Chiara Mazzucchelli

Chiara Mazzucchelli (Italy)

mazzucchelli @

The Physical Properties of High Redshift Quasars

Quasars are active extragalactic sources whose emission is powered by accretion of material onto a central black hole. Quasars have been observed at high redshifts (z>5.5): thanks to their intrinsic high luminosities, they are unique probes of the early Universe (1 Gyr from the Big Bang), at the end of the epoch of reionization. These high-redshift quasars already host massive black holes (MBH >10^9 Msun): their characterization allows us to put stringent limits on the mechanism of black hole growth and accretion. Since they appeared well-evolved system, these quasars are believed to reside in the high-density peaks of the dark matter distribution, which will evolve into nowadays most massive clusters: therefore, they would be ideal signposts of the first protoclusters.
In the present thesis, I plan to increase the sample of known high-redshift quasars, aiming for redshift limits never achieved before (z>7.5-8). This will allow us to investigate the physics of the Universe even further into the epoch of reionization, where the first generations of stars and galaxies started to shine. I will take advantage of multi-wavelength information obtained by cross-matching a variety of wide-area optical/NIR/MIR surveys (i.e. Pan-STARRS, UKIDSS, WISE). In order to identify new high-redshift quasars, I will adopt some color-color criteria, as done in the literature so far, as well as a SED fitting technique, specifically designed to properly take into account and fully exploit the multi-dimensional constraints from the available photometric information. This process will us allow to down-select candidates for dedicated follow-up photometric and spectroscopic observations, aiming at removing possible contaminants (i.e. mainly L and T stars). The resulting sample, will constituent the foundation for a number of studies of the early Universe. In particular, I will investigate the relation between quasars and their galactic environment, in order to assess if they resides in important cosmic density peaks, as expected by the present models of structure formation.

Supervisor: Fabian Walter (MPIA)

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