SIMBAD references

2007ApJS..173....1L - Astrophys. J., Suppl. Ser., 173, 1-36 (2007/November-0)

The intrinsically x-ray-weak quasar PHL 1811. II. Optical and UV spectra and Analysis.


Abstract (from CDS):

This is the second of two papers reporting observations and analysis of the unusually bright (mb=14.4), luminous (MB=-25.5), nearby (z=0.192) narrow-line quasar PHL 1811. The first paper reported that PHL 1811 is intrinsically X-ray-weak and presented a spectral energy distribution (SED). Here we present HST STIS optical and UV spectra, and ground-based optical spectra. The optical and UV line emission is very unusual. There is no evidence for forbidden or semiforbidden lines. The near-UV spectrum is dominated by very strong Fe II and Fe III, and unusual low-ionization lines such as Na I D and Ca II H and K are observed. High-ionization lines are very weak; C IV has an equivalent width of 6.6 Å, a factor of ∼5 smaller than measured from quasar composite spectra. An unusual feature near 1200 Å can be deblended in terms of Lyα, N V, Si II, and C III* using the blueshifted C IV profile as a template. Photoionization modeling shows that the unusual line emission can be explained qualitatively by the unusually soft SED. Principally, a low gas temperature results in inefficient emission of collisionally excited lines, including the semiforbidden lines generally used as density diagnostics. The emission resembles that of high-density gas; in both cases this is a consequence of inefficient cooling. PHL 1811 is very unusual, but we note that quasar surveys may be biased against finding similar objects.

Abstract Copyright:

Journal keyword(s): Galaxies: Quasars: Emission Lines - quasars: individual (PHL 1811) - X-Rays: Galaxies

CDS comments: RX J2219.9-5941 is a misprint for RX J2217.9-5941, PHL 1181 is a misprint for PHL 1811.

Simbad objects: 23

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