0 Assigned ID: 267 ----- Attempting Submission 1 (Thu Mar 05 18:17:03 GMT 2020) ----- The origin of disk galaxies is a central problem in galaxy formation. In the prevailing paradigm, disks inherit angular momentum (AM) from their host halos and AM conservation sets disk sizes. However, deep HST surveys have revealed that disk galaxies are a recent phenomenon: disks start to appear in massive galaxies only around z~2 and disk settling in lower-mass galaxies is delayed until even later. Since halo spins do not depend on mass or redshift, these observations directly contradict the standard model. In the past few years, high-resolution cosmological simulations have produced predictions qualitatively consistent with observations, with simulated galaxies experiencing a switch to well-ordered disks only as they approach L^*. Intriguingly, the simulations predict that disk formation is accompanied by important changes in star formation and galactic wind properties: SFRs switch from highly bursty to time steady, and galactic winds (which are ubiquitous at high z) are strongly suppressed. This project will use a large suite of simulations from the FIRE project to systematically test different models for disk formation. These models include recently proposed ideas on the failure of stellar feedback in early galaxies, as well as connections between halo gas and disk physics (including AM exchanges). We will in particular test in detail a new model for disk formation based on the development of hot atmospheres around massive galaxies, which can simultaneously explain the different observed transitions. We will produce directly testable predictions, including mock HST and JWST images/IFU data, indicators of SFR variability, and diagnostics of ISM kinematics and winds. PI Faucher-Giguere is a founder and core developer of the FIRE simulation project. He developed models for several of the core physical processes included in the simulations, such as the cosmic UV background, supernova feedback, and supermassive black holes. Faucher-Giguere has extensive experience with the GIZMO simulation code. Along with students and postdocs, Faucher-Giguere has led most of the studies of the circumgalactic medium using FIRE simulations published so far, including particle tracking (e.g., Faucher-Giguere et al. 2015, 2016; Angles-Alcazar et al. 2017a; Hafen et al. 2017, 2019ab). Faucher-Giguere developed the analytic theory for star formation regulation and disk settling (Faucher-Giguere et al. 2013; Faucher-Giguere 2018) that the proposed analysis would test using cosmological simulations. Faucher-Giguere also has extensive experience with radiative transfer modeling and the CHIMES chemistry network (e.g., Faucher-Giguere et al. 2010; Richings & Faucher-Giguere 2018ab). Thus, the PI and his group have extensive expertise in all the main halo gas, ISM, and stellar feedback processes to be investigated. Galaxies 0 Regular false false false true false SUPPORTED