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The circumgalactic medium (CGM) plays a pivotal role in regulating gas flows around galaxies and thus shapes their evolution. However, the details of how galaxies and their CGM co-evolve remain poorly understood. We present a new time-dependent two-zone model that self-consistently tracks not just mass and metal flows between galaxies and their CGM but also the evolution of the global thermal and turbulent kinetic energy of the CGM. Our model accounts for heating and turbulence driven by both supernova winds and cosmic accretion as well as radiative cooling, turbulence dissipation, and halo outflows due to CGM overpressurization. We demonstrate that, depending on parameters, the CGM can undergo a phase transition (``thermalization'') from a cool, turbulence-supported phase to a virial-temperature, thermally-supported phase. This CGM phase transition is largely determined by the ability of radiative cooling to balance heating from supernova winds and turbulence dissipation. We perform an initial calibration of our model to the FIRE-2 cosmological hydrodynamical simulations and show that it is remarkably successful in reproducing the baryon cycles of the simulated galaxies and their CGM. In particular, we find that, for these parameters, the phase transition occurs at high-redshift in ultrafaint progenitors and at low redshift in classical $M_{\rm vir}\sim10^{11}M_{\odot}$ dwarfs, while Milky Way-mass halos undergo the transition at $z\approx0.5$, in agreement with the simulations. We discuss the ways in which our model is complementary to existing approaches for modeling the CGM--galaxy connection and possible future directions., Comment: Submitted to ApJ, main body is 28 pages with 15 figures, comments welcome

Increasingly, uncertainties in predictions from galaxy formation simulations (at sub-Milky Way masses) are dominated by uncertainties in stellar evolution inputs. In this paper, we present the full set of updates from the FIRE-2 version of the Feedback In Realistic Environments (FIRE) project code, to the next version, FIRE-3. While the transition from FIRE-1 to FIRE-2 focused on improving numerical methods, here we update the stellar evolution tracks used to determine stellar feedback inputs, e.g. stellar mass-loss (O/B and AGB), spectra (luminosities and ionization rates), and supernova rates (core-collapse and Ia), as well as detailed mass-dependent yields. We also update the low-temperature cooling and chemistry, to enable improved accuracy at $T \lesssim 10^{4}\,$K and densities $n\gg 1\,{\rm cm^{-3}}$, and the meta-galactic ionizing background. All of these synthesize newer empirical constraints on these quantities and updated stellar evolution and yield models from a number of groups, addressing different aspects of stellar evolution. To make the updated models as accessible as possible, we provide fitting functions for all of the relevant updated tracks, yields, etc, in a form specifically designed so they can be directly 'plugged in' to existing galaxy formation simulations. We also summarize the default FIRE-3 implementations of 'optional' physics, including spectrally-resolved cosmic rays and supermassive black hole growth and feedback., 26 pages, 12 figures. Submitted to MNRAS. Comments welcome

The shape and orientation of dark matter (DM) halos are sensitive to the micro-physics of the DM particle, yet in many mass models, the symmetry axes of the Milky Way's DM halo are often assumed to be aligned with the symmetry axes of the stellar disk. This is well-motivated for the inner DM halo but not for the outer halo. We use zoomed cosmological-baryonic simulations from the Latte suite of FIRE-2 Milky Way-mass galaxies to explore the evolution of the DM halo's orientation with radius and time, with or without a major merger with a Large Magellanic Cloud (LMC) analog, and when varying the DM model. In three of the four CDM halos we examine, the orientation of the halo minor axis diverges from the stellar disk vector by more than 20 degrees beyond about 30 galactocentric kpc, reaching a maximum of 30--90 degrees depending on the individual halo's formation history. In identical simulations using a model of self-interacting DM with $\sigma = 1 \, \mathrm{cm}^2 \, \mathrm{g}^{-1}$, the halo remains aligned with the stellar disk out to $\sim$200--400 kpc. Interactions with massive satellites ($M \gtrsim 4 \times 10^{10} \, \rm{M_\odot}$ at pericenter; $M \gtrsim 3.3 \times 10^{10} \, \rm{M_\odot}$ at infall) affect the orientation of the halo significantly, aligning the halo's major axis with the satellite galaxy from the disk to the virial radius. The relative orientation of the halo and disk beyond 30 kpc is a potential diagnostic of SIDM if the effects of massive satellites can be accounted for., Comment: Submitted to ApJ, 19 pages, 12 figures, 3 tables

Low-mass galaxies are highly susceptible to environmental effects that can efficiently quench star formation. We explore the role of ram pressure in quenching low-mass galaxies ($M_{*}\sim10^{5-9}\,\rm{M}_{\odot}$) within 2 Mpc of Milky Way (MW) hosts using the FIRE-2 simulations. Ram pressure is highly variable across different environments, within individual MW haloes, and for individual low-mass galaxies over time. The impulsiveness of ram pressure -- the maximum ram pressure scaled to the integrated ram pressure prior to quenching -- correlates with whether a galaxy is quiescent or star-forming. The time-scale between maximum ram pressure and quenching is anticorrelated with impulsiveness, such that high impulsiveness corresponds to quenching time-scales $, 12 pages, 10 figures, + appendix

We examine the thermodynamic state and cooling of the low-z circumgalactic medium (CGM) in five FIRE-2 galaxy formation simulations of Milky Way-mass galaxies. We find that the CGM in these simulations is generally multiphase and dynamic, with a wide spectrum of largely non-linear density perturbations sourced by the accretion of gas from the intergalactic medium (IGM) and outflows from both the central and satellite galaxies. We investigate the origin of the multiphase structure of the CGM with a particle-tracking analysis and find that most of the low-entropy gas has cooled from the hot halo as a result of thermal instability triggered by these perturbations. The ratio of cooling to free-fall time-scales tcool/tff in the hot component of the CGM spans a wide range of ∼1−100 at a given radius but exhibits approximately constant median values of ∼5−20 at all radii 0.1Rvir < r < Rvir. These are similar to the ≈10−20 value typically adopted as the thermal instability threshold in ‘precipitation’ models of the ICM. Consequently, a one-dimensional model based on the assumption of a constant tcool/tff and hydrostatic equilibrium approximately reproduces the number density and entropy profiles of each simulation but only if it assumes the metallicity profile and temperature boundary condition taken directly from the simulation. We explicitly show that the tcool/tff value of a gas parcel in the hot component of the CGM does not predict its probability of subsequently accreting on to the central galaxy. This suggests that the value of tcool/tff is a poor predictor of thermal stability in gaseous haloes in which large-amplitude density perturbations are prevalent.

Observations of AGN host galaxies have detected fast molecular outflows, with velocities up to ~1000 km/s and outflow rates up to ~1000 Msol/yr. To explore the origin of these molecular outflows, we ran simulations of an isotropic AGN wind interacting with a uniform ambient ISM. By modelling the time-dependent molecular chemistry in these simulations, we showed that these molecular outflows can arise from the in-situ formation of molecules within the AGN wind. In this talk, I will present the results of radiative transfer modelling of molecular emission lines from these simulations in post-processing. We found that the molecular outflow rates derived from CO emission lines in our simulations at solar metallicity are in agreement with observations. By comparing the CO emission to the actual H2 mass in the simulations, we derive a CO-to-H2 conversion factor of 0.13 Msol/(K km/s pc^2), a factor of 6 lower than the standard ULIRG value that is often assumed in these observations. We also found strong infrared emission lines from warm H2, with excitation temperatures of 400-550 K. The mass of H2 inferred from this warm H2 emission is within a few per cent of the total H2 mass. These warm H2 emission lines are potentially observable by JWST.&nbsp

We study a suite of extremely high-resolution cosmological FIRE simulations of dwarf galaxies ($M_{\rm halo} \lesssim 10^{10}$$M_{\odot}$), run to $z=0$ with $30 M_{\odot}$ resolution, sufficient (for the first time) to resolve the internal structure of individual supernovae remnants within the cooling radius. Every halo with $M_{\rm halo} \gtrsim 10^{8.6} M_{\odot}$ is populated by a resolved {\em stellar} galaxy, suggesting very low-mass dwarfs may be ubiquitous in the field. Our ultra-faint dwarfs (UFDs; $M_{\ast}10^{5} M_{\odot}$) continue forming stars to $z 10^{-4}$ to form a dark matter core $>200$pc, while lower-mass UFDs exhibit cusps down to $\lesssim100$pc, as expected from energetic arguments. Our dwarfs with $M_{\ast}>10^{4}\,M_{\odot}$ have half-mass radii ($R_{\rm 1/2}$) in agreement with Local Group (LG) dwarfs; dynamical mass vs. $R_{1/2}$ and the degree of rotational support also resemble observations. The lowest-mass UFDs are below surface brightness limits of current surveys but are potentially visible in next-generation surveys (e.g. LSST). The stellar metallicities are lower than in LG dwarfs; this may reflect pre-enrichment of the LG by the massive hosts or Pop-III stars. Consistency with lower resolution studies implies that our simulations are numerically robust (for a given physical model)., 14 pages; 9 figures; 1 table; submitted to MNRAS

Observations of AGN host galaxies have detected fast molecular outflows, with velocities up to ~1000 km s-1. However, the origin of these molecular outflows is currently unclear. One possibility is that they are formed from molecular gas that is swept up from the host galaxy by the AGN wind. However, previous studies have suggested that molecular clouds that are swept up by an AGN wind are unlikely to survive being accelerated to such high velocities. An alternative scenario is that molecules may form within the AGN wind material itself. We present a suite of 3D hydrodynamic simulations of an idealised AGN wind that we have run to explore this scenario. These simulations are coupled to a time-dependent chemical model to follow the creation and destruction of molecules, including H2, CO, OH and HCO+. We find that molecules do form within the wind, with molecular outflow rates up to 140 Mʘ yr-1 after 1 Myr. This is sensitive to the ambient ISM density, metallicity, and AGN luminosity. We also compute observable CO emission lines from these simulations using a radiative transfer code in post-processing. The CO-derived outflow rates are comparable to those seen in observations, although the maximum line of sight velocities are a factor ≈2 lower than observed. We find a CO (1-0) to H2 conversion factor of αCO = 0.15 Mʘ (K km s-1 pc2)-1 at solar metallicity, 5 times lower than is typically assumed in observations of such systems.

Observations of AGN host galaxies have detected fast molecular outflows, with velocities up to ~1000 km s-1. However, the origin of these molecular outflows is currently unclear. One possibility is that they are formed from molecular gas that is swept up from the host galaxy by the AGN wind. However, previous studies have suggested that molecular clouds that are swept up by an AGN wind are unlikely to survive being accelerated to such high velocities. An alternative scenario is that molecules may form within the AGN wind material itself. We present a suite of 3D hydrodynamic simulations of an idealised AGN wind that we have run to explore this scenario. These simulations are coupled to a time-dependent chemical model to follow the creation and destruction of molecules, including H2, CO, OH and HCO+. We find that molecules do form within the wind, with molecular outflow rates up to 140 Mʘ yr-1 after 1 Myr. This is sensitive to the ambient ISM density, metallicity, and AGN luminosity. We also compute observable CO emission lines from these simulations using a radiative transfer code in post-processing. The CO-derived outflow rates are comparable to those seen in observations, although the maximum line of sight velocities are a factor ≈2 lower than observed. We find a CO (1-0) to H2 conversion factor of αCO = 0.15 Mʘ (K km s-1 pc2)-1 at solar metallicity, 5 times lower than is typically assumed in observations of such systems.