwarfs belong to one of two planes that show a very pronounced symmetry. In order to determine if these structures in the LG are dynamically stable or, alternatively, if they only represent transient alignments, proper motion measurements of these galaxies are required. A viable method to derive proper motions is offered by VLBI studies of 22-GHz water (and 6.7-GHz methanol) maser lines in star-forming regions.In 2016, in the framework of the Early Science Program of the Sardinia Radio Telescope (SRT), we have conducted an extensive observational campaign to map the entire optical body of all the LG dwarf galaxies that belong to the two planes, at C and K band, in a search for methanol and water maser emission.Here, we outline the project and present its first results on 3 targets, NGC 6822, IC 1613, and WLM. While no luminous maser emission has been detected in these galaxies, a number of interesting weaker detections has been obtained, associated with particularly active star forming regions. In addition, we have produced deep radio continuum maps for these galaxies, aimed at investigating their star forming activity and providing an improved assessment of star formation rates in these galaxies.

scholarly journals Chemical abundances of massive stars in Local Group galaxies

2003 ◽  
Vol 212 ◽  
pp. 30-37 ◽  
Author(s):  
Kim A. Venn ◽  
Andreas Kaufer ◽  
Eline Tolstoy ◽  
Rolf-Peter Kudritzki ◽  
Norbert Przybilla ◽  
...  
Keyword(s):  
High Efficiency ◽  
Local Group ◽  
Iron Group ◽  
Chemical Abundances ◽  
Elemental Abundances ◽  
Irregular Galaxies ◽  
Ngc 6822 ◽  
Process Elements ◽  
Star Formation Histories ◽  
Dwarf Irregular Galaxies

The relative abundances of elements in galaxies can provide valuable information on the stellar and chemical evolution of a galaxy. While nebulae can provide abundances for a variety of light elements, stars are the only way to directly determine the abundances of iron-group and s-process and r-process elements in a galaxy. The new 8m and 10m class telescopes and high-efficiency spectrographs now make high-quality spectral observations of bright supergiants possible in dwarf galaxies in the Local Group. We have been concentrating on elemental abundances in the metal-poor dwarf irregular galaxies, NGC 6822, WLM, Sextants A, and GR 8. Comparing abundance ratios to those predicted from their star formation histories, determined from color-magnitude diagrams, and comparing those ratios between these galaxies can give us new insights into the evolution of these dwarf irregular galaxies. Iron-group abundances also allow us to examine the metallicities of the stars in these galaxies directly, which affects their inferred mass loss rates and predicted stellar evolution properties.

scholarly journals Massive young stellar objects in the Local Group irregular galaxy NGC 6822 identified using machine learning

2021 ◽  
Vol 507 (4) ◽  
pp. 5106-5131
Author(s):  
David A Kinson ◽  
Joana M Oliveira ◽  
Jacco Th van Loon
Keyword(s):  
Machine Learning ◽  
Star Formation ◽  
Local Group ◽  
Point Sources ◽  
Asymptotic Giant Branch ◽  
Supervised Machine Learning ◽  
Young Stellar Objects ◽  
Irregular Galaxy ◽  
Stellar Objects ◽  
Ngc 6822

ABSTRACT We present a supervised machine learning methodology to classify stellar populations in the Local Group dwarf-irregular galaxy NGC 6822. Near-IR colours (J − H, H − K, and J − K), K-band magnitudes and far-IR surface brightness (at 70 and 160 $\mu$m) measured from Spitzer and Herschel images are the features used to train a Probabilistic Random Forest (PRF) classifier. Point-sources are classified into eight target classes: young stellar objects (YSOs), oxygen- and carbon-rich asymptotic giant branch stars, red giant branch and red supergiant stars, active galactic nuclei, massive main-sequence stars, and Galactic foreground stars. The PRF identifies sources with an accuracy of ∼ 90 per cent across all target classes rising to ∼96 per cent for YSOs. We confirm the nature of 125 out of 277 literature YSO candidates with sufficient feature information, and identify 199 new YSOs and candidates. Whilst these are mostly located in known star-forming regions, we have also identified new star formation sites. These YSOs have mass estimates between ∼15 and 50 M⊙, representing the most massive YSO population in NGC 6822. Another 82 out of 277 literature candidates are definitively classified as non-YSOs by the PRF analysis. We characterize the star formation environment by comparing the spatial distribution of YSOs to those of gas and dust using archival images. We also explore the potential of using (unsupervised) t-distributed stochastic neighbour embedding maps for the identification of the same stellar population classified by the PRF.

scholarly journals Sardinia Radio Telescope observations of Local Group dwarf galaxies – I. The cases of NGC 6822, IC 1613, and WLM

2019 ◽  
Vol 492 (1) ◽  
pp. 45-57
Author(s):  
A Tarchi ◽  
P Castangia ◽  
G Surcis ◽  
A Brunthaler ◽  
C Henkel ◽  
...  
Keyword(s):  
Local Group ◽  
Dwarf Galaxies ◽  
Radio Continuum ◽  
Star Forming ◽  
Star Forming Regions ◽  
Long Baseline ◽  
Planar Structures ◽  
Ngc 6822 ◽  
Almost All ◽  
Transient Alignment

ABSTRACT Almost all dwarf galaxies in the Local Group (LG) that are not satellites of the Milky Way or M 31 belong to either one of two highly symmetric planes. It is still a matter of debate whether these planar structures are dynamically stable or whether they only represent a transient alignment. Proper motions, if they could be measured, could help to discriminate between these scenarios. Such motions could be determined with multi-epoch very long baseline interferometry (VLBI) of sources that show emission from water and methanol at frequencies of 22 and 6.7 GHz, respectively. We report searches for such masers. We have mapped three LG galaxies, NGC 6822, IC 1613, and WLM, in the bands covering the water vapour and methanol lines. These systems are members of the two above-mentioned planes of galaxies. We have produced deep radio continuum (RC) maps and spectral line cubes. The former have been used to identify star-forming regions and to derive global galactic star formation rates (SFRs). These SFRs turn out to be lower than those determined at other wavelengths in two of our sources. This indicates that dwarf galaxies may follow predictions on the RC–SFR relation only in individual regions of enhanced RC emission, but not when considering the entire optical body of the sources. No methanol or water maser emission has been confidently detected, down to line luminosity limits of ∼4 × 10−3 and 10 × 10−3 L⊙, respectively. This finding is consistent with the small sizes, low SFRs, and metallicities of these galaxies.

The Local Group Dwarf Irregular Galaxy NGC 6822.III. The Recent Star Formation History

1996 ◽  
Vol 112 ◽  
pp. 2596 ◽  
Author(s):  
C. Gallart ◽  
A. Aparicio ◽  
G. Bertelli ◽  
C. Chiosi
Keyword(s):  
Star Formation ◽  
Local Group ◽  
Star Formation History ◽  
Irregular Galaxy ◽  
Formation History ◽  
Ngc 6822

scholarly journals Chemical and Photometric Evolution of the Local Group Galaxy NGC 6822 in a Cosmological Context

2006 ◽  
Vol 644 (2) ◽  
pp. 924-939 ◽  
Author(s):  
Leticia Carigi ◽  
Pedro Colin ◽  
Manuel Peimbert
Keyword(s):  
Local Group ◽  
Cosmological Context ◽  
Ngc 6822 ◽  
Group Galaxy ◽  
Local Group Galaxy

scholarly journals Planetary Nebulae as a Probe of the Local Group Galaxies Evolution

2006 ◽  
Vol 2 (S235) ◽  
pp. 215-215
Author(s):  
A. Y. Kniazev ◽  
S. A. Pustilnik ◽  
E. K. Grebel ◽  
D. B. Zucker ◽  
P. Vaisanen
Keyword(s):  
Local Group ◽  
Planetary Nebulae ◽  
Ic 10 ◽  
Irregular Galaxies ◽  
Ngc 6822 ◽  
Dwarf Irregular Galaxies

AbstractWe present the latest results from our study of PNe and HII regions in two Local Group dwarf irregular galaxies IC 10 and NGC 6822.

scholarly journals Stellar Content of Local Group Galaxies - An Introduction

1999 ◽  
Vol 192 ◽  
pp. 3-16 ◽  
Author(s):  
Sidney van den Bergh
Keyword(s):  
Milky Way ◽  
Local Group ◽  
Large Fraction ◽  
Polar Group ◽  
Stellar Content ◽  
Groups Of Galaxies ◽  
Ic 10 ◽  
Sky Survey ◽  
Group Members ◽  
Ngc 6822

In The Realm of the Nebulae, Hubble (1936) first drew attention to the fact that the Milky Way system and the Andromeda galaxy belong to a small cluster that also contains M32, M33, the Magellanic Clouds, NGC 205, NGC 6822 and IC 1613. Hubble also listed IC 10 as a possible member of what he referred to as “the Local Group”. Inspection of the prints of the Palomar Sky Survey shows (van den Bergh 1962) that a large fraction of all field galaxies are located in such small groups or clusters. Our Milky Way system therefore appears to be situated in a rather typical region of space. All of the well-established Local Group members that are listed above are at distances D ≤ 1.0 Mpc. A conservative limit D < 1.5 Mpc may therefore be used to search for new Local Group members. An additional criterion for physical membership in the Local Group is that a candidate member with solar apex distance θ and radial velocity Vr should lie close to the Vr versus cos θ relation for well-established Local Group members (Courteau & van den Bergh 1999). Finally candidates may be disqualified from membership if they appear projected on nearby groups of galaxies that are centered at distances greater than 1.5 Mpc. In particular the Local Group candidates NGC 1560, NGC 1569, UGC-A86 and Cassiopeia 1 were excluded because they appear projected on (or near) the IC 342/Maffei group. Furthermore NGC 55 and UKS 2323-326 were excluded because they appear projected on (or near) the Sculptor (= South Polar) group. Observational data on 35 probable Local Group members are given in Table 1.

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