A Measurement of Anisotropy in the Cosmic Microwave Background on 7-22 Arcminute Scales

TL;DR

This paper measures anisotropy in the cosmic microwave background on small scales, identifying foreground contamination and providing constraints on the CMB power spectrum that support flat cosmological models.

Contribution

It presents the first detailed measurement of CMB anisotropy on 7-22 arcminute scales, including foreground removal and spectral analysis, advancing understanding of small-scale CMB fluctuations.

Findings

Detected significant CMB anisotropy with an rms of 82 microKelvin at 31.7 GHz.

Foreground emission correlates with dust emission and is constrained to certain spectral indices.

CMB power spectrum decreases between multipoles 600 and 2000, consistent with flat universe models.

Abstract

We report a measurement of anisotropy in the cosmic microwave background radiation (CMBR) on 7-22 arcminute scales. Observations of 36 fields near the North Celestial Pole (NCP) were made at 31.7 and 14.5 GHz, using the 5.5-meter and 40-meter telescopes at the Owens Valley Radio Observatory (OVRO) from 1993 to 1996. Multi-epoch VLA observations at 8.5 and 15 GHz allow removal of discrete source contamination. After point-source subtraction, we detect significant structure, which we identify with emission from a combination of a steep-spectrum foreground and the CMBR. The foreground component is found to correlate with IRAS 100 micron dust emission. Lack of H-alpha emission near the NCP suggests that this foreground is either high-temperature thermal bremsstrahlung (T_e ~ 10^6 K), flat-spectrum synchrotron or an exotic component of dust emission. On the basis of low-frequency maps of the NCP, we can restrict the spectral index of the foreground to beta >= -2.2. Although the foreground signal dominates at 14.5 GHz, the extracted CMBR component contributes 88\% of the variance at 31.7 GHz, yielding an rms fluctuation amplitude of 82^{+12.1}_{-9.1} microKelvin, including 4.3% calibration uncertainty and 12% sample variance (68% confidence). The equivalent broadband amplitude is dT_{l_e} = 59^{+8.6}_{-6.5} microKelvin at l_e = 589. This measurement, when combined with small angular-scale upper limits obtained at the OVRO, indicates that the CMBR angular power spectrum decreases between l ~ 600 and l ~ 2000 and is consistent with flat cosmological models.