Understanding the properties and diversity of galaxies and quasars through spectral decomposition

Details Understanding the properties and diversity of galaxies and quasars through spectral decomposition Understanding the properties and diversity of galaxies and quasars through spectral decomposition

Nov 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005phdt.........4y&link_type=abstract

Ph.D dissertation, 2005. Section 0178, Part 0606 187 pages; United States -- Pennsylvania: University of Pittsburgh; 2005. Publ

Computer Science

Galaxies, Quasars

Scientific paper

In the first part of this thesis, we study spectral decompositions of galaxies and quasars (QSOs) by the Karhunen-Loeve (KL) transform using the Sloan Digital Sky Survey (SDSS). Our goal is to understand the average properties and sample variances of the data, with an eye toward obtaining objective classifications of these objects.
The eigencoefficients describing the 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 ~ 170, 000 spectra and are shown to be complementary to existing spectral classifications. Bias in the spectral classifications due to the aperture spectroscopy in the SDSS is within the signal-to-noise limit for majority of galaxies.
We extend the analysis to the decomposition of ~ 17, 000 QSO spectra in which the diversity is known to be larger. From a commonality analysis on the eigenspectra sets constructed using different QSO samples, we deduce that QSO spectral classification is redshift and luminosity dependent. The prominent redshift effect is found to be the evolution of the small bump. The luminosity effect is related to the Baldwin effect. We therefore perform the KL transforms in three cases: the local (in the vicinity of emission lines), the intermediate (redshift and luminosity binned) and the global (restframe 900-8000 Å) spectral bandpasses. We find that the second order QSO eigenspectra, in both the global and the intermediate spectral bandpasses, represent features from the host galaxies of the QSOs. We discuss the insights the results provide toward classification.
In the second part of this thesis, we probe spectroscopic variability of galaxies and narrow line active galactic nuclei (AGNs) using multi-epoch observations in the SDSS. We study the galaxy variability per spectral type defined previously in the KL transform and in the Osterbrock diagram. The amplitude of galaxy variability is found to depend on spectral type. We show that the variability in the H II galaxies can be partly due to star formation; and that in the AGNs and the mean eClass type D are probably not related to starbursts.

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