180 research outputs found
Powering galactic super-winds with small-scale AGN winds
We present a new implementation for active galactic nucleus (AGN) feedback
through small-scale, ultra-fast winds in the moving-mesh hydrodynamic code
AREPO. The wind is injected by prescribing mass, momentum and energy fluxes
across a spherical boundary centred on a supermassive black hole according to
available constraints for accretion disc winds. After sweeping-up a mass equal
to their own, small-scale winds thermalise, powering energy-driven outflows
with dynamics, structure and cooling properties in excellent agreement with
those of analytic wind solutions. Momentum-driven solutions do not easily
occur, because the Compton cooling radius is usually much smaller than the
free-expansion radius of the small-scale winds. Through various convergence
tests, we demonstrate that our implementation yields wind solutions which are
well converged down to the typical resolution achieved in cosmological
simulations. We test our model in hydrodynamic simulations of isolated Milky
Way - mass galaxies. Above a critical AGN luminosity, initially spherical,
small-scale winds power bipolar, energy-driven super-winds that break out of
the galactic nucleus, flowing at speeds out to
. These energy-driven outflows result in moderate, but
long-term, reduction in star formation, which becomes more pronounced for
higher AGN luminosities and faster small-scale winds. Suppression of star
formation proceeds through a rapid mode that involves the removal of the
highest-density, nuclear gas and through a slower mode that effectively halts
halo gas accretion. Our new implementation makes it possible to model
AGN-driven winds in a physically meaningful and validated way in simulations of
galaxy evolution, the interstellar medium and black hole accretion flows.Comment: 30 pages, 17 figures, MNRAS (Accepted
A finite volume method for two-moment cosmic-ray hydrodynamics on a moving mesh
We present a new numerical algorithm to solve the recently derived equations
of two-moment cosmic ray hydrodynamics (CRHD). The algorithm is implemented as
a module in the moving mesh Arepo code. Therein, the anisotropic transport of
cosmic rays (CRs) along magnetic field lines is discretised using a
path-conservative finite volume method on the unstructured time-dependent
Voronoi mesh of Arepo. The interaction of CRs and gyroresonant Alfv\'en waves
is described by short-timescale source terms in the CRHD equations. We employ a
custom-made semi-implicit adaptive time stepping source term integrator to
accurately integrate this interaction on the small light-crossing time of the
anisotropic transport step. Both the transport and the source term integration
step are separated from the evolution of the magneto-hydrodynamical equations
using an operator split approach. The new algorithm is tested with a variety of
test problems, including shock tubes, a perpendicular magnetised discontinuity,
the hydrodynamic response to a CR overpressure, CR acceleration of a warm
cloud, and a CR blast wave, which demonstrate that the coupling between CR and
magneto-hydrodynamics is robust and accurate. We demonstrate the numerical
convergence of the presented scheme using new linear and non-linear analytic
solutions.Comment: 24 pages, 15 figures, submitted to MNRAS, comments are welcome
Non-ideal magnetohydrodynamics on a moving mesh
In certain astrophysical systems the commonly employed ideal
magnetohydrodynamics (MHD) approximation breaks down. Here, we introduce novel
explicit and implicit numerical schemes of ohmic resistivity terms in the
moving-mesh code AREPO. We include these non-ideal terms for two MHD
techniques: the Powell 8-wave formalism and a constrained transport scheme,
which evolves the cell-centred magnetic vector potential. We test our
implementation against problems of increasing complexity, such as one- and
two-dimensional diffusion problems, and the evolution of progressive and
stationary Alfv\'en waves. On these test problems, our implementation recovers
the analytic solutions to second-order accuracy. As first applications, we
investigate the tearing instability in magnetized plasmas and the gravitational
collapse of a rotating magnetized gas cloud. In both systems, resistivity plays
a key role. In the former case, it allows for the development of the tearing
instability through reconnection of the magnetic field lines. In the latter,
the adopted (constant) value of ohmic resistivity has an impact on both the gas
distribution around the emerging protostar and the mass loading of magnetically
driven outflows. Our new non-ideal MHD implementation opens up the possibility
to study magneto-hydrodynamical systems on a moving mesh beyond the ideal MHD
approximation.Comment: 18 pages, 11 figures, accepted for publication in MNRAS. Revisions to
match the accepted versio
AREPO-RT: Radiation hydrodynamics on a moving mesh
We introduce AREPO-RT, a novel radiation hydrodynamic (RHD) solver for the
unstructured moving-mesh code AREPO. Our method solves the moment-based
radiative transfer equations using the M1 closure relation. We achieve second
order convergence by using a slope limited linear spatial extrapolation and a
first order time prediction step to obtain the values of the primitive
variables on both sides of the cell interface. A Harten-Lax-Van Leer flux
function, suitably modified for moving meshes, is then used to solve the
Riemann problem at the interface. The implementation is fully conservative and
compatible with the individual timestepping scheme of AREPO. It incorporates
atomic Hydrogen (H) and Helium (He) thermochemistry, which is used to couple
the ultra-violet (UV) radiation field to the gas. Additionally, infrared
radiation is coupled to the gas under the assumption of local thermodynamic
equilibrium between the gas and the dust. We successfully apply our code to a
large number of test problems, including applications such as the expansion of
regions, radiation pressure driven outflows and the levitation
of optically thick layer of gas by trapped IR radiation. The new implementation
is suitable for studying various important astrophysical phenomena, such as the
effect of radiative feedback in driving galactic scale outflows, radiation
driven dusty winds in high redshift quasars, or simulating the reionisation
history of the Universe in a self consistent manner.Comment: v2, accepted for publication in MNRAS, changed to a Strang split
scheme to achieve second order convergenc
LYRA I: Simulating the multi-phase ISM of a dwarf galaxy with variable energy supernovae from individual stars
We introduce the LYRA project, a new high resolution galaxy formation model
built within the framework of the cosmological hydro-dynamical moving mesh code
AREPO. The model resolves the multi-phase interstellar medium down to 10 K. It
forms individual stars sampled from the initial mass function (IMF), and tracks
their lifetimes and death pathways individually. Single supernova (SN) blast
waves with variable energy are followed within the hydrodynamic calculation to
interact with the surrounding interstellar medium (ISM). In this paper, we
present the methods and apply the model to a isolated halo.
We demonstrate that the majority of supernovae are Sedov-resolved at our
fiducial gas mass resolution of . We show that our SN feedback
prescription self-consistently produces a hot phase within the ISM that drives
significant outflows, reduces the gas density and suppresses star formation.
Clustered SN play a major role in enhancing the effectiveness of feedback,
because the majority of explosions occur in low density material. Accounting
for variable SN energy allows the feedback to respond directly to stellar
evolution. We show that the ISM is sensitive to the spatially distributed
energy deposition. It strongly affects the outflow behaviour, reducing the mass
loading by a factor of 2-3, thus allowing the galaxy to retain a higher
fraction of mass and metals. LYRA makes it possible to use a comprehensive
multi-physics ISM model directly in cosmological (zoom) simulations of dwarf
and higher mass galaxies.Comment: 20 pages, 19 figures, published in MNRA
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