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CMB

Summary and figures of the currently available experimental data on CMB temperature anisotropies. A couple of packages for download, including a C version of the WMAP likelihood code.

NEWS

previous news
  • 10.07.03: I am now in Switzerland. News and features on this page.
  • 01.07.03: New 'Talks and posters' page here with abstracts and downloads of slides and posters in PDF format.
  • 01.07.03: I have come back from Wales and I have put the slides of my seminar here. I am on my way to Switzeland to write up and any other plans can be found here.
  • 28.05.03: Less cluttered navigation. Publications now available here. Also, I have added an online research proposal here.
  • 16.05.03: Another update, another design :). I have now written my WMAP page with a C version of the likelihood code for download and some recent results.

Publications

List of publications with abstracts and links.

Talks and posters

List of talks an posters with abstracts and downloads.

Contact: Carolina Ödman

Publications


  • astro-ph/0305254:
    The shape of the CMB power spectrum.
    C. J. Ödman

    Abstract:

    The recent WMAP data represents a milestone in cosmology and helps constrain cosmological parameters with unprecedented accuracy. In this work we combine the WMAP data with previous CMB anisotropy measurements at smaller angular scales to characterize the shape of the CMB anisotropy power spectrum.
    We carry out a phenomenological analysis of the data. By allowing non-physical shapes of the power spectrum we analyse high and low frequency experiments separately and together. We find that WMAP dramatically constrains the power spectrum up to l ~ 700. On smaller scales, the data show discrepancies that can be associated with experimental systematics.
    If we combine all types of experiments, the observable features in the power spectrum are in excellent agreement with the WMAP cosmological parameter estimation.
    This work illustrates the advantages of a model-independent approach to understanding experimental systematics that might affect CMB observations.
    New Astronomy Reviews, Proceedings of the CMBNET Meeting, 20-21 February 2003, Oxford, UK, submitted.

  • astro-ph/0302361:
    Current constraints on Cosmological Parameters from Microwave Background Anisotropies .
    A. Melchiorri, C. J. Ödman

    Abstract:

    We compare the latest observations of Cosmic Microwave Background (CMB) anisotropies with the theoretical predictions of the standard scenario of structure formation. Assuming a primordial power spectrum of adiabatic perturbations we found that the total energy density is constrained to be Ωtot = 1.03 ± 0.06 while the energy density in baryon and Cold Dark Matter (CDM) are Ωbh2 = 0.021 ± 0.003 and Ωcdmh2 = 0.12 ± 0.02, (all at 68% C.L.) respectively. The primordial spectrum is consistent with scale invariance, (nS = 0.97 ± 0.04) and the age of the universe is t0 = 14.6 ± 0.9 Gyrs. Adding informations from Large Scale Structure and Supernovae, we found a strong evidence for a cosmological constant ΩΛ = 0.70-0.05+0.07 and a value of the Hubble parameter h = 0.69 ± 0.07. Restricting this combined analysis to flat universes, we put constraints on possible 'extensions' of the standard scenario. A gravity waves contribution to the quadrupole anisotropy is limited to be r <= 0.42 (95% c.l.). A constant equation of state for the dark energy component is bound to be wQ <= -0.74 (95% c.l.). We constrain the effective relativistic degrees of freedom Nν <= 6.2 and the neutrino chemical potential -0.01 <= ξe <= 0.18 and ξμ τ <= 2.3 (massless neutrinos).
    Physical Review D 67, 081302(R) (2003)

  • astro-ph/0212495:
    The CMB power spectrum out to l=1400 measured by the VSA.
    K. Grainge et al. for the VSA collaboration

    Abstract:

    We have observed the cosmic microwave background (CMB) in three regions of sky using the Very Small Array (VSA) in an extended configuration with antennas of beamwidth 2 degrees at 34 GHz. Combined with data from previous VSA observations using a more compact array with larger beamwidth, we measure the power spectrum of the primordial CMB anisotropies between angular multipoles l = 160 - 1400. Such measurements at high l are vital for breaking degeneracies in parameter estimation from the CMB power spectrum and other cosmological data. The power spectrum clearly resolves the first three acoustic peaks, shows the expected fall off in power at high l and starts to constrain the position and height of a fourth peak.
    MNRAS, 341, 4, L23

  • astro-ph/0211522:
    The State of the Dark Energy Equation of State.
    A. Melchiorri, L. Mersini, C. J. Ödman, M. Trodden

    Abstract:

    By combining data from seven cosmic microwave background experiments with large scale structure data, the Hubble parameter measurement from the Hubble Space Telescope and luminosity measurements of Type Ia supernovae we demonstrate the bounds on the dark energy equation of state parameter wQ to be -1.62 < wQ < -0.74 at the 95% confidence level. Although our limit on wQ is improved with respect to previous analyses, cosmological data does not rule out the possibility that wQ is less than -1. We present a tracking model that ensures wQ <= -1 at recent times and discuss the observational consequences.
    PRD, submitted

  • astro-ph/0210606:
    The Inflationary Gravity Waves in light of recent Cosmic Microwave Background Anisotropies data.
    A. Melchiorri, C. J. Ödman

    Abstract:

    One of the major predictions of inflation is the existence of a stochastic background of cosmological gravitational waves (GW). These gravitational waves can induce significant temperature anisotropies in the Cosmic Microwave Background (CMB) on the angular scales recently probed by the Archeops experiment. Here, we perform a combined analysis of Archeops together with information from other CMB experiments and/or cosmological datasets, in order to constrain the amplitude of the GW background. We find that, for a scale-invariant GW background, the ratio of tensor/scalar perturbations at the CMB quadrupole is now constrained to be r <= 0.43 at 95% c.l., while thebound on the spectral index of primordial density fluctuations is nS = 0.97 -0.12+0.10. We discuss the implications for future GW detections through CMB polarization measurements.
    Phys. Rev. D 67, 021501(R) (2003)

  • Proceeding
    Cosmological Parameters from Cosmic Microwave anisotropies: Status and Prospects..
    A. Melchiorri, C. J. Ödman

    Abstract:

    A survey is made of the present constraints on cosmological parameters from cosmic microwave background anisotropies.
    Astrophysics and Space Science 283 (4): 457-468, 2003.

  • astro-ph/0212566
    Dark energy: Is it Q or Λ?.
    A. Melchiorri, C. J. Ödman

    Abstract:

    New observations of cosmic microwave background anisotropies, supernovae luminosity distances and galaxy clustering are sharpening our knowledge about dark energy. Here we present the latest constraints.
    Proceedings of the XVIII IAP Colloquium "On the nature of dark energy" Paris, July 2002.

  • astro-ph/0207286:
    Constraining the shape of the CMB: a Peak-by-peak analysis.
    C. J. Ödman, A. Melchiorri

    Abstract:

    The recent measurements of the power spectrum of Cosmic Microwave Background anisotropies are consistent with the simplest inflationary scenario and big bang nucleosynthesis constraints. However, these results rely on the assumption of a class of models based on primordial adiabatic perturbations, cold dark matter and a cosmological constant. In this paper we investigate the need for deviations from the Λ-CDM scenario by first characterizing the spectrum using a phenomenological function in a 15 dimensional parameter space. Using a Monte Carlo Markov chain approach to Bayesian inference and a low curvature model template we then check for the presence of new physics and/or systematics in the CMB data. We find an almost perfect consistency between the phenomenological fits and the standard Λ-CDM models. The improved spectral resolution expected from future satellite experiments is warranted for a definitive test of the scenario.
    Physical Review D67, 083511 (2003).

  • astro-ph/0205367:
    First results from the Very Small Array -- IV. Cosmological parameter estimation .
    Jose Alberto Rubino-Martin et al. for the VSA collaboration

    Abstract:

    We investigate the constraints on basic cosmological parameters set by the first compact-configuration observations of the Very Small Array (VSA), and other cosmological data sets, in the standard inflationary LambdaCDM model. Using a weak prior 40 < H0 < 90 km/s/Mpc we find that the VSA and COBE data alone produce the constraints Ωtot = 1.03 ± 0.12, Ωbh2 = 0.029 ± 0.009, Ωcdmh2 = 0.13-0.05+0.08 and nS = 1.04-0.08+0.11 at the 68 per cent confidence level. Adding in the type Ia supernovae constraints, we additionally find Ωm = 0.32-0.06+0.09 and ΩΛ = 0.71 ± 0.07. These constraints are consistent with those found by the BOOMERanG, DASI and MAXIMA experiments. We also find that, by combining all these CMB experiments and assuming the HST key project limits for H0 (for which the X-ray plus Sunyaev--Zel'dovich route gives a similar result), we obtain the tight constraints Ωm = 0.28-0.07+0.14 and ΩΛ = 0.72-0.13+0.07, which are consistent with, but independent of, those obtained using the supernovae data.
    MNRAS, 341, 4, 1084