%0 Generic
%A Mazzucchelli, Chiara
%D 2018
%F heidok:25125
%R 10.11588/heidok.00025125
%T The Physical Properties and Cosmic Environments of Quasars in the First Gyr of the Universe
%U https://archiv.ub.uni-heidelberg.de/volltextserver/25125/
%X Luminous quasars at redshift z >6, i.e. <1 Gyr after the Big Bang, are formidable probes of  the early universe, at the edge of the Epoch of Reionization. These sources are predicted  to be found in high–density peaks of the dark matter distribution at that time, surrounded  by overdensities of galaxies. In this thesis, we present a search for and study of the most  distant quasars, from the properties of their innermost regions, to those of their host galaxies  and of their Mpc–scale environments. We search for the highest redshift quasars in the  Panoramic Survey Telescope and Rapid Response System 1 (Pan-STARRS1, PS1), discovering  six new objects at z >6.5. Using optical/near–infrared spectroscopic data, we perform a homogeneous  analysis of the properties of 15 quasars at z> 6.5. In short : 1) The majority of z >6.5  show large blueshifts of the broad CIV 1549 Å emission line, suggesting the presence of strong  winds/outflows; 2) They already host supermassive black holes (M_BH = 0.3 - 5 x 10^9 M_sun) in their  centers, which are accreting at a rate comparable to a luminosity–matched sample at z =1-3)  No evolution of the Fe II/MgII abundance ratio with cosmic time is observed; 4) The sizes of  their surrounding ionized bubbles weakly decrease with redshift. We present new millimeter  observations of the dust continuum and of the [CII] 158 mm emission line (one of the main  coolant of the intergalactic medium) in the host galaxies of four quasars, providing new accurate  redshifts and [CII]/infrared luminosities. We study the Mpc–scale environment of a z =5.7  quasar, via observations with broad– and narrow–band filters. We recover no overdensities  of galaxies. Among the potential explanations for these findings, are that the ionizing radiation  from the quasar prevents galaxy formation, the sources in the fields are dust–obscured,  or quasars do not live in the most massive dark matter halos. Finally, we report sensitive  optical/near–infrared follow–up observations of gas–rich companion galaxies to four quasars  at z >6, firstly detected with the Atacama Large Millimeter Array (ALMA).With the exception  of one source, we detect no emission from the stellar population of these galaxies. Our limits on  their stellar masses (< 10^10 M_sun) and unobscured star formation rates (<few M_sun yr^1) suggest  that the companions are highly dust obscured and/or harboring a modest stellar content. In  synthesis, in this thesis we show the large range of parameters of the most distant quasars, and  the variety of their environments, with the aim of shading light on massive galaxy and black  hole formation in the first Gyr of the universe.