The Atacama Cosmology Telescope: A CMB lensing mass map over 2100 square degrees of sky and its cross-correlation with BOSS-CMASS galaxies

Abstract: We construct cosmic microwave background lensing mass maps using data from the 2014 and 2015 seasons of observations with the Atacama Cosmology Telescope (ACT). These maps cover 2100 square degrees of sky and overlap with a wide variety of optical surveys. The maps are signal dominated on large scales and have fidelity such that their correlation with the cosmic infrared background is clearly visible by eye. We also create lensing maps with thermal Sunyaev-Zel'dovich contamination removed using a novel cleaning procedure that only slightly degrades the lensing signal-to-noise ratio. The cross-spectrum between the cleaned lensing map and the BOSS CMASS galaxy sample is detected at $10$-$\sigma$ significance, with an amplitude of $A=1.02 \pm 0.10$ relative to the Planck best-fit LCDM cosmological model with fiducial linear galaxy bias. Our measurement lays the foundation for lensing cross-correlation science with current ACT data and beyond.

Overview of ACT CMB Lensing × BOSS

The research paper presents a detailed study of cosmic microwave background (CMB) lensing mass maps using observations from the Atacama Cosmology Telescope (ACT) for the 2014 and 2015 seasons, covering an extensive area of 2100 square degrees. This research is distinguished by its methodology, robust dataset, and its significant contribution to cosmological analyses, particularly in cross-correlation studies with the BOSS-CMASS galaxy sample.

Methodology and Data

The authors have employed sophisticated techniques to construct CMB lensing mass maps that are crucial for investigating the large-scale structure of the universe. ACT data, characterized by high-resolution measurements in the 98 GHz and 150 GHz frequency bands, served as the primary dataset. Several preprocessing steps were meticulously applied, including source subtraction and inpainting, to enhance data quality. A noteworthy methodological advancement in this paper is the novel approach for thermal Sunyaev-Zel'dovich (tSZ) contamination removal. This method, while slightly reducing the signal-to-noise ratio of the lensing maps, effectively cleanses the dataset of significant foreground contaminants.

Results and Significance

The cross-correlation of the cleaned CMB lensing maps with BOSS CMASS galaxies was detected at an impressive 10-sigma significance level. The amplitude of this detection aligns well with predictions from the Planck best-fit ΛCDM cosmological model, with a measured amplitude of $A = 1.02 \pm 0.10$. This level of precision underscores the viability of these maps for future cosmological studies, especially those leveraging cross-correlation techniques to explore the mass distribution and the influence of dark energy and other cosmological parameters.

Implications

The implications of this research are far-reaching. Firstly, the construction and cleaning of lensing maps forge a path for more precise cosmological models by mitigating biases induced by tSZ effects. Secondly, these maps provide an invaluable resource for studying the cross-correlation with various large-scale structure tracers, thereby aiding in the breakdown of potential degeneracies in galaxy bias and the amplitude of matter density fluctuations ($\sigma_8(z)$). Such reconciliations are pivotal in probing extensions to the standard cosmological model, including modified gravity theories and neutrino masses.

Future Developments and Challenges

The release of these CMB lensing maps sets the stage for more extensive cross-correlation analyses as larger, more sensitive CMB datasets become available. The methodological framework presented also opens the door for the application of tSZ-cleaned techniques in future surveys, potentially extending the redshift reach and thereby enhancing the cosmological utility of CMB lensing. Nonetheless, challenges remain, particularly in the form of residuals from other extragalactic foregrounds like the cosmic infrared background (CIB) and kinetic Sunyaev-Zel'dovich (kSZ) effect, which need further methodological innovation to adequately address.

This work constitutes a robust foundation for upcoming ACT and other CMB experiments. By refining the techniques of cross-correlation and tSZ contamination removal, this research enhances the precision and reliability of cosmological inference, offering promising avenues for future exploration and discovery in the field.