The changing circumgalactic medium over the last 10 Gyr I: physical and
  dynamical properties
  We present an analysis of the physical and dynamical states of two sets of
EAGLE zoom simulations of galaxy haloes, one at high redshift ($z=2-3$) and the
other at low redshift ($z=0$), with masses of $\approx 10^{12} M_{\odot}$. Our
focus is how the circumgalactic medium (CGM) of these $L^*$ star-forming
galaxies change over the last 10 Gyr. We find that the high-$z$ CGM is almost
equally divided between the "cool" ($T<10^5$ K) and "hot" ($T\geq 10^5$ K)
phases, while the low-$z$ hot CGM phase contains $5\times$ more mass. The
high-$z$ hot CGM contains 60% more metals than the cool CGM, while the low-$z$
cool CGM contains 35% more metals than the hot CGM content. The metals are
evenly distributed radially between the hot and cool phases throughout the
high-$z$ CGM. At high $z$, the CGM volume is dominated by hot outflows, cool
gas is mainly inflowing, but cool metals are flowing outward. At low $z$, the
cool metals dominate the interior and the hot metals are more prevalent at
larger radii. The low-$z$ cool CGM has tangential motions consistent with
rotational support out to $0.2 R_{200}$, often exhibiting $r \approx 40$ kpc
disc-like structures. The low-$z$ hot CGM has several times greater angular
momentum than the cool CGM, and a more flattened radial density profile than
the high-$z$ hot CGM. This study verifies that, just as galaxies demonstrate
significant evolutionary stages over cosmic time, the gaseous haloes
surrounding them also undergo considerable changes of their own both in
physical characteristics of density, temperature and metallicity, and dynamic
properties of velocity and angular momentum.
