Introducing the Illustris Project: the evolution of galaxy populations
  across cosmic time
  We present an overview of galaxy evolution across cosmic time in the
Illustris Simulation. Illustris is an N-body/hydrodynamical simulation that
evolves 2*1820^3 resolution elements in a (106.5Mpc)^3 box from cosmological
initial conditions down to z=0 using the AREPO moving-mesh code. The simulation
uses a state-of-the-art set of physical models for galaxy formation that was
tuned to reproduce the z=0 stellar mass function and the history of the cosmic
star-formation rate density. We find that Illustris successfully reproduces a
plethora of observations of galaxy populations at various redshifts, for which
no tuning was performed, and provide predictions for future observations. In
particular, we discuss (a) the buildup of galactic mass, showing stellar mass
functions and the relations between stellar mass and halo mass from z=7 to z=0,
(b) galaxy number density profiles around massive central galaxies out to z=4,
(c) the gas and total baryon content of both galaxies and their halos for
different redshifts, and as a function of mass and radius, and (d) the
evolution of galaxy specific star-formation rates up to z=8. In addition, we
(i) present a qualitative analysis of galaxy morphologies from z=5 to z=0, for
the stellar as well as the gaseous components, and their appearance in HST mock
observations, (ii) follow galaxies selected at z=2 to their z=0 descendants,
and quantify their growth and merger histories, and (iii) track massive z=0
galaxies to high redshift and study their joint evolution in star-formation
activity and compactness. We conclude with a discussion of several
disagreements with observations, and lay out possible directions for future
research.
