C. W. Yip et al. 2004 The Astronomical Journal 128 585 doi:10.1086/422429
C. W. Yip1, A. J. Connolly1, A. S. Szalay2, T. Budavári2, M. SubbaRao3, J. A. Frieman3, R. C. Nichol4, A. M. Hopkins1, D. G. York3,5, S. Okamura6, J. Brinkmann7, I. Csabai2,8, A. R. Thakar2, M. Fukugita9 and Ž. Ivezić10
Show affiliationsWe perform an objective classification of 170,000 galaxy spectra in the Sloan Digital Sky Survey (SDSS) using the Karhunen-Loève (KL) transform. With about one-sixth of the total set of galaxy spectra that will be obtained by the survey, we are able to carry out the most extensive analysis of its kind to date. The formalism proposed by Connolly and Szalay is adopted to correct for gappy regions in the spectra and to derive eigenspectra and eigencoefficients. From this analysis, we show that this gap-correction formalism leads to a converging set of eigenspectra and KL-repaired spectra. Furthermore, KL eigenspectra of galaxies are found to be convergent not only as a function of iteration, but also as a function of the number of randomly selected galaxy spectra used in the analysis. From these data a set of 10 eigenspectra of galaxy spectra are constructed, with rest-wavelength coverage 3450–8350 Å. The eigencoefficients describing these galaxies naturally place the spectra into several classes defined by the plane formed by the first three eigencoefficients of each spectrum. Spectral types corresponding to different Hubble types and galaxies with extreme emission lines are identified for the 170,000 spectra and are shown to be complementary to existing spectral classifications. From a nonparametric classification technique, we find that the population of galaxies can be divided into three classes that correspond to early late-type through intermediate late-type galaxies. This finding is believed to be related to the color separation of SDSS galaxies discussed in earlier works. Bias in the spectral classifications due to the aperture spectroscopy in the SDSS is small and within the signal-to-noise limit for a majority of galaxies, except for the reddest nearby galaxies and large galaxies (>30 kpc) with prominent emissions. The mean spectra and eigenspectra derived from this work can be downloaded from the SDSS Web site.
galaxies: fundamental parameters; galaxies: general; methods: data analysis; techniques: spectroscopic
Issue 2 (2004 August)
Received 2003 May 12, accepted for publication 2004 May 6
C. W. Yip et al. 2004 The Astronomical Journal 128 585
Donald P. Schneider et al. 2002 The Astronomical Journal 123 567
Donald P. Schneider et al. 2007 The Astronomical Journal 134 102
Jennifer K. Adelman-McCarthy et al. 2008 ApJS 175 297
Donald P. Schneider et al. 2005 The Astronomical Journal 130 367
Željko Ivezić et al. 2000 The Astronomical Journal 120 963
Kevork N. Abazajian et al. 2009 ApJS 182 543
Gordon T. Richards et al. 2002 The Astronomical Journal 124 1
Daisuke Ida JHEP09(2000)014
Per Kraus JHEP12(1999)011