Evidence of Lensing of the Cosmic Microwave Background by Dark Matter Halos (1411.7999v3)

Abstract: We present evidence of the gravitational lensing of the cosmic microwave background by $10^{13}$ solar mass dark matter halos. Lensing convergence maps from the Atacama Cosmology Telescope Polarimeter (ACTPol) are stacked at the positions of around 12,000 optically-selected CMASS galaxies from the SDSS-III/BOSS survey. The mean lensing signal is consistent with simulated dark matter halo profiles, and is favored over a null signal at 3.2 sigma significance. This result demonstrates the potential of microwave background lensing to probe the dark matter distribution in galaxy group and galaxy cluster halos.

Evidence of Lensing of the Cosmic Microwave Background by Dark Matter Halos

The paper "Evidence of Lensing of the Cosmic Microwave Background by Dark Matter Halos," authored by Mathew Madhavacheril and colleagues, presents a paper asserting the gravitational lensing of the Cosmic Microwave Background (CMB) by substantial dark matter halos, with masses around $10^{13}$ solar masses. The work utilizes lensing convergence maps obtained from the Atacama Cosmology Telescope Polarimeter (ACTPol). This paper focuses particularly on examining the lensing effects at the locations of approximately 12,000 CMASS galaxies selected from the SDSS-III/BOSS survey. The observations reveal a statistically significant lensing signal, aligned with predicted patterns from simulated dark matter halo profiles, bearing significance over a null hypothesis at 3.2 standard deviations.

Analytical Techniques and Observational Data

The research leveraged high-resolution CMB data captured by ACTPol, a facility with a 6-meter primary mirror, operating at 146 GHz. Data sampling occurred across several deep field patches during nights, crucial for minimizing atmospheric noise interference. The authors meticulously subtract point sources and calibrate these observations against known Planck maps to ensure accuracy.

The CMASS galaxies used to probe the lensing effects are chosen based on a spectroscopically verified photometric catalog. These galaxies are part of a wider investigation seeking to sample cosmological structure at redshifts $z > 0.4$, aiming for a higher density of data points across large-scale structures at approximately $z = 0.54$.

Results and Significance

The paper employs a stacking technique where lensing convergence maps are centered on the CMASS galaxies. The results showcase an azimuthally averaged lensing profile aligning with theoretical projections from an NFW profile, suggesting a mass of $$M_{200\bar{\rho}_0} = 2.3 \times 10^{13}\, h^{-1} M_{\odot}$$. The maximum significance of the lensing detection, observed over regions within 10 arcminutes of the center, reaches 3.8 sigma against the null hypothesis. This significance is spread across multiple observational patches, underscoring the robustness of results not reliant on isolated regions.

Systematic Checks and Methodology Validation

The authors introduce multiple null tests, including curl tests and random position checks, to authenticate their findings. The methodologies to suppress false detections, like point source contamination via Gaussian filter adjustments, and cross-verifying against random-position-based covariance matrices, establish methodological reliability. These rigorous checks ensure that the observed lensing is indeed due to the mass distribution of targeted structures rather than noise artifacts or external effects like the Sunyaev-Zel'dovich effect.

Broader Implications

The findings elucidate how CMB lensing can effectively map mass distributions at cosmological scales, contributing substantially to our understanding of dark matter halo structures. This is pivotal for honing cosmological models and enhancing our comprehension of mass distribution in the universe. The consistency with previous optical weak-lensing results reinforces the validity of CMB-based methods as a complementary tool to traditional galaxy-bound studies, offering an unobscured cosmic view surpassing the limitations inherent to optical observations.

Conclusion

This body of research heralds a noteworthy advance in leveraging the CMB for cosmological insights, emphasizing the latent potential of CMB lensing for dark matter mapping. As technological precision in this field burgeons, further studies could unravel nuanced details regarding galaxy group evolution and dark matter behavior, with profound implications for theoretical cosmology.