We explore the connections between the evolving galaxy and AGN populations. We present a simple phenomenological model that links the evolving galaxy mass function and the evolving quasar luminosity function, which makes specific and testable predict
ions for the distribution of host galaxy masses for AGN of different luminosities. We show that the $phi^{*}$ normalisations of the galaxy mass function and of the AGN luminosity function closely track each other over a wide range of redshifts, implying a constant duty cycle of AGN activity. The strong redshift evolution in the AGN $L^*$ can be produced by either an evolution in the distribution of Eddington ratios, or in the $m_{bh}/m_{*}$ mass ratio, or both. To try to break this degeneracy we look at the distribution of AGN in the SDSS ($m_{bh},L$) plane, showing that an evolving ratio $m_{bh}/m_{*} propto (1+z)^2$ reproduces the observed data and also reproduces the local relations which connect the black hole population with the host galaxies for both quenched and star-forming populations. We stress that observational studies that compare the masses of black holes in active galaxies at high redshift with those in quiescent galaxies locally will always see much weaker evolution. Evolution of this form would produce, or could be produced by, a redshift-independent $m_{bh} - sigma$ relation and could explain why the local $m_{bh} - sigma$ relation is tighter than $m_{bh} - m_{*}$ even if $sigma$ is not directly linked to black hole growth. Irrespective of the evolution of $m_{bh}/m_{*}$, the model reproduces both the appearance of downsizing and the so-called sub-Eddington boundary without any mass-dependence in the evolution of black hole growth rates.
The origin and growth of magnetic fields in galaxies is still something of an enigma. It is generally assumed that seed fields are amplified over time through the dynamo effect, but there are few constraints on the timescale. It has recently been dem
onstrated that field strengths as traced by rotation measures of distant quasars are comparable to those seen today, but it was unclear whether the high fields were in the exotic environments of the quasars themselves or distributed along the line of sight. Here we demonstrate that the quasars with strong MgII absorption lines are unambiguously associated with larger rotation measures. Since MgII absorption occurs in the haloes of normal galaxies along the sightline to the quasars, this association requires that organized fields of surprisingly high strength are associated with normal galaxies when the Universe was only about one-third of its present age.
