Based on observations collected at the European Southern Observatory, Cerro Paranal, Chile (ESO 267.A-5698).

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Research Associate FNRS (Belgium).

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... de-excitation

In principle, excitation by infrared radiation is also possible. However, for this excitation mechanism to be significant, very low electron densities are required, hence extremely large distances of the low-ionization clouds from the photoionization source. Even if the infrared source is extended, this requires infrared flux densities much larger than expected for a typical quasar, and SDSS J0011+0055, undetected by IRAS, is not an infrared-luminous quasar.

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...2001)

Note that 3C 191 is a radio-loud quasar, whereas SDSS J0011+0055 is radio-quiet by virtue of its non-detection in the FIRST survey (Becker et al. 1995). Absorbers apparently can be found at large distances from the ionizing source in both RLQs and RQQs.

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