Gas blown away from galactic disks by supernova (SN) feedback plays a key role in galaxy evolution. We investigate outflows utilizing the solar neighborhood model of our high-resolution, local ...galactic disk simulation suite, TIGRESS. In our numerical implementation, star formation and SN feedback are self-consistently treated and well resolved in the multiphase, turbulent, magnetized interstellar medium. Bursts of star formation produce spatially and temporally correlated SNe that drive strong outflows, consisting of hot ( ) winds and warm ( ) fountains. The hot gas at distance from the midplane has mass and energy fluxes nearly constant with d. The hot flow escapes our local Cartesian box barely affected by gravity, and is expected to accelerate up to terminal velocity of . The mean mass and energy loading factors of the hot wind are 0.1 and 0.02, respectively. For warm gas, the mean outward mass flux through is comparable to the mean star formation rate, but only a small fraction of this gas is at velocity . Thus, the warm outflows eventually fall back as inflows. The warm fountain flows are created by expanding hot superbubbles at at larger d neither ram pressure acceleration nor cooling transfers significant momentum or energy flux from the hot wind to the warm outflow. The velocity distribution at launching near is a better representation of warm outflows than a single mass loading factor, potentially enabling development of subgrid models for warm galactic winds in arbitrary large-scale galactic potentials.
We introduce TIGRESS, a novel framework for multi-physics numerical simulations of the star-forming interstellar medium (ISM) implemented in the Athena MHD code. The algorithms of TIGRESS are ...designed to spatially and temporally resolve key physical features, including: (1) the gravitational collapse and ongoing accretion of gas that leads to star formation in clusters; (2) the explosions of supernovae (SNe), both near their progenitor birth sites and from runaway OB stars, with time delays relative to star formation determined by population synthesis; (3) explicit evolution of SN remnants prior to the onset of cooling, which leads to the creation of the hot ISM; (4) photoelectric heating of the warm and cold phases of the ISM that tracks the time-dependent ambient FUV field from the young cluster population; (5) large-scale galactic differential rotation, which leads to epicyclic motion and shears out overdense structures, limiting large-scale gravitational collapse; (6) accurate evolution of magnetic fields, which can be important for vertical support of the ISM disk as well as angular momentum transport. We present tests of the newly implemented physics modules, and demonstrate application of TIGRESS in a fiducial model representing the solar neighborhood environment. We use a resolution study to demonstrate convergence and evaluate the minimum resolution Δ x required to correctly recover several ISM properties, including the star formation rate, wind mass-loss rate, disk scale height, turbulent and Alfvénic velocity dispersions, and volume fractions of warm and hot phases. For the solar neighborhood model, all these ISM properties are converged at Δ x ≤ 8 pc .
Abstract
Winds from massive stars have velocities of 1000 km s
−1
or more and produce hot, high-pressure gas when they shock. We develop a theory for the evolution of bubbles driven by the collective ...winds from star clusters early in their lifetimes, which involves interaction with the turbulent, dense interstellar medium of the surrounding natal molecular cloud. A key feature is the fractal nature of the hot bubble’s surface. The large area of this interface with surrounding denser gas strongly enhances energy losses from the hot interior, enabled by turbulent mixing and subsequent cooling at temperatures
T
∼ 10
4
–10
5
K, where radiation is maximally efficient. Due to the extreme cooling, the bubble radius scales differently (
) from the classical Weaver et al. solution and has expansion velocity and momentum lower by factors of 10–10
2
at given
, with pressure lower by factors of 10
2
–10
3
. Our theory explains the weak X-ray emission and low shell expansion velocities of observed sources. We discuss further implications of our theory for observations of the hot bubbles and cooled expanding shells created by stellar winds and for predictions of feedback-regulated star formation in a range of environments. In a companion paper, we validate our theory with a suite of hydrodynamic simulations.
ABSTRACT We use numerical simulations to analyze the evolution and properties of superbubbles (SBs), driven by multiple supernovae (SNe), that propagate into the two-phase (warm/cold), cloudy ...interstellar medium (ISM). We consider a range of mean background densities and intervals between SNe , and follow each SB until the radius reaches , where H is the characteristic ISM disk thickness. Except for embedded dense clouds, each SB is hot until a time when the shocked warm gas at the outer front cools and forms an overdense shell. Subsequently, diffuse gas in the SB interior remains at , with an expansion velocity (both highest for low ). At late times, the warm shell gas velocities are several tens to . While shell velocities are too low to escape from a massive galaxy, they are high enough to remove substantial mass from dwarfs. Dense clouds are also accelerated, reaching a few to tens of . We measure the mass in hot gas per SN, , and the total radial momentum of the bubble per SN, . After , (highest for low ), while (highest for high ). If galactic winds in massive galaxies are loaded by the hot gas in SBs, we conclude that the mass-loss rates would generally be lower than star formation rates. Only if the SN cadence is much higher than usual in galactic disks, as may occur for nuclear starbursts, can SBs breakout while hot and expel up to 10 times the mass locked up in stars. The momentum injection values, , are consistent with requirements to control star formation rates within galaxies at observed levels.
Abstract
The star formation rate (SFR) in galactic disks depends on both the quantity of the available interstellar medium (ISM) gas and its physical state. Conversely, the ISM’s physical state ...depends on the SFR, because the “feedback” energy and momentum injected by recently formed massive stars is crucial to offsetting losses from turbulent dissipation and radiative cooling. The ISM’s physical state also responds to the gravitational field that confines it, with increased weight driving higher pressure. In a quasi-steady state, it is expected that the mean total pressure of different thermal phases will match each other, that the component pressures and total pressure will satisfy thermal and dynamical equilibrium requirements, and that the SFR will adjust as needed to provide the requisite stellar radiation and supernova feedback. The pressure-regulated, feedback-modulated (PRFM) theory of the star-forming ISM formalizes these ideas, leading to a prediction that the SFR per unit area, Σ
SFR
, will scale nearly linearly with ISM weight
. In terms of the large-scale gas surface density Σ
gas
, stellar plus dark matter density
ρ
sd
, and effective ISM velocity dispersion
σ
eff
, an observable weight estimator is
≈
P
DE
=
π
G
Σ
gas
2
/
2
+
Σ
gas
(
2
G
ρ
sd
)
1
/
2
σ
eff
, and this is predicted to match the total midplane pressure
P
tot
. Using a suite of multiphase magnetohydrodynamic simulations run with the TIGRESS computational framework, we test the principles of the PRFM model and calibrate the total feedback yield ϒ
tot
=
P
tot
/Σ
SFR
∼ 1000 km s
−1
, as well as its components. We compare the results from TIGRESS to theory, previous numerical simulations, and observations, finding excellent agreement.
We present the first large set of all-sky synthetic dust polarization maps derived directly from a self-consistent magnetohydrodynamics simulation using the TIGRESS framework. Turbulence in this ...simulation is predominantly driven by supernova explosions, with rates that are self-consistently regulated by feedback loops. The simulation covers both the outer scale and inertial range of turbulence with uniformly high resolution. The shearing-box utilized in the simulation, in concert with resolved supernova-driven turbulence, enables the capturing of generation, growth, and saturation of both turbulent and mean magnetic fields. We construct polarization maps at 353 GHz, as seen by observers inside a model of the multiphase, turbulent, magnetized interstellar medium (ISM). To fully sample the simulated ISM state, we use 350 snapshots spanning over (more than six feedback loops) and nine representative observers. The synthetic skies show a prevalent E/B power asymmetry ( ) and positive TE correlation in broad agreement with observations by the Planck satellite. However, the ranges of and are generally lower than those measured by Planck. We find large fluctuations of E/B asymmetry and TE correlation depending on the observer's position and temporal fluctuations of ISM properties due to bursts of star formation. The synthetic maps are made publicly available to provide novel models of the microwave sky.
Abstract
In a companion paper, we develop a theory for the evolution of stellar wind-driven bubbles in dense, turbulent clouds. This theory proposes that turbulent mixing at a fractal bubble/shell ...interface leads to highly efficient cooling, in which the vast majority of the input wind energy is radiated away. This energy loss renders the majority of the bubble evolution momentum driven rather than energy driven, with expansion velocities and pressures orders of magnitude lower than in the classical Weaver et al. solution. In this paper, we validate our theory with three-dimensional, hydrodynamic simulations. We show that extreme cooling is not only possible, but is generic to star formation in turbulent clouds over more than three orders of magnitude in density. We quantify the few free parameters in our theory, and show that the momentum exceeds the wind input rate by only a factor
. We verify that the bubble/cloud interface is a fractal with dimension
. The measured turbulent amplitude (
) in the hot gas near the interface is shown to be consistent with theoretical requirements for turbulent diffusion to efficiently mix and radiate away most of the wind energy. The fraction of energy remaining after cooling is only
, decreasing with time, explaining observations that indicate low hot-gas content and weak dynamical effects of stellar winds.
Large-scale outflows in star-forming galaxies are observed to be ubiquitous and are a key aspect of theoretical modeling of galactic evolution, the focus of the Simulating Multiscale Astrophysics to ...Understand Galaxies (SMAUG) project. Gas blown out from galactic disks, similar to gas within galaxies, consists of multiple phases with large contrasts of density, temperature, and other properties. To study multiphase outflows as emergent phenomena, we run a suite of rougly parsec-resolution local galactic disk simulations using the TIGRESS framework. Explicit modeling of the interstellar medium (ISM), including star formation and self-consistent radiative heating plus supernova feedback, regulates ISM properties and drives the outflow. We investigate the scaling of outflow mass, momentum, energy, and metal loading factors with galactic disk properties, including star formation rate (SFR) surface density ( SFR ∼ 10−4 − 1 M kpc−2 yr−1), gas surface density ( ), and total midplane pressure (or weight; ). The main components of outflowing gas are mass-delivering cool gas (T ∼ 104 K) and energy/metal-delivering hot gas (T 106 K). Cool mass outflow rates measured at outflow launch points (one or two scale heights ) are 1-100 times the SFR (decreasing with SFR), although in massive galaxies most mass falls back owing to insufficient outflow velocity. The hot galactic outflow carries mass comparable to 10% of the SFR, together with 10%-20% of the energy and 30%-60% of the metal mass injected by SN feedback. Importantly, our analysis demonstrates that in any physically motivated cosmological wind model it is crucial to include at least two distinct thermal wind components.
Abstract
Recent measurements of Galactic polarized dust emission have found a nonzero
TB
signal, a correlation between the total intensity and the
B
-mode polarization component. We present evidence ...that this parity-odd signal is driven by the relative geometry of the magnetic field and the filamentary interstellar medium in projection. Using neutral hydrogen morphology and Planck polarization data, we find that the angle between intensity structures and the plane-of-sky magnetic field orientation is predictive of the signs of Galactic
TB
and
EB
. Our results suggest that magnetically misaligned filamentary dust structures introduce nonzero
TB
and
EB
correlations in the dust polarization, and that the intrinsic dust
EB
can be predicted from measurements of dust
TB
and
TE
over the same sky mask. We predict correlations between
TE
,
TB
,
EB
, and
EE
/
BB
, and confirm our predictions using synthetic dust polarization maps from magnetohydrodynamic simulations. We introduce and measure a scale-dependent effective magnetic misalignment angle,
ψ
ℓ
dust
∼
5
°
for 100 ≲
ℓ
≲ 500, and predict a positive intrinsic dust
EB
with amplitude
D
ℓ
EB
≲
2.5
μ
K
CMB
2
for the same multipole range at 353 GHz over our sky mask. Both the sign and amplitude of the Galactic
EB
signal can change with the sky area considered. Our results imply that searches for parity violation in the cosmic microwave background must account for the nonzero Galactic
EB
and
TB
signals, necessitating revision of existing analyses of the evidence for cosmic birefringence.
ABSTRACT Supernova (SN) explosions deposit prodigious energy and momentum in their environments, with the former regulating multiphase thermal structure and the latter regulating turbulence and star ...formation rates in the interstellar medium (ISM). However, systematic studies quantifying the impact of SNe in realistic inhomogeneous ISM conditions have been lacking. Using three-dimensional hydrodynamic simulations, we investigate the dependence of radial momentum injection on both physical conditions (considering a range of mean density n0 = 0.1- ) and numerical parameters. Our inhomogeneous simulations adopt two-phase background states that result from thermal instability in atomic gas. Although the supernova remnant (SNR) morphology becomes highly complex for inhomogeneous backgrounds, the radial momentum injection is remarkably insensitive to environmental details. For our two-phase simulations, the final momentum produced by a single SN is given by . This is only 5% less than the momentum injection for a homogeneous environment with the same mean density, and only 30% greater than the momentum at the time of shell formation. The maximum mass in hot gas is also quite insensitive to environmental inhomogeneity. Strong magnetic fields alter the hot gas mass at very late times, but the momentum injection remains the same. Initial experiments with multiple spatially correlated SNe show a momentum per event nearly as large as single-SN cases. We also present a full numerical parameter study to assess convergence requirements. For convergence in the momentum and other quantities, we find that the numerical resolution Δ and the initial size of the SNR must satisfy , where the shell formation radius is given by for two-phase models (or 30% smaller for a homogeneous medium).
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