Cosmology is a research field in astronomy that aims to unravel the structure and evolution of the universe as well as its contents. The modern surveys focus on specific parts in the evolution of the Universe (e.g. cosmological inflation, microwave background radiation (CMB), large-scale structures, intergalactic medium, galaxies, etc.) and try to understand them and their role in the evolution of the Universe.
At the turn of the century large surveys were primarily focused on the cosmological microwave background (WMAP, VSA, Boomerang, …) and galaxies (2dFGRS, SDSS, …) which answered many cosmological questions of the previous century. The new generation surveys are mostly oriented towards the physical phenomena that would put very tight constraints on various theoretical predictions (polarization of the CMB, weak gravitational lensing, absorption in the intergalactic medium).
Figure (top): Shows the distribution of the matter density in the numerical simulation Millenium The density field was computed with the TreeSPH code Gadget. The plot shows the slice of order 400 Mpc through the entire simulation. The absorption in the intergalactic medium is mostly due to the filamentary structures around the central density peak (a cluster of galaxies).
At the Faculty of Mathematics and Physics (FMF) we are studying the absorption in the intergalactic medium. Because the intergalactic medium (IGM) consists mostly of hydrogen (which is the most common element in the universe), the absorption is primarily due to the electronic transition in the hydrogen atom (from n=1 to n=2 state). Because the universe is expanding, the wavelengths of the photons from the distant quasar are stretching on their way to the Earth and at different distances from the Earth photons with different emitted (initial) wavelengths will be absorbed in the IGM, leaving a distinct feature in the spectrum of a quasar. This characteristic structure of absorption lines is called the Lyman alpha forest and is found bluewards of the Lyman alpha emission in the quasar spectrum.
By studying the statistical properties of those structures one can constrain the power spectrum of the matter distribution in the IGM. The matter power spectrum measurements can then be further used to put tighter constraints on many different physical parameters: light neutrino masses (light elemental particles without electric charge), cosmological inflation and re-ionization.
Figure (bottom): Shows a typical quasar spectrum. Bluewards of the Lyman alpha emission line is the Lyman alpha forest colored in green. The data are from the large galaxy survey SDSS (Sloan Digital Sky Survey). The Lyman alpha absorption in the IGM is due to the neutral hydrogen between the Earth and the distant quasar.