The Atacama Cosmology Telescope: Cosmological parameters from three seasons of data (1301.0824v3)

Abstract: We present constraints on cosmological and astrophysical parameters from high-resolution microwave background maps at 148 GHz and 218 GHz made by the Atacama Cosmology Telescope (ACT) in three seasons of observations from 2008 to 2010. A model of primary cosmological and secondary foreground parameters is fit to the map power spectra and lensing deflection power spectrum, including contributions from both the thermal Sunyaev-Zeldovich (tSZ) effect and the kinematic Sunyaev-Zeldovich (kSZ) effect, Poisson and correlated anisotropy from unresolved infrared sources, radio sources, and the correlation between the tSZ effect and infrared sources. The power ell^2 C_ell/2pi of the thermal SZ power spectrum at 148 GHz is measured to be 3.4 +- 1.4 muK^2 at ell=3000, while the corresponding amplitude of the kinematic SZ power spectrum has a 95% confidence level upper limit of 8.6 muK^2. Combining ACT power spectra with the WMAP 7-year temperature and polarization power spectra, we find excellent consistency with the LCDM model. We constrain the number of effective relativistic degrees of freedom in the early universe to be Neff=2.79 +- 0.56, in agreement with the canonical value of Neff=3.046 for three massless neutrinos. We constrain the sum of the neutrino masses to be Sigma m_nu < 0.39 eV at 95% confidence when combining ACT and WMAP 7-year data with BAO and Hubble constant measurements. We constrain the amount of primordial helium to be Yp = 0.225 +- 0.034, and measure no variation in the fine structure constant alpha since recombination, with alpha/alpha0 = 1.004 +/- 0.005. We also find no evidence for any running of the scalar spectral index, dns/dlnk = -0.004 +- 0.012.

• The paper provides robust ΛCDM parameters by analyzing three seasons of ACT microwave background data.
• It employs comprehensive model fitting to disentangle primary cosmological signals from secondary astrophysical foregrounds including SZ effects.
• The study constrains key metrics such as nₛ, thermal SZ power, Nₑff, and neutrino mass limits, deepening our understanding of early universe physics.

An Analysis of Cosmological and Astrophysical Parameters from the Atacama Cosmology Telescope Data

The presented paper involves a detailed analysis of cosmological parameters derived from observations made by the Atacama Cosmology Telescope (ACT) over three observation seasons from 2008 to 2010. Significantly leveraging high-resolution microwave background maps at 148 GHz and 218 GHz, the paper provides rigorous constraints on primary cosmological parameters within the framework of the Lambda Cold Dark Matter (ΛCDM) model, as well as secondary parameters related to astrophysical processes.

Summary of Methodology and Results

The analysis uses a comprehensive model fitting approach on microwave background data to evaluate a combination of primary cosmological parameters and secondary foreground contributions. Key physical effects incorporated include the thermal and kinematic Sunyaev-Zel'dovich (SZ) effects, Poisson and correlated anisotropies from unresolved infrared and radio sources, and correlations between these effects.

The research synthesizes data from the ACT power spectra with WMAP 7-year temperature and polarization power spectra, ensuring consistency with the ΛCDM model. Among the primary findings is the constraint on the scalar spectral index, $n_s = 0.971 \pm 0.009$, indicating strong agreement with cosmological models predicting deviations from a scale-invariant spectrum.

Notable robust measurements include a thermal SZ power spectrum at $\ell = 3000$ measured at $3.4 \pm 1.4 \, \mu\mathrm{K}^2$. This work establishes the amplitude of the kinematic SZ effect with a 95% confidence level upper limit of $8.6 \, \mu\mathrm{K}^2$, providing valuable insights into cluster physics and the kinetic SZ effects.

The analysis also constrains the number of effective relativistic species in the universe to $N_{\text{eff}} = 2.79 \pm 0.56$, maintaining consistency with the standard value of $3.046$. Moreover, the sum of neutrino masses is limited to $\Sigma m_\nu < 0.39$ eV at 95% confidence when combined with data from Baryon Acoustic Oscillations (BAO) and Hubble constant studies, providing critical insights into neutrino physics.

Theoretical Implications and Future Directions

This paper's findings have significant implications for our understanding of the early universe's conditions, notably concerning the radiation content and phases of matter. The constraints on $N_{\text{eff}}$ and limitations on neutrino mass are integral for models addressing the cosmic neutrino density and exploring physics beyond the standard model, such as additional light particles.

In the future, refining the understanding of the secondary parameters through new data from cross-correlations, expanded lensing analyses, and further microwave background measurements could deepen insights into high-redshift astrophysical phenomena. Continued improvements in experimental techniques and multi-wavelength observations will likely fuel advancements in testing the fine-grained predictions of inflationary cosmology and the structure of dark matter via SZ effects and related signals.

Overall, the presented research exemplifies the power of combining observations from distinct cosmic microwave background (CMB) measurement efforts to nuance the understanding of cosmological models and further fortify the pillars of modern cosmology through empirical evidence.