63 research outputs found
The formation of disc galaxies in high resolution moving-mesh cosmological simulations
We present cosmological hydrodynamical simulations of eight Milky Way-sized
haloes that have been previously studied with dark matter only in the Aquarius
project. For the first time, we employ the moving-mesh code AREPO in zoom
simulations combined with a comprehensive model for galaxy formation physics
designed for large0 cosmological simulations. Our simulations form in most of
the eight haloes strongly disc-dominated systems with realistic rotation
curves, close to exponential surface density profiles, a stellar-mass to
halo-mass ratio that matches expectations from abundance matching techniques,
and galaxy sizes and ages consistent with expectations from large galaxy
surveys in the local Universe. There is no evidence for any dark matter core
formation in our simulations, even so they include repeated baryonic outflows
by supernova-driven winds and black hole quasar feedback. For one of our
haloes, the object studied in the recent `Aquila' code comparison project, we
carried out a resolution study with our techniques, covering a dynamic range of
64 in mass resolution. Without any change in our feedback parameters, the final
galaxy properties are reassuringly similar, in contrast to other modelling
techniques used in the field that are inherently resolution dependent. This
success in producing realistic disc galaxies is reached, in the context of our
interstellar medium treatment, without resorting to a high density threshold
for star formation, a low star formation efficiency, or early stellar feedback,
factors deemed crucial for disc formation by other recent numerical studies.Comment: 28 pages, 23 figures, 2 tables. Accepted for publication in MNRAS.
Added 2 figures and minor text changes to match the accepted versio
The large-scale properties of simulated cosmological magnetic fields
We perform uniformly sampled large-scale cosmological simulations including
magnetic fields with the moving mesh code AREPO. We run two sets of MHD
simulations: one including adiabatic gas physics only; the other featuring the
fiducial feedback model of the Illustris simulation. In the adiabatic case, the
magnetic field amplification follows the scaling derived
from `flux-freezing' arguments, with the seed field strength providing an
overall normalization factor. At high baryon overdensities the amplification is
enhanced by shear flows and turbulence. Feedback physics and the inclusion of
radiative cooling change this picture dramatically. In haloes, gas collapses to
much larger densities and the magnetic field is amplified strongly and to the
same maximum intensity irrespective of the initial seed field of which any
memory is lost. At lower densities a dependence on the seed field strength and
orientation, which in principle can be used to constrain models of cosmic
magnetogenesis, is still present. Inside the most massive haloes magnetic
fields reach values of , in agreement with galaxy
cluster observations. The topology of the field is tangled and gives rise to
rotation measure signals in reasonable agreement with the observations.
However, the rotation measure signal declines too rapidly towards larger radii
as compared to observational data.Comment: 23 pages, 19 figures, 1 table. Accepted for publication in MNRAS.
Edited to match published versio
Thermonuclear explosion of a massive hybrid HeCO white-dwarf triggered by a He-detonation on a companion
Normal type Ia supernovae (SNe) are thought to arise from the thermonuclear
explosion of massive ( M) carbon-oxygen white dwarfs (WDs),
although the exact mechanism is debated. In some models helium accretion onto a
carbon-oxygen (CO) WD from a companion was suggested to dynamically trigger a
detonation of the accreted helium shell. The helium detonation then produces a
shock that after converging on itself close to the core of the CO-WD, triggers
a secondary carbon detonation and gives rise to an energetic explosion.
However, most studies of such scenarios have been done in one or two
dimensions, and/or did not consider self-consistent models for the accretion
and the He-donor. Here we make use of detailed 3D simulation to study the
interaction of a He-rich hybrid HeCO WD with a more
massive CO~WD. We find that accretion from the hybrid
WD onto the CO~WD gives rise to a helium detonation. However, the helium
detonation does not trigger a carbon detonation in the CO~WD. Instead, the
helium detonation burns through the accretion stream to also burn the helium
shell of the donor hybrid HeCO-WD. The detonation of its massive helium shell
then compresses its CO core, and triggers its detonation and full destruction.
The explosion gives rise to a faint, likely highly reddened transient,
potentially observable by the Vera Rubin survey, and the high-velocity () ejection of the heated surviving CO~WD companion.
Pending on uncertainties in stellar evolution we estimate the rate of such
transient to be up to of the rate of type Ia SNe.Comment: 14 pages, 10 figures, accepted by MNRAS, comments welcom
Separate Universe Simulations with IllustrisTNG: baryonic effects on power spectrum responses and higher-order statistics
We measure power spectrum response functions in the presence of baryonic
physical processes using separate universe simulations with the IllustrisTNG
galaxy formation model. The response functions describe how the small-scale
power spectrum reacts to long-wavelength perturbations and they can be
efficiently measured with the separate universe technique by absorbing the
effects of the long modes into a modified cosmology. Specifically, we focus on
the total first-order matter power spectrum response to an isotropic density
fluctuation , which is fully determined by the logarithmic derivative
of the nonlinear matter power spectrum and the
growth-only response function . We find that is not
affected by the baryonic physical processes in the simulations at redshifts and on all scales probed (, i.e. length scales
). In practice, this implies that the power spectrum
fully specifies the baryonic dependence of its response function. Assuming an
idealized lensing survey setup, we evaluate numerically the baryonic impact on
the squeezed-lensing bispectrum and the lensing super-sample power spectrum
covariance, which are given in terms of responses. Our results show that these
higher-order lensing statistics can display varying levels of sensitivity to
baryonic effects compared to the power spectrum, with the squeezed-bispectrum
being the least sensitive. We also show that ignoring baryonic effects on
lensing covariances slightly overestimates the error budget (and is therefore
conservative from the point of view of parameter error bars) and likely has
negligible impact on parameter biases in inference analyses.Comment: 15 pages, 6 figures, 1 table; comments welcomed! v2 matches version
published in MNRA
Hydrodynamical moving-mesh simulations of the tidal disruption of stars by supermassive black holes
When a star approaches a black hole closely, it may be pulled apart by
gravitational forces in a tidal disruption event (TDE). The flares produced by
TDEs are unique tracers of otherwise quiescent supermassive black holes (SMBHs)
located at the centre of most galaxies. In particular, the appearance of such
flares and the subsequent decay of the light curve are both sensitive to
whether the star is partially or totally destroyed by the tidal field. However,
the physics of the disruption and the fall-back of the debris are still poorly
understood. We are here modelling the hydrodynamical evolution of realistic
stars as they approach a SMBH on parabolic orbits, using for the first time the
moving-mesh code AREPO, which is particularly well adapted to the problem
through its combination of quasi-Lagrangian behaviour, low advection errors,
and high accuracy typical of mesh-based techniques. We examine a suite of
simulations with different impact parameters, allowing us to determine the
critical distance at which the star is totally disrupted, the energy
distribution and the fallback rate of the debris, as well as the hydrodynamical
evolution of the stellar remnant in the case of a partial disruption.
Interestingly, we find that the internal evolution of the remnant's core is
strongly influenced by persistent vortices excited in the tidal interaction.
These should be sites of strong magnetic field amplification, and the
associated mixing may profoundly alter the subsequent evolution of the tidally
pruned star.Comment: 13 pages, 9 figures. Accepted for publication by MNRA
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