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The PG X-ray QSO sample: Links between the UV-X-ray Continuum and Emission Lines

Beverley J. Wills·M. S. Brotherton·A. Laor·D. Wills·B. J. Wilkes·G. J. Ferland·Zhaohui Shang
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Abstract

The UV to soft X-rays of luminous AGNs dominate their bolometric luminosity, driven by an accretion-powered dynamo at the center. These photons ionize the surrounding gas, thereby providing clues to fueling and exhaust. Two sets of important relationships - neither of them understood - link the continuum and gas properties. (i) Boroson & Green's `eigenvector 1' relationships: Steeper soft X-ray spectra are clearly related to narrower Hbeta emission and stronger optical Fe II emission from the BLR, and weaker [O III] 5007 from the NLR. We show that these relationships extend to UV spectra: narrower C III] 1909, stronger low ionization lines, larger Si III] 1892/C III] 1909 (a density indicator), weaker C IV 1549 but stronger higher-ionization N V 1240. We speculate that high accretion rates are linked to high columns of dense (1e10 - 1e11 cm-3), nitrogen-enhanced, low-ionization gas from nuclear starbursts. Linewidth, inverse Fe II-[O III] and inverse Fe II-C IV relationships hint at the geometrical arrangement of this gas. (ii) The Baldwin effect (inverse equivalent width - luminosity relationships): Our correlation analyses suggest that these are independent of the above eigenvector 1 relationships. The eigenvector 1 relationships can therefore be used in future work, to reduce scatter in the Baldwin relationships, perhaps fulfilling the dream of using the Baldwin effect for cosmological studies.

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Beverley J. Wills, M. S. Brotherton, A. Laor, D. Wills, B. J. Wilkes, G. J. Ferland, Zhaohui Shang. 1999-05-07. The PG X-ray QSO sample: Links between the UV-X-ray Continuum and Emission Lines. https://arxiv.org/abs/astro-ph/9905091

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