Adrianne Slyz

Abstract:

State-of-the-art hydrodynamical simulations show that gas inflow through the virial sphere of dark matter halos is focused (i.e. has a preferred inflow direction), consistent (i.e. its orientation is steady in time) and amplified (i.e. the amplitude of its advected specific angular momentum increases with time). We explain this to be a consequence of the dynamics of the cosmic web within the neighbourhood of the halo, which produces steady, angular momentum rich, filamentary inflow of cold gas. On large scales, the dynamics within neighbouring patches drives matter out of the surrounding voids, into walls and filaments before it finally gets accreted onto virialised dark matter halos. As these walls/filaments constitute the boundaries of asymmetric voids, they acquire a net transverse motion, which explains the angular momentum rich nature of the later infall which comes from further away. We conjecture that this large-scale driven consistency explains why cold flows are so efficient at building up high redshift thin discs from the inside out.

Abstract:

The interstellar medium (ISM) in galaxies is multiphase and cloudy, with stars forming in the very dense, cold gas found in Giant Molecular Clouds (GMCs). Simulating the evolution of an entire galaxy, however, is a computational problem which covers many orders of magnitude, so many simulations cannot reach densities high enough or temperatures low enough to resolve this multiphase nature. Therefore, the formation of GMCs is not captured and the resulting gas distribution is smooth, contrary to observations. We investigate how star formation (SF) proceeds in simulated galaxies when we obtain parsec-scale resolution and more successfully capture the multiphase ISM. Both major mergers and the accretion of cold gas via filaments are dominant contributors to a galaxy's total stellar budget and we examine SF at high resolution in both of these contexts. © 2011 International Astronomical Union.

Abstract:

Observed clusters of galaxies essentially come in two flavors: non cool core clusters characterized by an isothermal temperature profile and a central entropy floor, and cool-core clusters where temperature and entropy in the central region are increasing with radius. Using cosmological resimulations of a galaxy cluster, we study the evolution of its intracluster medium (ICM) gas properties, and through them we assess the effect of different (sub-grid) modelling of the physical processes at play, namely gas cooling, star formation, feedback from supernovae and active galactic nuclei (AGN). More specifically we show that AGN feedback plays a major role in the pre-heating of the proto-cluster as it prevents a high concentration of mass from collecting in the center of the future galaxy cluster at early times. However, AGN activity during the cluster's later evolution is also required to regulate the mass flow into its core and prevent runaway star formation in the central galaxy. Whereas the energy deposited by supernovae alone is insufficient to prevent an overcooling catastrophe, supernovae are responsible for spreading a large amount of metals at high redshift, enhancing the cooling efficiency of the ICM gas. As the AGN energy release depends on the accretion rate of gas onto its central black hole engine, the AGN responds to this supernova enhanced gas accretion by injecting more energy into the surrounding gas, and as a result increases the amount of early pre-heating. We demonstrate that the interaction between an AGN jet and the ICM gas that regulates the growth of the AGN's BH, can naturally produce cool core clusters if we neglect metals. However, as soon as metals are allowed to contribute to the radiative cooling, only the non cool core solution is produced.