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 at least until 2016. The planned launch date for Euclid is in December 2020.

In 2015, the Planck collaboration completed the analysis for the second data release, which is now available at the Planck Legacy Archive, and which resulted in the 28 “Planck 2015 results” publications ( http://www.cosmos.esa.int/web/planck/ ). 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 the first 15 months of data and only the CMB temperature data was used, whereas the second data release included all 4 years of data and both temperature and 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.

The new results remain in agreement with the 5-parameter standard cosmological model, the LambdaCDM model:  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 values of these parameters were determined with greater accuracy: Dark energy makes up 69.2%±1.2%, cold dark matter 26.0%±1.2% and ordinary matter 4.8%±0.2%  of the total energy.  The universe expands at a rate of 67.8±0.9 km/s/Mpc (the Hubble constant).  The primordial perturbations deviate from scale invariance by  3.2±0.6% (the spectral index), the negative value indicating that perturbations were slightly stronger at larger distance scales.  

From the fraction of CMB photons that were observed to be scattered by interstellar free electrons, 6.6±1.6%, it was determined that the first stars (whose radiation ionized the interstellar gas to free these electrons) were formed 550 million years after the big bang.  This was a revision upwards from the earlier determination by the NASA WMAP satellite, 450 million years.  The age of the universe was determined to be 13.80±0.04 billion years.

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, located at the Kajaani facility of CSC  - IT Center for Science. To provide a uniform environment for the Euclid analysis codes, the SDCs operate on virtual machines.  


Figure 1. The sky at the nine different microwave frequency bands of Planck, in galactic coordinates.  Microwave emission from our galaxy dominates in the direction of the Milky Way at all frequencies; but at the six lowest frequencies, the cosmic microwave background anisotropy dominates above and below it. (Planck Collaboration: Planck 2015 results. I. Overview of products and scientific results. arXiv:1502.01582v2, submitted to Astronomy & Astrophysics.)


Figure 2. The gravitational effect of mass concentrations in the universe bends the path of the cosmic microwave background photons.  The resulting distortion of the CMB map was observed by Planck and was used to determine the matter distribution in the universe, over the whole sky, projected along line of sight.  (More technically, this is the map of the CMB lensing potential, which give more weight to masses that are closer to half-way along the path of the photon.) In this figure lighter color corresponds to more matter (which is mostly cold dark matter).  Dark grey correspond to directions obscured by the Milky Way.  (Planck Collaboration: Planck 2015 results. I. Overview of products and scientific results. arXiv:1502.01582v2, submitted to Astronomy & Astrophysics.)


Figure 3. Sunyaev-Zeldovich effect. Energetic electrons in galaxy clusters scatter CMB photons to higher frequencies, distorting the CMB spectrum in direction of galaxy clusters.  Planck can see this effect and it is used to discover galaxy clusters and study their structure.  This figure is a map of the Compton y-parameter, giving the magnitude of this spectral distortion, as observed by Planck over the whole sky.  The northern galactic hemisphere is shown on the left; the two most prominent galaxy clusters are the Coma cluster near the north galactic pole (at center) and the Virgo cluster to the right of it. The southern glactic hemisphere is on the right.  (Planck Collaboration: Planck 2015 results. I. Overview of products and scientific results. arXiv:1502.01582v2, submitted to Astronomy & Astrophysics.)


Figure 4. The Planck constraints on the spectral index (horizontal axis) and primordial gravitational waves (vertical axis) compared to predictions if a several popular cosmological inflation models.  The structure in our universe is thought to originate from quantum fluctuations during cosmological inflation in the early universe, but there are many different possible models of inflation.  Planck results rule out many such models, but many other models fit these results. The region allowed by Planck is shown in blue, dark blue is the 68% confidence region and light blue the 95% confidence region.   (Planck Collaboration: Planck 2015 results. XX. Constraints on inflation. arXiv:1502.02114v1, submitted to Astronomy & Astrophysics.)