Distributions of Galaxy Spectral Types in the Sloan Digital Sky Survey

By C. Yip, A. Connolly, A. Szalay, Tamás Budavári, Mark SubbaRao, Joshua A. Frieman, R. Nichol, Andrew M. Hopkins, Donald G. York, S. Okamura and 5 more. 2004

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We 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.

Subfields: Analytical Chemistry, Astronomy and Astrophysics, Ecology

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Citations in the corpus

Bursty stellar populations and obscured active galactic nuclei in galaxy bulges (2007, methodology): “As nebular emission varies greatly between galaxies, any PCA on a representative population of galaxy spectra primarily describes the emission-line strength (Madgwick et al. 2003; Yip et al. 2004), which quantifies current SFR and/or AGN strength alone.”
SDSS DR7 WHITE DWARF CATALOG (2012, methodology): “We removed the known quasars (Schneider et al. 2010), BL Lac objects (Plotkin et al. 2010), and once we had run through our DA and DB model-ﬁtting program, we ﬁt the rejects with galaxy and quasar templates (Yip et al. 2004a, 2004b) to remove these objects from further consideration.”
The Mass Function of Active Black Holes in the Local Universe (2007, methodology): “The stellar continuum shape is provided by the eigenspectra presentd i Yip et al. (2004).”
The Coevolution of Galaxies and Supermassive Black Holes: Insights from Surveys of the Contemporary Universe (2014, methodology): “More examples of the use of PCA and other sophisticated techniques for extraction of information about the stellar content and star-formation history from the SDSS galaxy spectra include Panter et al. (2003, 2007), Cid Fernandes et al. (2005), and Yip et al. (2004).”
Photometric redshifts for the SDSS Data Release 12 (2016, background): “Alternatively, sets of measured galaxy spectra can be used to compile a library of empirical spectral templates, where the inclusion of measured lines is relatively straightforward (Yip et al. 2004; Dobos et al. 2012; Marchetti et al. 2013).”
Soft X-Ray and Ultraviolet Emission Relations in Optically Selected AGN Samples (2005, methodology): “The host galaxy and AGN components were created using the first 3–20 galaxy and AGN eigenspectra obtained from large SDSS samples by Yip et al. (2004a, 2004b).”
The Luminosity Function and Star Formation Rate between Redshifts of 0.07 and 1.47 for Narrowband Emitters in the Subaru Deep Field (2006, methodology): “NB Excess Predictions from Sloan Digital Sky Survey Mean spectra for six galaxy types (from early to late) were obtained from Yip et al. (2004) and were then redshifted for either Hα, [O iii], or [O ii] to fall within the four NB filters and then convolved with the BB and NB filters.”
Spectral Classification of Quasars in the Sloan Digital Sky Survey: Eigenspectra, Redshift, and Luminosity Effects (2004, methodology): “Second Global Eigenspectrum: Host-Galaxy Component The second eigenspectrum shows a striking similarity in the optical region (krest 3500 8) with the first galaxy eigenspectrum (i.e., mean spectrum) from the SDSS galaxies (of 170,000 galaxy spectra; Yip et al. 2004).”
Active Galactic Nuclei in the Sloan Digital Sky Survey. I. Sample Selection (2005, methodology): “In this paper the library is constructed by applying the principal component analysis (PCA) technique (e.g., Connolly et al. 1995; Lahav et al. 1996; Bromley et al. 1998; Eisenstein et al. 2003; Yip et al. 2004) to a sample of pure absorption-line galaxies.”