Observational cosmology

We participate in two cosmology satellite missions of the European Space Agency, Planck and Euclid. The Planck satellite ceased operations in October 2013, but analysis of its data will continue until end of 2015. The planned launch date for Euclid is in March 2020.

By end of 2014, the Planck Collaboration had almost completed the analysis for the second major data release, and preliminary cosmological results were already presented in conferences in Ferrara (http://www.cieffeerre.it/Eventi/eventi-in-programmazione-nel-2014/planck-2014-the-microwave-sky-in-temperature-and-polarization/PLANCK-2014 ) and Paris ( http://www.iap.fr/col2014/ ) in December 2014.

Planck observed the microwave sky in nine frequencies. The main purpose of the mission was to measure the temperature anisotropies and the polarization of the cosmic microwave background (CMB) over the whole sky with unprecedented accuracy.  In the first data release, only CMB temperature data was used, and the focus in the analysis for the second release has been on the CMB polarization.

We have been responsible for producing the sky maps (Fig.10 and 11) for the three frequencies (30, 44 and 70 GHz) of Planck’s Low Frequency Instrument (LFI), as well as for a number of related tasks, including null tests on the maps, estimation of their residual noise correlations, and producing large Monte Carlo simulations of the data. We have also contributed to development of improved calibration methods for LFI and fitted cosmological models of primordial isocurvature perturbations to Planck data.

Microwave sky

Figure 10. The polarization of the microwave sky at the two lowest frequencies, 30 and 44 GHz, measured by Planck. Polarization is represented by the two Stokes parameters Q and U, Q giving the vertical (Q positive) or horizontal (Q negative) polarization component, U the diagonal component. These maps are in Galactic coordinates. At 30 GHz the polarization is dominated by synchrotron radiation from our own Galaxy. (ESA/Planck Collaboration, preliminary)

Microwave sky

Figure 11. The polarization of the microwave sky at the Planck 70GHz and 353 GHz channels. At 353 GHz the polarization is dominated by radiation from dust in our own galaxy, but at 70 GHz the cosmic microwave background dominates except near the Milky Way (the horizontal band in the middle). (ESA/Planck Collaboration, preliminary)

By combining the measurements at different frequencies the cosmic microwave background can be separated from other microwave radiation. The CMB is then analysed in terms of its angular power spectra (Fig. 12), which are compared to predictions from cosmological models to select between models and to determine the values of their parameters. The new results remain in agreement with the 5-parameter standard cosmological model, the LambdaCDM model, where the main energy/matter components of the universe are dark energy, cold dark matter (CDM), and ordinary matter, with a uniform time-independent density of dark energy (the cosmological constant "Lambda"), and the primordial perturbations responsible for the origin of structure were statistically simple ("Gaussian") and almost, but not quite, scale independent, as predicted by the simplest cosmological "inflation" models.

The next cosmology mission after Planck will be Euclid. Euclid will address some of the main open questions in cosmology, in particular the mystery of dark energy: what is causing the accelerated expansion of the universe? Euclid will observe the last three quarters - about 10 billion years - of the history of the universe; complementing Planck, whose cosmological measurements are mainly from the 400 000 year old early universe. We participate in the development of data analysis methods for Euclid and will eventually analyze a part of the Euclid data. We operate one of the nine Euclid Science Data Centers, SDC-Finland. To provide a uniform environment for the Euclid analysis codes, the SDCs operate on virtual machines. Currently the virtual machines of SDC-Finland run on the Pouta cloud service at the CSC Kajaani Data Center, and we have participated in and passed the four first "SDC challenges" devised by the Euclid system team. In the latest challenge, the SDCs produced simulated Euclid data in a coordinated manner, so that requests for simulated data and the produced data were passed through a central Euclid Archive System connected to all SDCs.


Figure 12. Angular power spectra of the polarization of the cosmic microwave background, showing how strong the polarization structure is at each angular scale on the sky. The polarization pattern on the sky can be divided into an E mode (divergence) and a B mode (curl). The CMB polarization is mainly in the E mode. The right panel shows the strength of CMB E-mode polarization and the left panel its correlation with the CMB temperature anisotropy. The horizontal axis gives the angular scale in terms of the multipole number l; the corresponding angle is roughly 180 degrees / l. The blue dots are measurements by Planck; the red curve is the prediction of the standard LambdaCDM cosmological model with parameter values fit to the CMB temperature data. The bottom of each panel gives the residuals, i.e. difference of data from model, in an expanded scale. (ESA/Planck Collaboration, preliminary)