A New Automated Classification Technique of Galaxy Spectra with Z0.5[5]. Therefore, we try to develop a new automated classification method of galaxy spectra with unknown redshift. Such a method once developed can be of great help for automated redshift measurement since at this stage, the belong’s class of a spectrum is known. Galaxies are basically composed of two main classes, normal galaxies (NGs) and active galaxies (AGs). Spectra of NGs generally have absorption lines, while those of AGs have emission lines. However, the galaxy spectra with high redshift *
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[email protected]; National Pattern Recognition Laboratory of Automation Institute, Chinese Academy of Sciences, Beijing, China 100080; **
[email protected] ; National Astronomical Observatories, Chinese Academy of Sciences, Beijing, China 100012
do not possess such features. This paper is concentrated to distinguish NGs from AGs, with redshift value being less than 1.2. The classification of subclasses will be in our future work. In this paper, we investigate PCA-ODP approach for the classification of NGs from AGs on the data set of galaxies with z from 0 to 1.2. The approach consists of the following two main steps: at first, the Principal Components Analysis (PCA) is employed to extract features of galaxy spectra; then Optimal Discrimination Plane (ODP) is used in the feature space to classify galaxies.
2. DATA The templates, from which our data set was simulated, include the spectra atlas of quiescent and starburst galaxies discussed by Kinney et al. (1996)[6][7]. The galaxy spectra of the Atlas of Kinney et al. (1996) cover the ultraviolet to near-infrared spectral range, i.e. from 1200 up to 10 000 Å. The UV spectra have been obtained with the large aperture (10" by 20") and low- resolution spectrographs of the IUE satellite. The optical spectra were obtained through a long slit with a 10" width, subsequently a window 20" long was extracted to match the 10"
20" IUE aperture. The former
cover the wavelength range of 1200-3200 Å, with a resolution of ~6 Å. The latter cover the range of 3200-10 000 Å, with a resolution of ~8 Å. The internal extinction of all the spectra was corrected. The quiescent galaxies were grouped according to morphological type: E, S0, Sa, Sb, and Sc, respectively. The spectra of starburst galaxies were grouped according to increasing values of the color excess E(B-V): from SB1, with E(B-V)
