Detection of the Power Spectrum of Cosmic Microwave Background Lensing by the Atacama Cosmology Telescope (1103.2124v3)

Abstract: We report the first detection of the gravitational lensing of the cosmic microwave background through a measurement of the four-point correlation function in the temperature maps made by the Atacama Cosmology Telescope. We verify our detection by calculating the levels of potential contaminants and performing a number of null tests. The resulting convergence power spectrum at 2-degree angular scales measures the amplitude of matter density fluctuations on comoving length scales of around 100 Mpc at redshifts around 0.5 to 3. The measured amplitude of the signal agrees with Lambda Cold Dark Matter cosmology predictions. Since the amplitude of the convergence power spectrum scales as the square of the amplitude of the density fluctuations, the 4-sigma detection of the lensing signal measures the amplitude of density fluctuations to 12%.

• The paper presents the first detection of the CMB lensing power spectrum with a 4σ significance using a four-point correlation function analysis.
• It employs ACT data over a 324-square-degree sky segment with superconducting bolometers and rigorous noise filtering to isolate the lensing signal.
• Simulations and null tests validate the measured amplitude (A_L = 1.16 ± 0.29), aligning the results with ΛCDM predictions and advancing dark matter studies.

Detection of the Power Spectrum of Cosmic Microwave Background Lensing by the Atacama Cosmology Telescope

The paper, "Detection of the Power Spectrum of Cosmic Microwave Background Lensing by the Atacama Cosmology Telescope", presents a significant analysis within the field of cosmology by detailing the observation of gravitational lensing effects on the Cosmic Microwave Background (CMB). Utilizing data from the Atacama Cosmology Telescope (ACT), the authors report the first detection of the gravitational lensing of the CMB via a four-point correlation function analysis in temperature maps. This research notably aligns the measured convergence power spectrum with theoretical predictions, offering substantial verification of Lambda Cold Dark Matter (ΛCDM) cosmology.

Methodology Overview

The ACT operates with arrays of superconducting transition-edge sensing bolometers and focuses on multiple frequency bands. The research examined temperature maps over a substantial 324-square-degree segment of the sky with measurements performed over three observing seasons at 148 GHz. The analytical focus is on the angular scales of 2 degrees, rendering precise measurements of the gravitational lensing signal robust through the optimal quadratic estimator method. A comprehensive approach was undertaken to filter and process the temperature maps, specifically targeting the removal of atmospheric noise, scan-synchronous artifacts, and the contamination from astrophysical sources.

Simulations and Verification

The robustness of the results was validated through rigorous simulations. Multiple lensed and unlensed maps were formulated using Gaussian random fields based on the WMAP+ACT temperature power spectrum. These simulations allowed the researchers to assess the accuracy and consistency of lensing reconstruction techniques, demonstrating their capacity to retrieve the lensing spectrum from the data while managing substantial noise contributions effectively.

Results

The research found the amplitude of the measured lensing convergence power spectrum to be $A_L = 1.16 \pm 0.29$, consistent with theoretical models predicted by the ΛCDM framework, indicating a 4σ detection significance. The analysis inferred a direct measurement of the amplitude of matter fluctuations at comoving length scales around 100 Mpc, at redshifts between 0.5 and 3, reflecting a high agreement with expected cosmological parameters.

Contamination and Error Management

Throughout the research, an emphasis was placed on mitigating various sources of contamination. Extensive tests using simulated data maps with known foreground signals (e.g., thermal and kinetic SZ signals, and point source interference) demonstrated a significant reduction in their impact on the results. The authors utilized rigorous null tests and cross-validation checks to affirm the purity of the lensing signal. These procedures were crucial for validating the claim that the observed lensing signal was untainted by extraneous astrophysical interferences.

Implications and Future Directions

This detection elucidates the lensing of the CMB as an effective cosmic probe for studying dark matter distribution and supporting the established ΛCDM cosmological model. The research sets the stage for future investigations into the universe's large-scale structure with enhanced precision. The results underline the potential insights that could be derived from upcoming data from instruments like the Planck satellite and advanced polarization detectors including ACTPol and SPTPol. Additionally, future mission proposals are motivated to exploit CMB polarization for refinements in lensing measurements, aiming for profound cosmological insights.

This paper posits a foundational step towards comprehensive CMB lensing analysis, stimulating further exploration into gravitational lensing's cosmological impacts and bolstering the understanding of underlying physics in the universe's composition and evolution.