Galaxy morphology, kinematics and clustering in a hydrodynamic simulation of a �� cold dark matter universe

Abstract

We explore galaxy properties and their link with environment and clustering using a population of ∼1000 galaxies formed in a high-resolution hydrodynamic simulation of the Λ cold dark matter cosmology. At the redshift we concentrate on, z= 1, the spatial resolution is 1.4 proper h−1 kpc and the mass resolution is such that Milky Way sized disc galaxies contain ∼105 particles within their virial radii. The simulations include supermassive black hole accretion and feedback as well as a multiphase model for star formation. Overall, we find that a number of familiar qualitative relationships hold approximately between galaxy properties, for example we observe galaxies as lying between two broad extremes of type, where ‘late’ types tend to be smaller in size, have lower circular velocities, younger stars, higher star formation rates, larger disc to bulge ratios and lower Sersic indices than ‘early types’. We find that as in previous studies of small numbers of resimulated galaxies the stellar component of disc galaxies is not as rotationally supported as in observations. Bulges contain too much of the stellar mass, although exponential discs do have scalelengths compatible with observations, and the stellar mass Tully–Fisher relation at z= 1 is reproduced. The addition of black hole physics to the simulations does not appear to have made a large impact on the angular momentum results compared to these other studies, nor do we find that running an identical simulation with significantly lower mass resolution affects this aspect (although we are unable to test higher mass resolution, which other authors have shown can alleviate the problem). Despite this, we can profitably use the rank order of either disc-to-total ratio, Sersic index, or galaxy age to separate galaxies into morphological classes and examine the density–morphology relation and morphology dependence of clustering. We find that while at redshift z= 0 the well-known preponderance of early types in dense environments is seen, at z= 1 the density–morphology relation becomes flatter and late-type galaxies are even seen to have a higher clustering amplitude than early types.