Star complexes and stellar populations in NGC 6822

Karampelas, A.; Dapergolas, A.; Kontizas, E.; Livanou, E.; Kontizas, M.; Bellas‐Velidis, I.; Vı́lchez, J. M.

doi:10.1051/0004-6361/200811081

Cited by 15 publications

(26 citation statements)

References 27 publications

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“…For the same galaxy, Battinelli et al (1996) found hierarchical structures on two levels, the first with size ∼100 pc and the second with a distribution of sizes from ∼100 to ∼800 pc with maximum at ∼200 pc, in the middle of our aggregates range, and an indication of a peak at ∼400 pc (complexes). Similar were the findings for LMC (Livanou et al 2007) and NGC 6822 (Karampelas et al 2009), where star complexes were detected in two ranges, from 150-400 pc, so roughly what we considered as aggregates. The second was 400-800 pc, in the complexes range.…”

Section: Comparison With Previous Investigationssupporting

confidence: 88%

“…We compared our results with those derived in a number of studies of other galaxies, M101 and LMC (B98, Kennicut, Stetson 1996, BKS), LMC (Gouliermis et al 2003), M33, M31, SMC (Battinelli et al 1996), NGC 6822 (Karampelas et al 2009;Gouliermis et al 2010), and HST galaxies .…”

Section: Comparison With Previous Investigationsmentioning

confidence: 93%

“…Hierarchical structure (Elmegreen & Efremov 1996;Maragoudaki et al 2001;Livanou et al 2006;Karampelas et al 2009) is indicated in all six galaxies. Most of the associations and aggregates,which are small in size (about 65 pc and 160 pc respectively) and dense, are found to be lying inside the lagrer in size groups, complexes, and supercomplexes (about 500 pc and 1400 pc respectively), which also present the lower density values of all groups, as we can see in Figs.…”

Section: Comparison With Previous Investigationsmentioning

confidence: 99%

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Star forming regions in a sample of HST spiral galaxies

Drazinos

Kontizas

Karampelas

et al. 2013

A&A

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Aims. The presence of small-and large-scale star formation structures in a sample of six spiral Hubble Space Telescope (HST) galaxies is investigated to identify small structures of young stars known as OB associations and to tell whether they are formed inside larger scale star forming stellar structures in a hierarchical form. Methods. This process was based on a friend-of-friend (FOF) algorithm applied to the bright, early type stars above a certain color cutoff limit in order to ensure that we include main sequence stars. A size criterion was introduced in order to apply the same algorithm to different types of stellar structures. Depending on their size, the structures were divided into the four categories of associations, aggregates, complexes, and supercomplexes. Results. Star forming structures of the four types mentioned above are found in all six galaxies of our sample. The majority of the associations and aggregates (the smaller structures) found are lying inside larger structures like complexes and supercomplexes, indicating a hierarchical star formation mechanism.

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Section: Comparison With Previous Investigationssupporting

confidence: 88%

Section: Comparison With Previous Investigationsmentioning

confidence: 93%

Section: Comparison With Previous Investigationsmentioning

confidence: 99%

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Star forming regions in a sample of HST spiral galaxies

Drazinos

Kontizas

Karampelas

et al. 2013

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“…A barlike structure traced by younger stars in Gouliermis et al (2010) cannot be distinguished in the C/M ratio distribution. The area investigated by Karampelas et al (2009) corresponds to the field of Fig. 14. Beyond that, the density of stars is too low and it is difficult to estimate the C/M ratio.…”

Section: C/m Ratio and Metallicity Distributionmentioning

confidence: 99%

Spectra probing the number ratio of C- to M-type AGB stars in the NGC 6822 galaxy

Kacharov

Rejkuba²,

Cioni

2012

A&A

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Aims. We calibrate spectroscopically the C-versus (vs.) M-type asymptotic giant branch (AGB) star selection made using near-IR photometry, and investigate the spatial distribution of the C/M ratio in NGC 6822, based on low resolution spectroscopy and near-IR photometry. Methods. We obtained low resolution multi-object spectroscopy with the VIMOS instrument at the ESO VLT of ∼800 stars in seven fields centred on NGC 6822. The spectroscopic classification of giant stars in NGC 6822 and foreground dwarf contaminants was made by comparing more than 500 good quality spectra with the spectroscopic atlas of Turnshek et al. (1985). The sample of spectroscopically confirmed AGB stars in NGC 6822 is divided into C-and M-rich giants to constrain the C vs. M AGB star selection criteria based on photometry. The larger near-IR photometric sample is then used to investigate the C/M ratio gradients across the galaxy.Results. We present the largest catalogue of near-IR photometry and spectra of AGB stars in NGC 6822 with 150 C-stars and 122 M-stars. Seventy-nine percent of the C-stars in our catalogue are redder than (J − K) 0 = 1.2 mag, and 12% are brighter than K 0 = 16.45 mag and bluer than (J − K) 0 = 1.2 mag. The remaining 9% are mixed with the M-type AGB stars, 88% of which have colours (J − H) 0 > 0.73 mag and (J − K) 0 between 0.9 mag and 1.2 mag. The remainder are mixed with dwarfs and C-type stars. The foreground dwarfs have preferably colours (J − H) 0 < 0.73 mag (95%). Using the proposed criteria, we estimate that the overall C/M ratio of the galaxy is around 0.8 with a spread between 0.2 < C/M < 1.8. These results suggest that the metallicity index [Fe/H] is between −1.2 dex and −1.3 dex according to the different calibrations and that there is a significant spread of about 0.4 ÷ 0.6 dex. We also discuss age rather than metallicity variations that could explain the C/M ratio trends.

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“…The star-count methodology is well known and has been used by several researchers (e.g., Lada & Lada 1995;Carpenter et al 1995Carpenter et al , 2000Kumar et al 2004Kumar et al , 2006. The method can be refined by using different bin sizes in order to investigate large-scale structures, as well as smaller scale subclustering (e.g., Kumar et al 2004;Kirsanova et al 2008), and/or also by smoothing the binned data over adjacent bins (e.g., Karampelas et al 2009). …”

Section: Star Cluster Candidate Finding Methodsmentioning

confidence: 99%

Hundreds of new cluster candidates in the VISTA Variables in the Vía Láctea survey DR1

Barbá

Roman-Lopes

Castellón

et al. 2015

A&A

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Context. VISTA variables in the Vía Láctea is an ESO Public survey dedicated to scanning the bulge and an adjacent portion of the Galactic disk in the fourth quadrant using the VISTA telescope and its near-infrared camera VIRCAM. One of the leading goals of the VVV survey is to contribute to knowledge of the star cluster population of the Milky Way. Aims. To improve the census of Galactic star clusters, we performed a systematic and careful scan of the JHK s images of the Galactic plane section of the VVV survey. Methods. Our detection procedure is based on a combination of stellar density maps and visual inspection of promising features in the J-, H-, and K S -band images. The material examined are VVV JHK S color-composite images corresponding to Data Release 1 of VVV. Results. We report the discovery of 493 new infrared star cluster candidates. The analysis of the spatial distribution show that the clusters are very concentrated in the Galactic plane, presenting some local maxima around the position of large star-forming complexes, such as G305, RCW 95, and RCW 106. The vast majority of the new star cluster candidates are quite compact and generally surrounded by bright and/or dark nebulosities. IRAS point sources are associated with 59% of the sample, while 88% are associated with MSX point sources. GLIMPSE 8 μm images of the cluster candidates show a variety of morphologies, with 292 clusters dominated by knotty sources, while 361 clusters show some kind of nebulosity in this wavelength regime. Spatial crosscorrelation with young stellar objects, masers, and extended green-object catalogs suggest that a large sample of the new cluster candidates are extremely young. In particular, 104 star clusters associated with methanol masers are excellent candidates for ongoing massive star formation. Also, there is a special set of sixteen cluster candidates that present clear signposts of star-forming activity having associated simultaneosly dark nebulae, young stellar objects, extended green objects, and masers.

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Star complexes and stellar populations in NGC 6822

Cited by 15 publications

References 27 publications

Star forming regions in a sample of HST spiral galaxies

Star forming regions in a sample of HST spiral galaxies

Spectra probing the number ratio of C- to M-type AGB stars in the NGC 6822 galaxy

Hundreds of new cluster candidates in the VISTA Variables in the Vía Láctea survey DR1

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