Search and Study of Blazars in the early Universe
PhD thesis by Silvia Belladitta , Matr. 733846
The aim of this thesis is to identify and characterize blazars at z>4, to provide more constraints on
the properties of high-z radio-loud (RL) Active Galactic Nuclei (AGNs) population.
Blazars are RL AGNs with relativistic jets pointing towards the Earth. The discovery of high-z
blazars ensures the census, free from obscuration effects, of supermassive black holes (SMBHs)
hosted by RL AGNs in the early Universe. Indeed for each observed blazar we expect to find ~2\u3932
(where \u393 is the bulk Lorentz factor of the jet) RL AGNs, whose jets point in other directions, with
the same properties (e.g. MBH, Lradio, etc.).
By combining different radio/optical/infrared surveys available to date and by using the dropout
method I built up a statistically complete sample (21 objects) of blazars at 4<5.5, and I
discoverer new (3) blazars at z>5. One of these, at z=6.1, is also the most distant blazar ever
discovered. With these sources I increased by 50% the number of blazars known to date at z>4.
I performed a multi wavelength analysis of the properties of all these sources (from radio to X-ray
bands) and I compared them to both RL and radio-quiet (RQ, AGNs without relativistic jets) AGNs
at similar redshift. The blazars reported in this thesis are all powerful X-ray sources, have a similar
radio spectrum (flat or peaked) and host SMBHs with MBH>108M 99.
The presence of such massive objects at high-z requires possible super-eddington accretion
episodes for the seed black holes growth
