The host dark matter haloes of the first quasars

Understand

If $z > 6$ quasars reside in rare, massive haloes, $\Lambda$CDM cosmology predicts they should be surrounded by an anomalously high number of bright companion galaxies.

• Here I show that these companion galaxies should also move unusually fast.
• Using a new suite of cosmological, `zoom-in' hydrodynamic simulations, I present predictions for the velocity distribution of quasar companion galaxies and its variation with quasar host halo mass at $z \, = \, 6$.
• Satellites accelerate as they approach the quasar host galaxy, producing a line-of-sight velocity profile that broadens with decreasing distance to the quasar host galaxy.