20 research outputs found
Cold Dark Matter Substructures in Early-Type Galaxy Halos
We present initial results from the "Ponos" zoom-in numerical simulations of
dark matter substructures in massive ellipticals. Two very highly resolved dark
matter halos with and and different ("violent" vs. "quiescent")
assembly histories have been simulated down to in a CDM
cosmology with a total of 921,651,914 and 408,377,544 particles, respectively.
Within the virial radius, the total mass fraction in self-bound subhalos at the present epoch is 15% for the violent
host and 16.5% for the quiescent one. At , these fractions increase to
19 and 33%, respectively, as more recently accreted satellites are less prone
to tidal destruction. In projection, the average fraction of surface mass
density in substructure at a distance of ( kpc)
from the two halo centers ranges from 0.6% to %, significantly
higher than measured in simulations of Milky Way-sized halos. The contribution
of subhalos with to the projected mass
fraction is between one fifth and one third of the total, with the smallest
share found in the quiescent host. We assess the impact of baryonic effects via
twin, lower-resolution hydrodynamical simulations that include
metallicity-dependent gas cooling, star formation, and a
delayed-radiative-cooling scheme for supernova feedback. Baryonic contraction
produces a super-isothermal total density profile and increases the number of
massive subhalos in the inner regions of the main host. The host density
profiles and projected subhalo mass fractions appear to be broadly consistent
with observations of gravitational lenses.Comment: 14 pages, 15 figures, accepted for publication in ApJ after minor
revisions, note the new Fig.
The Argo Simulation: II. The Early Build-up of the Hubble Sequence
The Hubble sequence is a common classification scheme for the structure of
galaxies. Despite the tremendous usefulness of this diagnostic, we still do not
fully understand when, where, and how this morphological ordering was put in
place. Here, we investigate the morphological evolution of a sample of 22 high
redshift () galaxies extracted from the Argo simulation. Argo is a
cosmological zoom-in simulation of a group-sized halo and its environment. It
adopts the same high resolution ( M, pc) and
sub-grid physical model that was used in the Eris simulation but probes a
sub-volume almost ten times bigger with as many as 45 million gas and star
particles in the zoom-in region. Argo follows the early assembly of galaxies
with a broad range of stellar masses (
at ), while resolving properly their structural properties. We
recover a diversity of morphologies, including late-type/irregular disc
galaxies with flat rotation curves, spheroid dominated early-type discs, and a
massive elliptical galaxy, already established at . We identify major
mergers as the main trigger for the formation of bulges and the steepening of
the circular velocity curves. Minor mergers and non-axisymmetric perturbations
(stellar bars) drive the bulge growth in some cases. The specific angular
momenta of the simulated disc components fairly match the values inferred from
nearby galaxies of similar once the expected redshift evolution of
disc sizes is accounted for. We conclude that morphological transformations of
high redshift galaxies of intermediate mass are likely triggered by processes
similar to those at low redshift and result in an early build-up of the Hubble
sequence.Comment: 17 pages, 13 figures, accepted for publication in MNRA
Dynamics and spin alignment in massive, gravito-turbulent circumbinary discs around supermassive black hole binaries
Parsec-scale separation supermassive black hole binaries in the centre of
gas-rich galaxy merger remnants could be surrounded by massive circumbinary
discs (CBDs). Black hole mass and spin evolution during the gas-rich binary
inspiral are crucial in determining the direction and power of relativistic
jets that radio observations with LOFAR and SKAO will probe, and for predicting
gravitational wave (GW) emission that IPTA and LISA will measure. We present 3D
hydrodynamic simulations capturing gas-rich, self-gravitating CBDs around a
M supermassive black hole binary, that probe different
mass ratios, eccentricities and inclinations. We employ a sub-grid
Shakura-Sunyaev accretion disc to self-consistently model black hole mass and
spin evolution together with super-Lagrangian refinement techniques to resolve
gas flows, streams and mini-discs within the cavity, which play a fundamental
role in torquing and feeding the binary. We find that higher mass ratio and
eccentric binaries result in larger cavities, while retrograde binaries result
in smaller cavities. All of the simulated binaries are expected to shrink with
net gravitational torques being negative. Unlike previous simulations, we do
not find preferential accretion onto the secondary black hole. This implies
smaller chirp masses at coalescence and hence a weaker GW background.
Critically this means that spin-alignment is faster than the binary inspiral
timescale even for low mass ratios. However, we find that mini-disc and hence
spin alignment is not guaranteed in initially misaligned systems, potentially
leading to a significant fraction of recoiled remnants displaced from their
host galaxies if chaotic accretion is the dominant feeding channel.Comment: 27 pages, 14 figures, submitted to MNRAS. Comments and feedback
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Orbital decay of supermassive black hole binaries in clumpy multiphase merger remnants
We simulate an equal-mass merger of two Milky Way-size galaxy discs with moderate gas fractions at parsec-scale resolution including a new model for radiative cooling and heating in a multiphase medium, as well as star formation and feedback from supernovae. The two discs initially have a 2.6×106 M⊙ supermassive black hole (SMBH) embedded in their centres. As the merger completes and the two galactic cores merge, the SMBHs form a pair with a separation of a few hundred pc that gradually decays. Due to the stochastic nature of the system immediately following the merger, the orbital plane of the binary is significantly perturbed. Furthermore, owing to the strong starburst the gas from the central region is completely evacuated, requiring ∼10Myr for a nuclear disc to rebuild. Most importantly, the clumpy nature of the interstellar medium has a major impact on the dynamical evolution of the SMBH pair, which undergo gravitational encounters with massive gas clouds and stochastic torquing by both clouds and spiral modes in the disc. These effects combine to greatly delay the decay of the two SMBHs to separations of a few parsecs by nearly two orders of magnitude, ∼108yr, compared to previous work. In mergers of more gas-rich, clumpier galaxies at high redshift stochastic torques will be even more pronounced and potentially lead to stronger modulation of the orbital decay. This suggests that SMBH pairs at separations of several tens of parsecs should be relatively common at any redshif
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