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J/ApJ/705/1533        NGC 5128 globular clusters          (Chattopadhyay+, 2009)

Study of NGC 5128 globular clusters under multivariate statistical paradigm. Chattopadhyay A.K., Chattopadhyay T., Davoust E., Mondal S., Sharina M. <Astrophys. J., 705, 1533-1547 (2009)> =2009ApJ...705.1533C
ADC_Keywords: Clusters, globular ; Galaxies, optical ; Models Keywords: galaxies: general - globular clusters: general - methods: statistical Abstract: An objective classification of the globular clusters (GCs) of NGC 5128 has been carried out by using a model-based approach of cluster analysis. The set of observable parameters includes structural parameters, spectroscopically determined Lick indices and radial velocities from the literature. The optimum set of parameters for this type of analysis is selected through a modified technique of principal component analysis, which differs from the classical one in the sense that it takes into consideration the effects of outliers present in the data. Then a mixture model based approach has been used to classify the GCs into groups. The efficiency of the techniques used is tested through the comparison of the misclassification probabilities with those obtained using the K-means clustering technique. On the basis of the above classification scheme three coherent groups of GCs have been found. We propose that the clusters of one group originated in the original cluster formation event that coincided with the formation of the elliptical galaxy, and that the clusters of the two other groups are of external origin, from tidally stripped dwarf galaxies on random orbits around NGC 5128 for one group, and from an accreted spiral galaxy for the other. Description: In the present study, we have first used a modified technique of principal component analysis (PCA; Salibian-Barrera et al. 2006, J. Am. Stat. Assoc., 101, 1198) to search for the optimum set of parameters which gives the maximum variation for the GCs in NGC 5128. Then we have classified the GCs on the basis of these significant parameters using a model-based method of cluster analysis (CA; Qui, D. & Tamhane, A. C. 2007, J. Stat. Plan. Inference, 137, 3722) which finds the structure of the optimum groups of GCs instead of choosing groups in an ad hoc manner on the basis of a single parameter. Our analysis is based on the sample of GCs of the early-type central giant elliptical galaxy in the Centaurus group, NGC 5128, whose structural parameters have been derived by fitting King and Wilson models to the surface brightness profiles based on HST/ACS imaging in the F606W bandpass (McLaughlin et al. 2008MNRAS.384..563M). File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 82 130 List of parameters of the globular clusters of NGC 5128 used in principal component analysis (PCA) and cluster analysis (CA) table2.dat 76 130 List of parameters as well as derived parameters of the globular clusters of NGC 5128
See also: J/AJ/139/1871 : Kinematics of globulars in NGC 5128 (Woodley+, 2010) J/AJ/140/2101 : NGC 5128 globular clusters photometry (Sinnott+, 2010) J/ApJ/708/1335 : Spectroscopy of globulars in NGC 5128 (Woodley+, 2010) J/ApJ/682/199 : Globulars with X-ray sources in NGC 5128 (Woodley+, 2008) J/MNRAS/386/1443 : 2dF study of globular clusters in NGC 5128 (Beasley+, 2008) J/AJ/134/494 : NGC 5128 globular clusters UBVRICMT1 phot. + RV (Woodley+, 2007) J/AJ/132/2187 : MCT1 photometry of NGC 5128 GCs (Harris+, 2006) J/AJ/128/723 : Washington Photometry in NGC 5128. II (Harris+, 2004) J/AJ/128/712 : Washington Photometry in NGC 5128 (Harris+, 2004) J/ApJS/150/367 : Globular clusters in NGC 5128 (Peng+, 2004) J/A+A/369/812 : UVKs photometry of globular clusters in NGC 5128 (Rejkuba, 2001) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 9 A9 --- Name Globular cluster name (G1) 10 A1 --- f_Name [a] discarded in CA (G2) 12 I1 --- Group [1,3]? Group membership found by CA (G3) 14- 17 F4.2 --- c Concentration (c∼log(Rtid/Rc)) (G1) 19- 23 F5.2 mag/arcsec2 muV V surface brightness averaged over half-light radius (<µv>h) (G1) 25- 29 F5.2 mag/arcsec2 mu0 Extinction-corrected central surface brightness in the F606W bandpass (G1) 31- 35 F5.2 --- W0 Dimensionless central potential of the best-fitting model (G1) 37- 42 F6.3 [pc] logRc Log core radius (G1) 44- 47 F4.2 [pc] logRtid Log tidal radius (G1) 49- 54 F6.3 [pc] logrh Log half-light radius (G1) 56- 59 F4.2 [Msun] logM Integrated model mass (logMtot) (G1) 61- 70 E10.6 Msun/pc3 rho0 Central volume density (G1) 72- 76 F5.2 km/s sig.P Predicted line of sight velocity dispersion at the cluster center (σp,0) (G1) 78- 82 F5.2 10+9yr trh Two-body relaxation time at the model projected half-mass radius (G1)
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 9 A9 --- Name Globular cluster name (G1) 10 A1 --- f_Name [a] discarded in CA (G2) 12 I1 --- Group [1,3]? Group membership found by CA (G3) 14- 18 F5.2 kpc Rgc Galactocentric radius (G1) 20- 24 F5.2 mag T1 Washington T1 magnitude (G1) 26- 30 F5.2 [Sun] [Fe/H] Fe/H abundance (G1) 32- 35 F4.2 mag (C-T1)0 Extinction corrected (C-T1)0 color index (G1) 37- 39 I3 km/s RV ? Weighted mean radial velocity from Woodley et al. (2007, Cat. J/AJ/134/494) 41- 45 F5.2 [Sun] [Z/H] ? Metallicity 46 A1 --- u_[Z/H] [:] Uncertainty flag on [Z/H] (1) 48- 51 F4.2 [Sun] e_[Z/H] ? [Z/H] uncertainty 53- 57 F5.2 Gyr Age ? Age 58 A1 --- u_Age [:] Uncertainty flag on Age (1) 60- 63 F4.2 Gyr e_Age ? Age uncertainty 65- 69 F5.2 km/s Vrot ? Rotational velocity 71- 76 F6.2 km/s sigma ? Velocity dispersion (σV)
Note (1): ":" are used for the errors of [Z/H] and ages when the error of [Z/H]>0.4dex and the error of Age>4Gyr.
Global notes: Note (G1): From McLaughlin et al. (2008MNRAS.384..563M) Note (G2): the globular clusters markedf "a" have not been considered during the cluster analysis (CA) as they are outliers. Note (G3): the cluster analysis (CA) segregated the sample of GCs into three groups, G1, G2, G3, according to their structural properties. The different properties of the three groups are presented in Table 4 of the paper. The main difference between the groups lies in the mean luminosities (T1) of the GCs and their individual central velocity dispersions (σp,0), which are both indicators of their individual masses. The GCs of G2 are the most massive, followed by those of G1, and then G3. Main characteristics for the 3 groups are: * G1 (47 GCs): T1=19.462±0.081mag ; σp,0=9.984±0.400km/s * G2 (35 GCs): T1=18.218±0.159mag ; σp,0=20.528±1.130km/s * G3 (45 GCS): T1=21.156±0.092mag ; σp,0=3.533±0.144km/s
History: From electronic version of the journal
(End) Emmanuelle Perret [CDS] 07-Dec-2011
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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