Cosmological Parameter Extraction from the First Season of Observations with DASI

TL;DR

This paper constrains cosmological parameters by comparing first-season DASI measurements, together with COBE-DMR, to a seven-parameter adiabatic CDM grid created with CMBFAST. It uses band-power window functions and a Gaussianized chi-square likelihood, incorporating calibration uncertainties and cross-dataset combination with DMR. The results favor a nearly flat, inflationary universe with a scalar spectral index close to unity; the inferred baryon density and non-baryonic CDM densities are compatible with BBN and external data. Under a strong Hubble prior, the data imply Omega_m approx 0.4 and Omega_Lambda approx 0.6, aligning with other cosmological probes. Overall, the work demonstrates that CMB data from DASI and COBE-DMR can yield robust cosmological parameter constraints within inflationary cosmology.

Abstract

The Degree Angular Scale Interferometer (\dasi) has measured the power spectrum of the Cosmic Microwave Background anisotropy over the range of spherical harmonic multipoles 100<l<900. We compare this data, in combination with the COBE-DMR results, to a seven dimensional grid of adiabatic CDM models. Adopting the priors h>0.45 and 0.0<=tau_c<=0.4, we find that the total density of the Universe Omega_tot=1.04+/-0.06, and the spectral index of the initial scalar fluctuations n_s=1.01+0.08-0.06, in accordance with the predictions of inflationary theory. In addition we find that the physical density of baryons Omega_b.h^2=0.022+0.004-0.003, and the physical density of cold dark matter Omega_cdm.h^2=0.14+/-0.04. This value of Omega_b.h^2 is consistent with that derived from measurements of the primordial abundance ratios of the light elements combined with big bang nucleosynthesis theory. Using the result of the HST Key Project h=0.72+/-0.08 we find that Omega_t=1.00+/-0.04, the matter density Omega_m=0.40+/-0.15, and the vacuum energy density Omega_lambda=0.60+/-0.15. (All 68% confidence limits.)

Figures (4)

• Figure 1: Window functions for the DASI band-powers.
• Figure 2: The DASI first-season angular power spectrum in nine bands (closed circles). The DMR information is shown compressed to the single lowest $l$ point. The solid (red) line is the best fitting model which falls on our grid, while the dashed (green) shows the concordance model $(\Omega_b,\Omega_{cdm},\Omega_\Lambda,\tau_c,n_s,h) = (0.05,0.35,0.60,0,1.00,0.65)$. The error bars plotted here are strictly for illustrative purposes only. The $\chi^2$ calculation is made using the full covariance matrix, and after the transformation described in §\ref{['sec:datacomp']}. Thus "Chi-by-eye" can be misleading.
• Figure 3: Marginal likelihood distributions for each dimension of the model grid. The dotted (blue) and solid (black) lines show the distribution before and after the introduction of a weak prior on the Hubble parameter ($h>0.45$). The dashed (red) lines shows the effect of the stronger prior $h=0.72\pm0.08$. In the $\Omega_bh^2$ panel the BBN constraint is shown as a (green) shaded region. All curves are normalized to a peak height of unity, and are spline interpolations of the actual model grid values shown by the points.
• Figure 4: Marginal likelihood distributions when varying the prior on $\tau_c$. All curves assume the weak prior $h>0.45$. The solid (black) are the same as in Figure \ref{['fig:marcons1']} and assume $0.0\leq \tau_c \leq0.4$, while the dashed (red) set $\tau_c=0.0$.