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Understanding the properties and diversity of Galaxies and Quasars through Spectral Decomposition

Yip, Ching-Wa (2005) Understanding the properties and diversity of Galaxies and Quasars through Spectral Decomposition. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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In the first part of this thesis, we study spectral decompositions of galaxies and quasars (QSOs) by the Karhunen-Lo`eve (KL) transformusing the Sloan Digital Sky Survey (SDSS). Our goal is to understand the average properties and sample variances of the data, with an eyetoward 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 firstthree eigencoefficients of each spectrum. Spectral types, corresponding to different Hubble-types and galaxies with extremeemission lines, are identified for 170,000 spectra and are shown to be complementary to existing spectral classifications. Biasin 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 angstrom) 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) usingmulti-epoch observations in the SDSS. We study the galaxy variability per spectral type defined previously in the KL transform and in theOsterbrock diagram. The amplitude of galaxy variability is found to depend on spectral type. We show that the variability in theHII 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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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairConnolly, Andrew
Committee MemberSzalay, Alex
Committee MemberTurnshek, David Aturnshek@quasar.phyast.pitt.eduTURNSHEK
Committee MemberSheth, Ravi
Committee MemberWu,
Date: 10 October 2005
Date Type: Completion
Defense Date: 5 August 2005
Approval Date: 10 October 2005
Submission Date: 11 August 2005
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Institution: University of Pittsburgh
Schools and Programs: Dietrich School of Arts and Sciences > Physics
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: classification; data mining; Principal Component Analysis; spectral variability; spectroscopy
Other ID:, etd-08112005-141622
Date Deposited: 10 Nov 2011 19:59
Last Modified: 15 Nov 2016 13:48


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