We now know >400 quasars at a redshift z>6, i.e., observed when the Universe was <1 Gyr old. Their mere presence represents a challenge to our understanding of their formation and early growth of these massive black holes. The host galaxies where they reside harbor copious gaseous reservoirs that are fueling both the black hole growth and intense episodes of star formation. In this talk, I will present on-going studies using ALMA, HST, JWST, VLT and other facilities to characterize two quasar host galaxies at z>6. Multi-line observations set constraints not only on the gas content, but on its physical properties (ionization state, excitation mechanisms, thermodynamics), and allow us to map the multi-phase gas dynamics. These observations allow us to study the baryon cycle in and around the quasar host galaxy, to assess the impact of the luminous quasar on the excitation and photoionization condition of the interstellar medium of the host, and to witness the build-up of the black hole -- host galaxy relations that we observe in the local Universe.

For Zoom connection information, please contact Emanuele Paolo Farina (emanuele.farina_at_noirlab.edu).

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