A Measurement of the Angular Power Spectrum of the CMB from l = 100 to 400

TL;DR

This study measures the CMB angular power spectrum in the range $l \approx 100$ to $l \approx 400$ using the TOCO98 data at 144 GHz, complemented by earlier 30–40 GHz observations. The Mobile Anisotropy Telescope (MAT) with D1 and D2 receivers yields consistent results across channels after Jupiter-based beam calibration, with data reduced via Knox filters to obtain accurate $l$-space coverage. The analysis reveals a pronounced peak near $l \approx 200$ with $\delta T_l \approx 82~\mu$K and a decline for $l > 300$, supporting a CMB-dominated anisotropy and disfavoring a peak at higher $l$. When combined with other experiments (COBE/DMR, SK, QMAP), the results align with a concordance cosmology and provide constraints on cosmological parameters, notably suggesting a moderate matter density parameter $\Omega_m h^2$ and a specific peak amplitude.

Abstract

We report on a measurement of the angular spectrum of the CMB between $l\approx 100$ and $l\approx 400$ made at 144 GHz from Cerro Toco in the Chilean altiplano. When the new data are combined with previous data at 30 and 40 GHz, taken with the same instrument observing the same section of sky, we find: 1) a rise in the angular spectrum to a maximum with $δT_l \approx 85~μ$K at $l\approx 200$ and a fall at $l>300$, thereby localizing the peak near $l\approx 200$; and 2) that the anisotropy at $l\approx 200$ has the spectrum of the CMB.

Figures (2)

• Figure 1: The likelihood of the combined $D$1 and $D$2 analysis (solid line) as a function of $\delta T_l^2$. The null tests: quadrature (signal with chopper sweeping one direction minus that with the chopper sweeping the other direction, dotted line), fast and slow dither (differences of subsequent $0.5\rm\,s$ and $10\rm\,s$ averages, dash and dash-dot lines respectively) and first half minus second half (dot-dot-dot-dash line), are also shown. The vertical lines indicate the maximum, $\pm 1\sigma$, or $95$% confidence upper bound.
• Figure 2: Angular spectrum from COBE/DMR, SK, QMAP, TOCO97, and TOCO98$D$-band. The SK data have been recalibrated according to mas99, leading to an increase of 5%, and reduced according to the foreground contribution in doc97, leading to a reduction of 2% (i.e. a net 3% increase in the mean and 5% increase in the error bars over net97). The revised SK calibration error is 11%. The QMAP data are the same as those reported in doc98 and have an average calibration error of 12%. The correction for foreground emission is $\approx$ 2%, though it has not yet been precisely determined and so is not included. Both SK and QMAP are calibrated with respect to Cas-A. The TOCO97 data, which have a calibration error of 10%, are calibrated with respect to Jupiter. The TOCO98 data are shown with $l$-space bandwidth as the horizontal bars. The cosmological models are computed with CMBFAST (selzal). The dashed line is "standard CDM" ($\Omega_m = 1$, $\Omega_{b} = 0.05$, $h=0.5$) the solid line is a "concordance model" (wang99, turn99) with $\Omega_m=0.33$, $\Omega_{b}=0.041$, $\Omega_\Lambda=0.67$, and $h=0.65$. For COBE/DMR we use max97. The error bars are "$1\sigma$ statistical."