Speaker
Description
A tight non-linear relation between the X-ray and the optical-ultraviolet luminosity has been observed in AGN over 5 orders of magnitude and up to high redshift.
This suggests a coupling between the disk, emitting the primary radiation in the UV band, and the hot corona emitting in the X-ray.
In this work, we have studied the $L_X-L_{UV}$ relation for a sample of high-redshift ($z>4$) quasars, selected on the basis of their spectral properties and the quality of the available observations in both X-ray and optical/UV bands.
The relation shows no-evidence of evolution with redshift, which indicates a universal physical mechanism regulating the energy transfer process in the inner regions, and the observed dispersion is lower than in previous estimates.
The non-linearity of the relation provides a new, powerful way to estimate the absolute luminosity, turning quasars into a new class of standard candles that can provide an important contribution in the determination of the cosmological parameters, probing cosmological time not achievable with other observational methods.
| Affiliation | Dipartimento di Fisica e Astronomia, Università di Bologna |
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