The discovery of the cosmic microwave background (CMB) radiation at 2.7 degrees above the absolute zero marked the start of what may be called physical cosmology. The CMB radiation is the leftover from the Big Bang itself and has cooled in the billions of years since, because of the expansion of the Universe. These days we are busy exploring the data from the experiment Planck, which are challenging the standard cosmological model through observations with extremely high precision.
This (artist's drawing) illustration shows Planck orbiting the second Lagrange point (L2), 1.5 million kilometers from Earth. Illustration: ESA/C. Carreau
About the project
Cosmology is the study of the Universe on large scales, scales larger than individual galaxies. Until about 50 years ago, the main quest was to determine the expansion “velocity” and the average density. Cosmology has after the mid-sixties become a much more varied and lively field of research. Today cosmology is a leading branch of both astronomy and physics.
The discovery of the cosmic microwave background (CMB) radiation at 2.7 degrees above the absolute zero marked the start of what may be called physical cosmology. The CMB radiation is the leftover from the Big Bang itself and has cooled in the billions of years since, because of the expansion of the Universe. The study of this radiation has given us an understanding of what happened in the first minutes of the history of the Universe, when light nuclei like helium were formed.
The last decade has seen an enormous growth in cosmology. While cosmology until one or two decades ago was a data-starved science, the opposite is the case today. The wealth of new data coming out of new large space- and ground-based observatories and experiments has made cosmology a data-rich science where one poses detailed questions and where simplified models are no longer sufficient. Already with NASA’s Wilkinson Microwave Anisotropy Probe (WMAP), large classes of cosmological models were ruled out, and a concordance model was established. These days we are busy exploring the data from the new experiment Planck, which will challenge this model through observations with extremely high precision.
In 1999, guaranteed by the Research Council, the Institute of Theoretical Astrophysics became a full member of the Low-Frequency Instrument consortium in the Planck collaboration. On the instrumental side, the Norwegian contribution was defined to be the Electrical Ground Support Equipment (EGSE) required for testing the fully assembled instrument prior to launch. All these commitments were fulfilled from the Norwegian side in 2004, and the EGSE was successfully used in the integration and testing of the LFI instrument that was operating on Planck from the successful launch in May 2009 until it was turned off on the 19th of October, 2013.
The aim of Planck is to produce a very accurately calibrated mapping of the temperature and polarization of the microwave and far IR radiation all over the sky with an angular resolution of 10’, sensitivity better than 10 microkelvin and with 9 frequency channels spaced between 30 and 900 GHz. While the satellite, launch and satellite operation was the responsibility of ESA, there were two instruments that were provided by science teams:
- The High Frequency Instrument (HFI), which has 6 channels placed at 100, 143, 217, 353, 545 and 857 GHz. Its angular resolution is from 10.7 arc minutes for the lowest frequency to 5.5 for the 4 highest. The 100, 143, 217 and 353 GHz channels measure polarization.
- The Low Frequency Instrument (LFI) has 3 frequency channels, at 30, 44 and 70 GHz. The angular resolution is 33, 23 and 14 arc minutes for each of the channels respectively. All channels measure polarization.
In 1999, Norway was accepted as a full member of the LFI consortium. Per B. Lilje was accepted as Co-Investigator (Co-I) in the LFI project, representing the Norwegian interests in all Planck fora, while several scientists at the Institute of Theoretical Astrophysics have since been accepted as Associates or Collaborators in the project; presently Lilje, Frode Hansen, Hans Kristian Eriksen, postdocs Yashar Akrami, Phil Bull and Yabebal Tadesse and Ph.D. students Eirik Gjerløw, Kristin Mikkelsen, Tone Melvær Ruud and Dag Sverre Seljebotn are members of the LFI Core Team, “the inner circle” with access to all data. So is also Ingunn K. Wehus, now postdoc at NASA Jet Propulsion Laboratory, as well as our former postdocs Simona Donzella (now at INAF-Milano) and Jussi Väliviita (now at University of Helsinki).
The nominal mission, with two complete scans of the sky, was completed at the end of 2010. Planck then continued its mission with three more scans until the HFI instrument, as expected, ran out of coolant in early 2012 and successfully completed its survey of the early Universe. However, Planck continued surveying the sky using only the LFI instrument until October 2013, this will improve Planck’s final results. In January 2011, the Early Release Point Source Catalogue was released, as well as a large number of scientific non-cosmological papers based on the first 6 months of observations. Since then, a large number of so called “intermediate papers”, also non-cosmological, have been published, while the first cosmological results, based on the first two scans of the sky, were published in 29 papers, together with the data, in March 2013.
The data analysis of Planck is divided in a large number of working groups and core team groups. The Oslo group has a central role in several. Our main scientific interests are the following:
- Power spectrum and cosmological parameters: A very large number or researchers have worked on developing algorithms for extracting the power spectrum from the Planck data, which gets even more difficult with the polarization data. Some of the most important contributions to this effort have come from our group, especially the work led by Hans Kristian Eriksen on the Gibbs sampling method and the code “Commander”. This is one of the main codes used by the Data Processing Centres (DPCs), and is continually fine-tuned when used on the real data.
- Non-gaussianities and large-scale anisotropies: The Oslo group is very central in the Core Team groups for this. Collaborations led by Eriksen and Hansen have already published a large number of papers with results from the WMAP data that have caught widespread attention and very high citation numbers. If it is verified through Planck that such anisotropies are real and of cosmological origin, this will lead to a major revision of cosmology. Inflation also predicts the presence of a small non-Gaussian signal. Detecting or putting limits on this signal will be crucial for understanding the physical processes responsible for the inflationary phase. The group is central in the analysis of the Planck maps for non-Gaussianities, where needlet-based algorithms have been developed in Oslo.
- Map making and component separation: The signal measured by Planck is a combination of the signal from the CMB and a number of other components, of which the most important are caused by emission from gas in the Galaxy. Our group has a prominent role in the effort for devising methods for separating the different components based on spatial and spectral properties (e.g., through Gibbs sampling), and is developing them further as they are confronted with the real data.
Our group has, especially through the work and competences mentioned above, and our comprehensive approach with a very strong attention to the treatment of propagation of systematic effects, a very important role in the analysis of the data from Planck.
The activities are now financed by a grant from the Research Council of Norway: 208016/F50 “Norwegian use of the Planck LFI experiment and QUIET”.
- Anthony J. Banday (CESR, Toulouse)
- Clive Dickinson (University of Manchester)
- Simona Donzelli (INAF-Milano)
- Joanna Dunkley (University of Oxford)
- Pedro Ferreira (University of Oxford)
- Krzysztof M. Gorski (NASA Jet Propulsion Laboratory and Caltech)
- Jeffrey Jewell (NASA Jet Propulsion Laboratory)
- Charles Lawrence (NASA Jet Propulsion Laboratory)
- Michele Liguori (University of Padova)
- Domenico Marinucci (University of Rome “Tor Vergata”)