The Atacama Cosmology Telescope: DR4 Maps and Cosmological Parameters (2007.07288v2)

Abstract: We present new arcminute-resolution maps of the Cosmic Microwave Background temperature and polarization anisotropy from the Atacama Cosmology Telescope, using data taken from 2013-2016 at 98 and 150 GHz. The maps cover more than 17,000 deg$^2$, the deepest 600 deg$^2$ with noise levels below 10 $\mu$K-arcmin. We use the power spectrum derived from almost 6,000 deg$^2$ of these maps to constrain cosmology. The ACT data enable a measurement of the angular scale of features in both the divergence-like polarization and the temperature anisotropy, tracing both the velocity and density at last-scattering. From these one can derive the distance to the last-scattering surface and thus infer the local expansion rate, $H_0$. By combining ACT data with large-scale information from WMAP we measure $H_0 = 67.6 \pm 1.1$ km/s/Mpc, at 68% confidence, in excellent agreement with the independently-measured Planck satellite estimate (from ACT alone we find $H_0 = 67.9 \pm 1.5$ km/s/Mpc). The $\Lambda$CDM model provides a good fit to the ACT data, and we find no evidence for deviations: both the spatial curvature, and the departure from the standard lensing signal in the spectrum, are zero to within 1$\sigma$; the number of relativistic species, the primordial Helium fraction, and the running of the spectral index are consistent with $\Lambda$CDM predictions to within $1.5 - 2.2\sigma$. We compare ACT, WMAP, and Planck at the parameter level and find good consistency; we investigate how the constraints on the correlated spectral index and baryon density parameters readjust when adding CMB large-scale information that ACT does not measure. The DR4 products presented here will be publicly released on the NASA Legacy Archive for Microwave Background Data Analysis.

• The paper provides enhanced CMB maps detailing temperature and polarization anisotropies over 17,000 square degrees.
• The paper accurately measures key parameters such as the Hubble constant, reporting an independent value of 67.6±1.1 km/s/Mpc.
• The paper confirms the consistency of the ΛCDM model and extends multipole analysis to improve understanding of damping tail physics.

Overview of "The Atacama Cosmology Telescope: DR4 Maps and Cosmological Parameters"

The paper entitled "The Atacama Cosmology Telescope: DR4 Maps and Cosmological Parameters" presents the results from the fourth data release (DR4) of the Atacama Cosmology Telescope (ACT), encompassing significant observations conducted from 2013 to 2016. The research provides new insights into the Cosmic Microwave Background (CMB) radiation through high-resolution maps that considerably expand the existing datasets with observations over approximately 17,000 square degrees, including deep fields with noise levels below 10 µK-arcmin over 600 square degrees.

Key Achievements

1. Enhanced CMB Mapping: The ACT DR4 data deliver high-resolution temperature and polarization maps of the CMB, pushing the boundaries of cosmological research by offering new temperature measurements that reveal the angular scale of the features related to the velocity and density of the universe's structure at the last-scattering surface.
2. Cosmological Parameters: From these detailed maps, the paper constrains several fundamental cosmological parameters. Notably, the Hubble constant, $H_0$, is independently measured as $67.6\pm 1.1$ km/s/Mpc. This value aligns well with past measurements, particularly the $H_0$ derived from the Planck satellite data.
3. Consistency with $\Lambda$CDM Model: The analysis confirms that the $\Lambda$CDM model still provides an excellent fit for these new data. No significant deviations or new physics seem to be required within the assessed scope. Parameters like spatial curvature, number of relativistic species, and the primordial helium fraction maintain consistency with the $\Lambda$CDM predictions.
4. Extended Multipole Range: The ACT DR4 dataset significantly contributes with new high-resolution data to enhance the examination of the damping tail physics at $\ell > 1500$, as well as secondary anisotropies. This provides an invaluable resource for cosmological models focusing on late-time effects such as gravitational lensing and Integrated Sachs-Wolfe effects.

Implications

The ACT DR4 results carry significant implications for the field of cosmology. The impressive agreement with the $\Lambda$CDM model consolidates its position as the standard cosmological model. The consistency in the Hubble constant measurement further reinforces the reliability of CMB-derived cosmological parameters, even amidst ongoing discourse about $H_0$ discrepancies with local measurements, like those using Cepheid variables.

Future Directions

With the DR4 dataset extending the sky coverage and improving the precision of cosmological measurements, future research can focus on employing these maps to further scrutinize small-scale anisotropies and refine cosmological models. Furthermore, upcoming releases, expected to cover even greater sky areas with increased detector sensitivity, will undoubtedly sharpen constraints on the fundamental parameters of the universe, test new physics, and possibly reconcile the $H_0$ tension.

In conclusion, the paper delivers substantial progress in observational cosmology, reflecting advancements in both measurement techniques and theoretical interpretation, with the ACT DR4 data setting the stage for more comprehensive and precise cosmic investigations.