Differences between the optical/ultraviolet spectra of X-ray bright and X-ray faint QSOs

作者：Green PJ^*

来源：Astrophysical Journal, 1998, 498(1): 170-180.

DOI：10.1086/305537

• galaxies, active
• quasars, emission lines
• quasars, general
• ultraviolet, galaxies
• X-rays, galaxies

We contrast measurements of composite optical and ultraviolet (UV) spectra constructed from samples of QSOs defined by their soft X-ray brightness. X-ray bright (XB) composites show stronger emission lines in general, but particularly from the narrow-line region. The difference in the [O III]/H beta ratio is particularly striking, and is even more so when blended Fe II emission is properly subtracted. The correlation of this ratio with X-ray brightness was a principal component of QSO spectral diversity found by Boroson & Green. We find here that other, much weaker narrow optical forbidden lines ([O II] and [Ne v]) are enhanced by factors of 2 to 3 in our XB composites, and that narrow line emission is also strongly enhanced in the XB UV composite. Broad permitted-line fluxes are slightly larger for all XB spectra, but the narrow-/broad-line ratio stays similar or increases strongly with X-ray brightness for all strong permitted lines except H beta.
Spectral differences between samples divided by their relative X-ray brightness las measured by alpha(ox)) exceed those seen between complementary samples divided by luminosity or radio loudness. We propose that the Baldwin effect may be a secondary correlation to the primary relationship between alpha(ox) and emission line equivalent width. We conclude that either (1) W-lambda depends primarily on the shape of the ionizing continuum, as crudely characterized here by alpha(ox), or (2) both W-lambda and alpha(ox) are related to some third parameter characterizing the QSO physics. One such possibility is intrinsic warm absorption; a soft X-ray absorber situated between the broad and narrow line regions can successfully account for many of the properties observed.

• 出版日期1998-5-1