Near-IR Integral Field Spectroscopy Of High-Redshift Quasar Host Galaxies

In this thesis I exploit near-infrared integral field spectroscopic observations of a sample of high redshift quasars to investigate the properties of their host galaxies and their relation with the nuclear activity. The [OIII]5007 prominent emission line, red- shifted into the near-IR is used to trace the kinematics of the host galaxy of z ∼ 2.5 quasars. One of the most important results is the detection and mapping of prominent outflows driven by the quasar radiation pressure, which were expected by most mod- els of galaxy evolution invoking quasar feedback to quench star formation in massive galaxies. These are among the first maps of quasar-driven outflows at such high red- shift, around the peak of cosmic star formation, where quasar feedback is supposed to be more effective. The inferred outflow rates are very large and can effectively expel most of the gas in the quasar host galaxies on short timescales. The kinetic energies involved in the outflows are also extremely high, and consistent with the models expectations. We also use Hα to trace star formation in the host galaxy. Some quasar host galax- ies show intensive star formation. However, the major discovery is the detection of a suppression of star formation in the regions mostly affected by the quasar driven outflow. This has been regarded as the first direct observational evidence of quasar out- flows quenching star formation in their host galaxies, as predicted by models of galaxy evolution invoking quasar negative feedback. Not all quasars display evidence for out- flows. For some of them the kinematics is dominated by normal galaxy rotation, while some show disordered dynamics indicative of ongoing or recent merging. We also observed a sample of obscured quasars at high redshift, selected in the hard X-rays. For a fraction of them we detect a broad component of the Hα line (redshifted into the near-IR), tracing the reddened Broad Line Region. We have used the broad Hα, along with the hard X-ray emission, to determine the black hole mass hosted in their nuclei. Together with additional data in the literature, and by inferring the stellar masses from broad band photometry, we could for the first time, infer the MBH − Mstar relation for obscured AGNs at high redshift, which represent the bulk of the AGN pop- ulation. We found that high-z obscured AGNs follow the same MBH − Mstar relation as local galaxies. This is in contrast with several previous studies targeting the un- obscured AGN population at high redshift (which easier to investigate, but much less abundant) that have been found to deviate significantly from the local relation, by host- ing over-massive black holes. Our new result suggests either that such previous studies on obscured AGNs were seriously biased in favour of massive black holes, or that there is an evolutionary sequence, in terms of BH-galaxy coevolution, between unobscured and obscured AGNs, but in a sense which is opposite with respect to what expected by most of the previous models.