86 research outputs found
Introduction to Principal Components Analysis
Understanding the inverse equivalent width - luminosity relationship (Baldwin
Effect), the topic of this meeting, requires extracting information on
continuum and emission line parameters from samples of AGN. We wish to discover
whether, and how, different subsets of measured parameters may correlate with
each other. This general problem is the domain of Principal Components Analysis
(PCA). We discuss the purpose, principles, and the interpretation of PCA, using
some examples from QSO spectroscopy. The hope is that identification of
relationships among subsets of correlated variables may lead to new physical
insight.Comment: Invited review to appear in ``Quasars and Cosmology'', A.S.P.
Conference Series 1999. eds. G. J. Ferland, J. A. Baldwin, (San Francisco:
ASP). 10 pages, 2 figure
Spectral Properties From Lyman-alpha to H-alpha For An Essentially Complete Sample of Quasars I: Data
We have obtained quasi-simultaneous ultraviolet-optical spectra for 22 out of
23 quasars in the complete PG-X-ray sample with redshift, z<0.4, and M_B<-23.
The spectra cover rest-frame wavelengths from at least Lyman-alpha to H-alpha.
Here we provide a detailed description of the data, including careful
spectrophotometry and redshift determination. We also present direct
measurements of the continua, strong emission lines and features, including
Lyman-alpha, SiIV+OIV], CIV, CIII], SiIII], MgII, H-beta, [OIII],
He5876+NaI5890,5896, H-alpha, and blended iron emission in the UV and optical.
The widths, asymmetries and velocity shifts of profiles of strong emission
lines show that CIV and Lyman-alpha are very different from H-beta and H-alpha.
This suggests that the motion of the broad line region is related to the
ionization structure, but the data appears not agree with the radially
stratified ionization structure supported by reverberation mapping studies, and
therefore suggest that outflows contribute additional velocity components to
the broad emission line profiles.Comment: 42 pages, 10 figures, 13 tables. Accepted by AJ. Supplemental figures
not included. Full version available at
http://physics.uwyo.edu/~shang/pgxpaper/ShangPaper.pd
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