  We investigate the formation and properties of galaxies hosting z~6 quasars,
in the gigaparsec scale cosmological hydrodynamical simulation: MassiveBlack,
which includes a self-consistent model for star formation, black hole accretion
and associated feedback. We show that the MassiveBlack reproduces current
estimates of the galaxy stellar mass function z=5, 6. We find that quasar hosts
in the simulation are compact gas rich systems with high star formations rates
of SFR ~ 100-1000 Msun/yr consistent with observed properties of Sloan quasar
hosts in the redshift range 5.5 < z < 6.5. We show that the star-forming gas in
these galaxies predominantly originates from high density cold streams which
are able to penetrate the halo and grow the galaxy at the center. MassiveBlack
predicts a deviation from the local Mbh-sigma and Mbh-Mstar relation implying
that black holes are relatively more massive for a given stellar host at these
redshifts.

Cosmology and Nongalactic Astrophysics