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Abstract
Subjective classification of spiral galaxies is not sufficient for studying the effect of bars on their physical characteristics. In reality the problem is to comprehend the complex correlations in a multivariate parametric space. Multivariate tools are the best ones for understanding this complex correlation. In this work an objective classification of a large set (26,089) of spiral galaxies was compiled as a value added galaxy catalogue from sdss DR 15 virtual data archive. Initially for dimensionality reduction, Independent Component Analysis is performed to determine a set of Independent Components that are linear combinations of 48 observed features (namely ionized lines, Lick indices, photometric and morphological properties). Subsequently a K-means cluster analysis is carried out on the basis of the 14 best chosen Independent Components to obtain 12 distinct homogeneous groups of spiral galaxies. Amongst these, 3 groups are the oldest ones (1.6 Gyr − 5.9 Gyr), while 5 groups fall in the medium aged category (1.4 Gyr − 1.6 Gyr), 2 groups consist of only unbarred spirals, 1 group is the youngest one and the remaining one is an outlier. In many groups there are clear indication of recurrent bar formation phenomena which is consistent with few previous simulation works. In order to study the robustness of the clusters with respect to the method of clustering, a second method of clustering by Gaussian Mixture Modeling Method (GMMBC) is applied.
Acknowledgement
The authors are grateful to the sdss Data Release 15 (sdss DR15)Footnote8 for giving the opportunity to retrieve the data and to work with it. One of the authors Prasenjit Banerjee acknowledges to a research fellowship provided by The University Grants Commission, with UGC Id. NOV2017-422665 & UGC Reference No. 1141/(CSIR-UGC Net June 2017).