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11.4. Quasars and the Sunyaev-Zel'dovich effects

The intergalactic medium near a quasar must be strongly ionized by the quasar's radiation. These hot gas bubbles are likely to be overpressured, and to expand into their surrounding intergalactic medium. Thus both thermal and kinematic Sunyaev-Zel'dovich effects may arise near quasars, and we might expect a contribution from quasars in the spectrum of fluctuations in the CMBR (Aghanim et al. 1996). Aghanim et al. find that the kinematic effect dominates, and can cause local changes of approx 300 µK in the brightness temperature of the CMBR on scales up to approx 1 deg. Whether such structures are indeed present in the CMBR will be tested by the next generation of CMBR surveys.

Sunyaev-Zel'dovich effects may also be seen from the Lyman alpha absorption clouds seen in quasar spectra (Loeb 1996). The expected effects are much smaller, typically only a few µK and with angular sizes of less than an arcminute, from the varying numbers of Lyalpha systems on different lines of sight. Here again the dominant contribution to the signal is from the kinematic Sunyaev-Zel'dovich effect, and relies on large velocities acquired by the Lyalpha absorbing clouds as large-scale structure forms.

Either of these effects, or possibly a Sunyaev-Zel'dovich effect from a quasar-related cluster with a deficiency of bright galaxies, or a kinematic effect from colliding QSO winds (Natarajan & Sigurdsson 1997), might explain the observations of CMBR anisotropies towards the quasars PHL 957 (Andernach et al. 1986) and PC 1643+4631 (Jones et al. 1997). However, the reality of these detections remains in some dispute until they are independently confirmed.