Physical Models of Galaxy Formation in a Cosmological Framework

Abstract

Modeling galaxy formation in a cosmological context presents one of the greatest challenges in astrophysics today, due to the vast range of scales and numerous physical processes involved. Here we review the current status of models that employ two leading techniques to simulate the physics of galaxy formation: semi-analytic models and numerical hydrodynamic simulations. We focus on a set of observational targets that describe the evolution of the global and structural properties of galaxies from roughly Cosmic High Noon (z ∼ 2-3) to the present. Although minor discrepancies remain, overall, models show remarkable convergence between different methods and make predictions that are in qualitative agreement with observations. Modelers seem to have converged on a core set of physical processes that are critical for shaping galaxy properties. This core set includes cosmological accretion, strong stellar-driven winds that are more efficient at low masses, black hole feedback that preferentially suppresses star formation at high masses, and structural and morphological evolution through merging and environmental processes. However, all cosmological models currently adopt phenomenological implementations of many of these core processes, which must be tuned to observations. Many details of how these diverse processes interact within a hierarchical structure formation setting remain poorly understood. Emerging multi-scale simulations are helping to bridge the gap between stellar and cosmological scales, placing models on a firmer, more physically grounded footing. Concurrently, upcoming telescope facilities will provide new challenges and constraints for models, particularly by directly constraining inflows and outflows through observations of gas in and around galaxies.

The relationship between star formation activity and galaxy structural properties in CANDELS and a semi-analytic model

“…The rate at which this gas can cool is determined by a simple spherical cooling flow model (see Somerville et al (2008) for details) which approximates the transition from "cold flows", where cold gas streams into the halo along dense filaments without being heated, to "hot flows", where gas is shock heated on its way in, forming a diffuse hot gas halo before cooling (Birnboim & Dekel 2003;Kereš et al 2005;Dekel & Birnboim 2006). In this way, virial shock heating is included in our SAM, although many studies show that this effect alone is not enough to produce the observed population of massive quiescent galaxies (Somerville & Davé 2015, and references therein).…”

The impact of galactic properties and environment on the quenching of central and satellite galaxies: a comparison between SDSS, Illustris and L-Galaxies

“…Observationally, satellites in general depend on both intrinsic and environmental parameters for their quenching, whereas centrals depend primarily only on intrinsic properties (e.g., Peng et al 2012). In many simulations and models, the quenching of central galaxies is governed primarily by AGN feedback and the quenching of satellite galaxies is governed primarily by environmental processes, such as, e.g., strangulation or stripping (e.g., Guo et al 2011;Vogelsberger et al 2014a,b;Henriques et al 2015;Schaye et al 2015;Peng et al 2015;Somerville et al 2015).…”

The Properties of the Circumgalactic Medium in Red and Blue Galaxies: Results From the Cos-Gass+cos-Halos Surveys

“…There, it condenses into neutral and then molecular gas, some of which is then converted into stars. Young stars, in turn, drive strong winds, outflows, and radiation that deposit mass, metals, energy, and momentum to the CGM, thus significantly influencing its properties (see review by Somerville & Davé 2015;Fielding et al 2016, and references therein). These linked processes are commonly termed the baryon cycle.…”