Analysis of Small and Medium-Scale Cosmic Microwave Background Experiments

Abstract

Anisotropies in the temperature of the cosmic microwave background have been detected on a range of scales by several different experiments. These anisotropies reflect the primordial spectrum of metric perturbations in the early universe. In principle, the largest barrier to a clean interpretation of the experimental results is contamination by foreground sources. We address this issue by projecting out likely sources of foreground contamination {}from seven separate small-angle and medium-angle experiments. We then calculate likelihood functions for models with adiabatic perturbations, first for the amplitude of the spectrum while constraining the spectral index to be $n=1$, and then jointly for the amplitude and spectrum of the fluctuations. All of the experiments are so far consistent with the simplest inflationary models; for $n=1$ the experiments' combined best-fit quadrupole amplitude is $Q_{\rm rms-ps}= 18^{+3}_{-1} \,\,μK$, in excellent agreement with the COBE two-year data. In ($Q_{\rm rms-ps}$, n) space, the allowed region incorporating intermediate and small-scale experiments is substantially more constrained than {}from COBE alone. We briefly discuss the expected improvement in the data in the near future and corresponding constraints on cosmological models.