The Baldwin Effect and Black Hole Accretion: A Spectral Principal Component Analysis of a Complete Quasar Sample

Abstract

We have performed a spectral principal component analysis (SPCA) for an essentially complete sample of 22 low redshift QSOs with spectral data from Lyα to Hα. SPCA yields a set of independent principal component spectra, each of which represents a set of relationships among QSO continuum and line properties. We find three significant principal components, which account for ∼78% of the total intrinsic variance. The first component, carrying ∼41% of the intrinsic variance, represents Baldwin relationships -anti-correlations between equivalent width of broad emission lines and continuum luminosity. The narrow line core (FWHM ∼2000 km s −1 ) of the broad emission lines dominate this component. The second component, accounting for ∼23% of the intrinsic variance, represents the variations in UV continuum slope, which is probably the result of dust reddening, with possible contributions from starlight. The third principal component is directly related to the Boroson & Green "Eigenvector 1" (their first principal component), clearly showing the anti-correlation between strengths of optical Fe ii and [O iii] λ5007, and other relationships previously found in the Hβ -[O iii] region. This third component shows the expected strong correlation with soft X-ray spectral index. The widths of C iii] λ1909, Mg ii λ2798, and Balmer emission lines are also involved and clearly correlated, relating this component to black hole mass or Eddington accretion ratio. We find an inverse correlation between the strengths of the UV and optical Fe ii blends, as suggested by some photoionization models. We also find correlations of the strengths of several low-ionization UV lines with Fe ii(opt), and a strong positive correlation of C iv λ1549 with [O iii] strength. The wide wavelength coverage of our data enable us to see clearly the relationships between the UV and optical spectra of QSOs. The Baldwin effect and Boroson & Green's Eigenvector 1 relationship are clearly independent. We demonstrate how Baldwin relationships can be derived using our first principal component, virtually eliminating the scatter caused by the third principal component. This rekindles the hope that the Baldwin relationships can be used for cosmological study.

How similar are the properties of quasars with nearly identical ultraviolet spectra?

“…Figure 5 plots the first two SPCs, which together account for 48.8% of the variance. SPC1 has emission lines narrower than the mean spectrum, and is roughly consistent with both the SPC1s of Francis et al (1992) and Shang et al (2003), and the Intermediate Line Region (ILR) spectrum of Brotherton et al (1994) (see also Pâris et al 2011). SPC2 is dominated by continuum variation suggestive of dust reddening, along with some associated emissionline variation.…”

Dependence of equivalent width of quasar emission lines on UV-optical spectral index

“…We also did not see any Baldwin effect for this set of lines, although it was found by Shang et al (2003) for Oi line.…”

“…Continuum and emission lines are believed to originate from the hot accretion disc and circumnuclear fast moving clumps, correspondingly. The proximity of these regions is considered to be the most promising explanation of the Baldwin (1977) effect: the inverse correlation of EW of some emission lines with the monochromatic luminosities at UV region, e. g., for Lyα (1215Å), Siii (1260Å), Oi (1304Å), Siiv+Oiv] (1400Å) lines (see e. g. Dietrich et al 2002, Green, Forster & Kuraszkiewicz 2001, and Shang et al 2003. But the physical explanation of the difference in α λ and relation of quasar luminosity and lines' EW to α λ are still not clear.…”

Emission Line Properties of Active Galactic Nuclei from a Post‐COSTARHubble Space TelescopeFaint Object Spectrograph Spectral Atlas

“…This set of correlations was found to be the primary eigenvector of the emission line correlation matrix of PG quasars studied by Boroson & Green (1992). This eigenvector 1 was later found to correlate with UV properties such as C iv shift/asymmetry (Marziani et al 1996), Si iii]/C iii] ratio, and C iv and N v strength (Wills et al 1999;Shang et al 2003). Since eigenvector 1 was found to correlate significantly with X-ray properties (Laor et al 1997;Brandt & Boller 1998), which are determined in the vicinity of the central black hole, it was suggested that differences in emission line properties revealed by eigenvector 1 are caused by differing central engine parameters (e.g., L/L Edd , accretion rate, orientation, and/ or black hole spin).…”

“…In reality, the scatter of the Baldwin effect is too large to give meaningful results, and studies have concentrated on understanding and reducing this scatter (Shang et al 2003;Dietrich et al 2002). Conflicting results have also emerged, where radio-loud samples and samples with a wide range of luminosities show a stronger effect (e.g., Baldwin et al 1978;Wampler et al 1984;Kinney, Rivolo, & Koratkar 1990;Wang, Lu, & Zhou 1998), while radio-quiet samples and samples with a small luminosity range show weaker or no effect (e.g., Steidel & Sargent 1991;Wilkes et al 1999).…”