LSS - discovering the world of X-ray astronomy...
Though the story of X-ray astronomy begun only some forty years ago, X-rays have been discovered in 1895 by Wilhelm Roentgen. Among the most spectacular X-ray pictures obtained by Roentgen was that of the bones of his wife's hand. For the first time men were able to look inside the human body.
The very first cosmic X-ray source has been identified in 1966 as a star.
The main interest of X-ray domain astronomy is that X-rays originate in the universe from regions under extreme conditions, from plasma with temperatures up to billions of degrees, and from the interactions of highly energetic electrons with magnetic and photon fields (e.g supernova remnants, star coronae, accretion disk around super massive black holes,...). Studying cosmic objects in X-rays gives insights in the physical processes, that often cannot be achieved observing in other wave bands.
Active galactic nuclei (AGN) within the large scale structures
We use redshift and Hubble Law to get distances of galaxies. Combined with their measured flux, we infer their luminosity. A class of galaxies have an extremely luminous center (nucleus). These are the active galactic nuclei (AGN), among which the quasars have the highest intrinsic luminosity, which can be as high as 1000 times the luminosity of a typical galaxy. The huge luminosity of AGN is likely produced by accretion of matter around super massive black holes.
One of the most important discoveries of the early days of X-ray astronomy was that X-ray emission is an extremely common property of AGN and that much of the observed luminosity produced in AGN is radiated in the X-ray domain. That is the reason why X-ray surveys are much more efficient to unveil AGN than optical or infrared surveys. Our research group is involved in the XMM-LSS survey.
By Measuring the redshifts of galaxies and using the Hubble Law, we can also determine their distances and therefore map out the Large Scale Structure of the Universe.
Galaxies and clusters define "bubbles" of size ~ 30 Mpc (100 million light years). Great voids with few galaxies surounded by walls and filaments of superclusters.
The most recent papers by the Liège AEOS group dedicated to Large Scale Structure studies are listed hereafter: