| Current galaxy formation theory still struggles to explain many essential galaxy properties. This thesis addresses these problems in the context of the interplay between baryons and dark matter in the concordance cosmological model. In the first part, we investigate galaxy abundance and scaling relations using a compilation of observational data along with large-scale cosmological simulations of dark matter (DM). We find that the standard cosmological model, in conjunction with halo abundance matching (HAM) and simple dynamical corrections, fits all basic statistics of galaxies more massive than the Large Magellanic Cloud (LMC). This zero-parameter model predicts the observed luminosity-velocity relation of early-and late-type galaxies, as well as the clustering of bright galaxies and the observed abundance of galaxies as a function of circular velocity. However, we find that all DM halos more massive than the LMC are much more abundant than the galaxies they host. Motivated by the model's shortcomings, in the second part we study the effect of baryons on galaxy formation using numerical simulations that include gas physics. We implement a model of star formation (SF) and stellar feedback based directly on observations of star-forming regions, where stellar feedback from massive stars includes radiation pressure, photoheating, supernovae, and stellar winds. We find that stellar radiation has a strong effect at z > 1, where it efficiently suppresses SF by dispersing cold and dense gas, preventing runaway growth of the stellar component, and yielding rising SF histories that reproduce many observations. Stellar feedback produces bulgeless discs with rotation curves and baryon fractions in excellent agreement with data. Feedback-driven blowouts reduce the central DM density of a dwarf, relieving tension between ACDM and observations. Based on these results, we begin to characterize the baryon cycle of galaxies and its imprint on studies of the circumgalactic medium (CGM). We find that feedback has a large impact on the exchange of gas and metals between the galaxy and the halo. This is evidenced in the spatial distribution of various gas phases and in the kinematics of accretion and outflows. We conclude that synergy between simulations and absorption-line studies is essential for disentangling the physics of galaxy formation in the context of ACDM. |
