Interpreting New Galaxy Large-scale Structure Measurements and the Galaxy–Halo Connection
The galaxy distribution in the joint space of stellar mass and star formation rate (SFR) is observed to be bimodal, with distinct star-forming (high SFR) and quiescent (low SFR) populations across many orders of magnitude in stellar mass. The absence of a significant population of intermediate-stage galaxies implies that galaxies tend to cease star formation and become quiescent relatively rapidly, and the physical origins of this rapid quenching are an open question in the field of galaxy evolution.
Recent progress in cosmological simulations of dark matter structure evolution, as well as in statistical modeling of how galaxies inhabit dark matter halos, suggest a nuanced coevolutionary relationship between galaxies and the dark matter halos galaxies reside in (the "galaxy–halo connection"), in which the statistical galaxy content of a halo depends on more than halo mass. One class of these galaxy–halo connection models are those that incorporate galaxy assembly bias, a general term for the dependence of galaxy properties on halo properties other than mass. For example, distinct stellar-to-halo mass relations for star-forming and quiescent central galaxies is a form of galaxy assembly bias that could manifest as an anticorrelation of galaxy SFR with clustering amplitude, if the trend is independent of stellar (or halo) mass.
In this dissertation we present the first measurements of galactic conformity, or the tendency of neighboring galaxies to share the star formation properties of an adjacent central galaxy, on two-halo scales beyond the local universe (to z~1). We then measure the clustering of isolated galaxies as a proxy for central galaxies, separately for star-forming and quiescent galaxies, to test predictions of galaxy–halo models reflecting galaxy assembly bias. Finally, we measure the joint dependence of clustering on stellar mass and SFR. With mock galaxy catalogs derived from simulations and an empirical galaxy evolution model we quantify and compensate for the effects of systematic biases on these measurements. A parallel theme of this dissertation is demonstrating how existing galaxy surveys beyond the local universe are at the cusp of probing the volumes needed for statistically significant tests of theoretical predictions of various models of galaxy evolution.