Cosmological constraints from Archeops

TL;DR

This work uses Archeops CMB data to constrain adiabatic CDM cosmological models by precisely mapping the first acoustic peak and integrating with other CMB and non-CMB priors. It constructs a large model grid and an analytical band-power likelihood to extract parameter constraints, demonstrating consistent measurements of the first peak and supportive results for a flat universe. Combined datasets progressively tighten estimates of $\Omega_{\rm tot}$, $n_s$, and $\Omega_{\rm b}h^2$, while non-CMB priors yield near-final constraints such as $\Omega_{\rm tot} \approx 1$ and $\Omega_\Lambda \approx 0.73$, aligning with inflationary predictions and other cosmological probes.

Abstract

We analyze the cosmological constraints that Archeops places on adiabatic cold dark matter models with passive power-law initial fluctuations. Because its angular power spectrum has small bins in l and large l coverage down to COBE scales, Archeops provides a precise determination of the first acoustic peak in terms of position at multipole l_peak=220 +- 6, height and width. An analysis of Archeops data in combination with other CMB datasets constrains the baryon content of the Universe, Omega(b)h^2 = 0.022 (+0.003,-0.004), compatible with Big-Bang nucleosynthesis and with a similar accuracy. Using cosmological priors obtainedfrom recent non-CMB data leads to yet tighter constraints on the total density, e.g. Omega(tot)=1.00 (+0.03,-0.02) using the HST determination of the Hubble constant. An excellent absolute calibration consistency is found between Archeops and other CMB experiments, as well as with the previously quoted best fit model.The spectral index n is measured to be 1.04 (+0.10,-0.12) when the optical depth to reionization, tau, is allowed to vary as a free parameter, and 0.96 (+0.03,-0.04) when tau is fixed to zero, both in good agreement with inflation.

Figures (7)

• Figure 1: Measurements of the CMB angular power spectrum by Archeops (in red dots) compared with CBDMVC datasets. A $\Lambda$CDM model (see text for parameters) is overplotted and appears to be in good agreement with all the data.
• Figure 2: Gaussian fitting of the first acoustic peak using Archeops and other CMB experiments ($\ell\le 390$). Top panel: 68% CL likelihood contours in the first peak position and FWHM ($\ell_{\rm peak}, FWHM$) plane; Bottom panel: 68% CL likelihood contours in the first peak position and height ($\ell_{\rm peak}, \delta T_{\rm peak}$) plane for different CMB experiments and combinations. The width of the peak is constrained differently by Archeops and BDM experiments, so that the intersection lies on relatively large $\ell_{\rm peak}$. Hence, the BDM + Archeops zone is skewed to the right in the bottom panel.
• Figure 3: Likelihood contours in the $(\Omega_{\Lambda}, \Omega_{\rm tot})$ (left) and $(H_0, \Omega_{\rm tot})$ (right) planes using the Archeops dataset; the three colored regions (three contour lines) correspond to resp. 68, 95 and 99% confidence levels for 2-parameters (1-parameter) estimates. Black solid line is given by the combination Archeops + HST, see text.
• Figure 4: Likelihood contours for (COBE + Archeops + CBI) in the $(\Omega_{\Lambda}, \Omega_{\rm tot})$, $(H_0, \Omega_{\rm tot})$, $(\Omega_{\rm tot}, n)$ and ($\Omega_{\rm b}h^2,n$) planes.
• Figure 5: Likelihood contours in the $(\tau, n)$ and $(\tau, \Omega_{\rm b}h^2)$ planes using Archeops + CBDMVC datasets.