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Colloquium on the Age of the Universe, Dark Matter, and Structure Formation
FIG. 5. A computer simulation of the expected MAP results after 2 years of operation. The temperature range is ±100 µK. Note the effect of higher angular resolution compared with Fig. 1. MAP’s wide frequency coverage and high angular resolution will be needed to understand contamination by Galactic radio and dust emission.
is the real map from the COBE/DMR instrument. MAP’s 30 times greater resolution is due to the larger apertures of its back-to-back telescopes (see Fig. 4), and its HEMT amplifier technology developed at the National Radio Astronomy Observatory (35) is 50 times more sensitivity than the mixer-based radiometers used in the COBE/DMR. MAP measures the CMBR anisotropy in 5 frequency bands from 20 to 106 GHz to separate foreground microwave sources from the spectrally unique CMBR anisotropy. Because of its differential design and beam size, MAP’s, angular power spectrum will cover the range 2=l=800. The COBE/DMR measurement will be repeated to establish the large-scale baseline, and at least two of the predicted peaks of the angular power spectrum will be measured, if they exist. PLANCK, scheduled to launch 5 years after MAP, will be able to resolve more peaks and get better data on the expected damping at small angles. Hu and White (36; also see the Hu Web site, http://www.sns.ias.edu/~whu/physics/physics.html) show simulated power spectrum results for both satellites, and several theoretical groups have estimated the accuracy to which successful MAP and PLANCK missions can measure important cosmological parameters (11, 12). However, these should be regarded as a rough indication of the potential of these satellites. Much will depend on whether the underlying cosmological model can be independently established from the CMBR anisotropy data or from other methods. Parameter values will depend strongly on the model used, and accuracy of the parameter estimates will depend on the parameter correlations within that model.
Current active development of close-packed interferometers is directed at measuring small-scale CMBR anisotropy (interferometers are being developed at the Mullard Radio Observatory, the California Institute of Technology, and the University of Chicago). The resolution of these instruments will overlap the angular scales measured by the satellites, and they will extend the angular power spectrum down to a few arcminutes. Small-scale anisotropy measurements will be contaminated by emission from point sources, so interferometers are needed to identify those sources and remove them. Thus, the entire range of angular scales where CMBR anisotropy is expected will be examined with high sensitivity in the next decade.
This work was supported in part by the National Science Foundation and the National Aeronautical and Space Administration.
27. Scott, P.F., Saunders, R., Pooley. G., O’Sullivan, C., Lasenby. A.N., Jones, M., Hobson, M.P., Duffett-Smith, P.J. & Baker, J. (1996) Astrophys. J.461, L1–L4.
28. Page, L.A. (1997) in Proceedings of the Third International School of Particle Astrophysics, Generation of Large Scale Cosmological Structure. Erice. Sicily, Nov. 3–13, 1996. NATO AFI Series, eds. Schramm. D. & Galeotti, P. (Kluwer, Dordrecht), in press.
33. Crittenden, R.G., Coulson, D. & Turok. N. (1995) Phys. Rev. D52, 5402–5406.
34. Seljak, U. & Zaldarriaga, M. (1997) Phys. Rev. D55,1830–1840.
35. Pospieszalski, M.W., Lakatosh, W.J., Wollack, E., Nguyan, L.D., Le, M., Lui, M. & Liu, T. (1997) in Proceedings of the 1997 IEEE MTT-S International Microwave Symposium, Denver, CO. June 8–13, 1997, IEEE MTT-S Digest, pp. 1285–1288.
36. Hu, W. & White, M. (1996) Astrophys. J.471, 30–51.