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

Sudeep Das, Blake D. Sherwin, Paula Aguirre, John W. Appel, J. Richard Bond, C. Sofia Carvalho, Mark J. Devlin, Joanna Dunkley, Rolando Dunner, Thomas Essinger-Hileman, Joseph W. Fowler, Amir Hajian, Mark Halpern, Matthew Hasselfield, Adam D. Hincks, Renee Hlozek, Kevin M. Huffenberger, John P. Hughes, Kent D. Irwin, Jeff Klein, Arthur Kosowsky, Robert H. Lupton, Tobias A. Marriage, Danica Marsden, Felipe Menanteau, Kavilan Moodley, Michael D. Niemack, Michael R. Nolta, Lyman A. Page, Lucas Parker, Erik D. Reese, Benjamin L. Schmitt, Neelima Sehgal, Jon Sievers, David N. Spergel, Suzanne T. Staggs, Daniel S. Swetz, Eric R. Switzer, Robert Thornton, Katerina Visnjic, Ed Wollack

TL;DR

This work addresses the detection of gravitational lensing of the CMB via the four-point function in ACT temperature maps to measure the convergence power spectrum. It employs an optimal quadratic estimator with a data-driven Gaussian-bias correction based on randomized-phase maps and Monte Carlo null corrections, validated with extensive simulations. The authors report a 4-$\sigma$ detection with an amplitude $A_L=1.16 \pm 0.29$, consistent with $\Lambda$CDM predictions, indicating the lensing signal tracks matter fluctuations around $z\sim2$ at $k\sim0.02\,\mathrm{Mpc}^{-1}$. This result demonstrates CMB lensing can be measured from temperature data alone and sets the stage for more precise Planck and polarization-based measurements in the near future.

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%.

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

TL;DR

This work addresses the detection of gravitational lensing of the CMB via the four-point function in ACT temperature maps to measure the convergence power spectrum. It employs an optimal quadratic estimator with a data-driven Gaussian-bias correction based on randomized-phase maps and Monte Carlo null corrections, validated with extensive simulations. The authors report a 4- detection with an amplitude , consistent with CDM predictions, indicating the lensing signal tracks matter fluctuations around at . This result demonstrates CMB lensing can be measured from temperature data alone and sets the stage for more precise Planck and polarization-based measurements in the near future.

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%.

Paper Structure

This paper contains 7 sections, 1 equation, 4 figures, 1 table.

Table of Contents

  1. Introduction
  2. Data
  3. Methods
  4. Simulations
  5. Results
  6. Null Tests
  7. Implications and Conclusions

Figures (4)

  • Figure 1: Mean convergence power spectrum (red points) from 480 simulated lensed maps with noise similar to our data. The solid line is the input lensing power spectrum, taken from the best-fit WMAP+ACT cosmological model. Error bars correspond to the scatter of power spectrum values obtained from individual maps.
  • Figure 2: Convergence power spectrum (red points) measured from ACT equatorial sky patches. The solid line is the power spectrum from the best-fit WMAP+ACT cosmological model with amplitude $A_L=1$, which is consistent with the measured points. The error bars are from the Monte Carlo simulation results displayed in Fig. \ref{['fig:simulated_cmb']}. The best-fit lensing power spectrum amplitude to our data is $A_L=1.16\pm0.29$
  • Figure 3: Convergence power spectrum for simulated thermal and kinematic SZ maps and point source maps sehgal/etal:2010a which are a good fit to the ACT data. Note that we only show the non-Gaussian contribution, as the Gaussian part which is of similar negligible size is automatically included in the subtracted bias generated by phase randomization. The solid line is the convergence power spectrum due to lensing in the best-fit WMAP+ACT cosmological model.
  • Figure 4: Upper panel: Mean cross-correlation power spectrum of convergence fields reconstructed from different sky patches. The result is consistent with null, as expected. Lower panel: Mean convergence power spectrum of noise maps constructed from the difference of half-season patches, which is consistent with a null signal. The error bars in either case are determined from Monte Carlo simulations, and those in the lower panel are much smaller as they do not contain cosmic variance.