A Measurement of the Cosmic Microwave Background Damping Tail from the 2500-square-degree SPT-SZ survey

Abstract

We present a measurement of the cosmic microwave background (CMB) temperature power spectrum using data from the recently completed South Pole Telescope Sunyaev-Zel'dovich (SPT-SZ) survey. This measurement is made from observations of 2540 deg$^2$ of sky with arcminute resolution at $150\,$GHz, and improves upon previous measurements using the SPT by tripling the sky area. We report CMB temperature anisotropy power over the multipole range $650<\ell<3000$. We fit the SPT bandpowers, combined with the seven-year Wilkinson Microwave Anisotropy Probe (WMAP7) data, with a six-parameter LCDM cosmological model and find that the two datasets are consistent and well fit by the model. Adding SPT measurements significantly improves LCDM parameter constraints; in particular, the constraint on $θ_s$ tightens by a factor of 2.7. The impact of gravitational lensing is detected at $8.1\, σ$, the most significant detection to date. This sensitivity of the SPT+WMAP7 data to lensing by large-scale structure at low redshifts allows us to constrain the mean curvature of the observable universe with CMB data alone to be $Ω_k=-0.003^{+0.014}_{-0.018}$. Using the SPT+WMAP7 data, we measure the spectral index of scalar fluctuations to be $n_s=0.9623 \pm 0.0097$ in the LCDM model, a $3.9\,σ$ preference for a scale-dependent spectrum with $n_s<1$. The SPT measurement of the CMB damping tail helps break the degeneracy that exists between the tensor-to-scalar ratio $r$ and $n_s$ in large-scale CMB measurements, leading to an upper limit of $r<0.18$ (95%,C.L.) in the LCDM+$r$ model. Adding low-redshift measurements of the Hubble constant ($H_0$) and the baryon acoustic oscillation (BAO) feature to the SPT+WMAP7 data leads to further improvements. The combination of SPT+WMAP7+$H_0$+BAO constrains $n_s=0.9538 \pm 0.0081$ in the LCDM model, a $5.7\,σ$ detection of $n_s < 1$, ... [abridged]

Figures (11)

• Figure 1: The 2500 deg$^2$ SPT-SZ survey. We show the full survey region with lightly filtered 95 GHz data from the SPT, using the data and filters which best capture the degree-scale anisotropy of the CMB visible in this figure. The power spectrum measurement reported in this paper is calculated from 2540 deg$^2$ of sky and analyzes 150 GHz data with a different high-pass filter, as described in § \ref{['sec:mapmaking']}.
• Figure 2: The SPT was used to observe 2500 deg$^2$ over 19 individual fields, which are overlaid here on an orthographic projection of the IRAS $100 \, \mu$m dust map from schlegel98. These observation fields were chosen to lie in regions of low dust emission (dark red).
• Figure 3: Left panel: The SPT power spectrum. The leftmost peak at $\ell \sim800$ is the third acoustic peak. Right panel: A comparison of the new SPT bandpowers with other recent measurements of the CMB damping tail from ACBAR reichardt09a, ACT das11, and SPT (K11). Note that the point source masking threshold differs between these experiments which can affect the power at the highest multipoles. In order to highlight the acoustic peak structure of the damping tail, we plot the bandpowers in the right panel as $\ell^4C_{\ell}/(2\pi)$, as opposed to $D_{\ell}=\ell(\ell+1)C_{\ell}/(2\pi)$ in the left panel. The solid line shows the theory spectrum for the $\Lambda$CDM model + foregrounds that provides the best fit to the SPT+WMAP7 data. The bandpower errors shown in these plots contain sample and noise variance terms only; they do not include beam or calibration uncertainties.
• Figure 4: The SPT bandpowers (blue), WMAP7 bandpowers (orange), and the lensed $\Lambda$CDM+foregrounds theory spectrum that provides the best fit to the SPT+WMAP7 data shown for the CMB-only component (dashed line), and the CMB+foregrounds spectrum (solid line). As in Figure \ref{['fig:dl_all']}, the bandpower errors shown in this plot do not include beam or calibration uncertainties.
• Figure 5: The one-dimensional marginalized likelihoods of the six parameters of the $\Lambda$CDM model, plus two derived parameters: the dark energy density $\Omega_{\Lambda}$ and the Hubble constant $H_0$. The constraints are shown for the SPT-only (blue dot-dashed lines), WMAP7-only (red dashed lines), and SPT+WMAP7 (black solid lines) datasets. With the exception of $\tau$, the SPT bandpowers constrain the parameters approximately as well as WMAP7 alone. In particular, the SPT bandpowers measure the angular sound horizon $\theta_s$ extremely well because they measure seven acoustic peaks. In the SPT-only constraints, the WMAP7 measurement of $\tau$ has been applied as a prior; because of this we do not plot an SPT-only line on the $\tau$ plot.