Accurate measurements of galactic mass
Clusters of galaxies are extremely massive systems that act as powerful gravitational lenses. As peaks of the mass distribution in our Universe, they are extremely sensitive probes in the hands of cosmologists. They focus the light of distant quasars in our direction, making their image appear brighter and larger —just like magnifying lenses do. EU-funded scientists used this effect to peer deeper into the Universe than would otherwise be possible with conventional telescopes. Within the 'Studying gravitational lensing magnification with PAU and other surveys' (LENSMAGPAU) project, they improved the technique of gravitational lensing with the aim of investigating dark matter concentrated in clusters of galaxies. Quasars of known size and shape that are far enough were treated as the source of light. Their image was stretched and magnified by closer clusters of galaxies. The magnification of the source quasars was used to calculate the masses of the galaxy clusters. In addition, LENSMAGPAU scientists examined the change in source colour as a result of dust in the gravitational lenses. Combining these two parameters allowed constraining the mass profiles of clusters of galaxies as well as luminous red galaxies. Specifically, the scientists calculated the mass profiles of clusters of galaxies from the Sloan Digital Sky Survey. The results are consistent with previous analyses of the catalogues, suggesting that systematic errors of lensing magnification were successfully addressed. The new technique is currently being employed on data from the Physics of the Accelerating Universe (PAU), a Spanish collaboration launched in 2014 to explore the nature of dark matter in the Universe. Since dark matter outweighs 'normal' matter by a factor of six, it is thought to be responsible for almost all the gravitational lensing.
Keywords
Galactic mass, gravitational lensing, galaxies, quasars, dark matter
