Physics Department Seminar: A deviation from the cosmological constant model in the Hubble diagram of high-redshift quasars
14/5/2019 ore 15:00
Sala Consiglio, Dip. Fisica
A DEVIATION FROM THE COSMOLOGICAL CONSTANT MODEL IN THE HUBBLE DIAGRAM OF HIGH-REDSHIFT QUASARS
Dr. Guido Risaliti Università di Firenze
"The non-linear X-ray to UV luminosity relation in quasars can be used to turn quasars into standard candles. This opens the way to a new branch of observational cosmology, based on a Hubble diagram of quasars up to redshift z>6. Our analysis of a new sample of luminous z~3 quasars, combined with
the data available in public archives, shows that the *intrinsic* dispersion of the relation is remarkably small (lower than 0.1 dex), while most of the *observed* dispersion (~0.35 dex) is due to measurements errors and selection biases.
The application of this method to the available quasars with X-ray and UV flux measurements allowed us to build a Hubble diagram of quasars up to z~6.
While this diagram is in agreement with that of supernovae -and with the concordance model of cosmology- up to z~1.5, significant deviations emerge at higher redshifts, suggesting a possible redshift evolution of the dark energy component."