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2.5.3. Small scale anisotropy

On angular scales less than 90°, the search for anisotropy has almost invariably resulted in upper limits on possible temperature fluctuations. Discouraging though this is, the limits on deltaT / T have imposed severe Constraints on theories of galaxy formation. One of the most significant upper limits is actually reported as a positive result

Equation 2.37 (2.37)

at an angular scale of 6° by Fabbri et al. (1982), but is conservatively taken as an upper limit of 4 × 10-5. This is because the measurement, performed with a broadband detector in the far infrared (0.05-3 mm) wavelength range, may be affected to an indeterminate extent by galactic emission. Other experiments using radiometric techniques in the wavelength range 0.35-11 cm, have imposed upper limits over angular scales from 1' to 2°. Another important result is the limit deltaT / T < 3 × 10-5 over angular scales from 10° to 90° (Fixsen et al. 1983). A selection of the most sensitive recent limits, as corrected by Partridge (1980a, b) together with the detections of anisotropy over large angular scales, is summarized in Table 2.1. In Section 4, we shall compare these limits with the predictions of galaxy formation theory.

Table 2.1. Selected observations of and limits on CBR anisotropy
Observers lambda(cm) theta DeltaT/T
Pigg 1 2.0 1.3' ltapprox 4 × 10-4
Birkinshaw 2 3.0 4.5' ltapprox 4 × 10-4
Partridge 3 0.4 7' ltapprox 2 × 10-4
Parijskij el al. 4 4.0 5'-150' < 4 × 10-4 to
      ltapprox 7.5 × 10-5
Caderni et al. 5 0.13 30' ltapprox 1.2 × 10-4
Smoot and Lubin 6 0.91 7°-20° ltapprox 3 × 10-4
    180° 1.1 ( ± 0.1) × 10-3
Boughn et al. 7 0.05-0.3 180° 1.3 ( ± 0.1) × 10-3
Fabbri et al. 8 0.05-0.3 180° 1.0 ( ± 0.3) × 10-3
    90° 3 ( ± 1) × 10-4
Melchiorri et al. 9 0.07 6° < 4.4 × 10-5
Fixsen et al. 10 1.2 10°-90° < 3 × 10-5
Lubin et al. 11 0.3 90° < 6.2 × 10-5
1. Pigg, J.C. Unpublished, quoted by Partridge (1980a).
2. Birkinshaw (1980).
3. Partridge (1980b).
4. Parijskij, Petrov and Cherkov (1977) corrected by Partridge (1980a).
5. Caderni et al. (1977).
6. Smoot and Lubin (1979).
7. Boughn, Cheng and Wilkinson (1981).
8. Fabbri et al. (1980).
9. Melchiorri et al. (1981).
10. Fixsen, Cheng and Wilkinson (1983).
11. Lubin, Epstein and Smoot (1983).

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