The Formation of Galaxies Hosting z~6 Quasars

TL;DR

This paper uses a cosmological hydrodynamical simulation to study the formation and properties of galaxies hosting z~6 quasars, revealing their gas-rich, high star formation rate nature and deviations in black hole scaling relations.

Contribution

It demonstrates that the MassiveBlack simulation accurately reproduces galaxy stellar mass functions at z=5-6 and provides insights into the gas accretion and black hole growth in early quasar hosts.

Findings

Quasar hosts are compact, gas-rich systems with high star formation rates.

Star-forming gas mainly comes from high-density cold streams.

Black holes are more massive relative to their host galaxies than in the local universe.

Abstract

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.