28 research outputs found
Modeling a high velocity LMC. The formation of the Magellanic Stream
I use high resolution N-body/SPH simulations to model the new proper motion
of the Large Magellanic Cloud (LMC) within the Milky Way (MW) halo and
investigate the effects of gravitational and hydrodynamical forces on the
formation of the Magellanic Stream (MS). Both the LMC and the MW are fully self
consistent galaxy models embedded in extended cuspy LCDM dark matter halos. I
find that ram-pressure from a low density ionized halo is sufficient to remove
a large amount of gas from the LMC's disk forming a trailing Stream that
extends more than 120 degrees from the Cloud. Tidal forces elongate the
satellite's disk but do not affect its vertical structure. No stars become
unbound showing that tidal stripping is almost effectiveless.Comment: 6 pages, 3 figures. To be published in proceedings of IAU Symposium
No. 256: The Magellanic System: Stars, Gas, and Galaxies, Jacco Th. van Loon
& Joana M. Oliveira, eds. 2009 (Cambridge: Cambridge University Press
Ram-Pressure Induced Star Formation in the LMC
We use high-resolution n-body/SPH simulations to study the hydrodynamical interaction between the Large Magellanic Cloud and the hot halo of the Milky Way. We investigate whether the ram-pressure acting on the gaseous disk of the satellite can explain the peculiarities observed in the Hi distribution and the location of the recent star formation activit
Effects of ram pressure on the gas distribution and star formation in the Large Magellanic Cloud
We use high-resolution N-body/smoothed particle hydrodynamics (SPH) simulations to study the hydrodynamical interaction between the Large Magellanic Cloud (LMC) and the hot halo of the Milky Way. We investigate whether ram pressure acting on the satellite's interstellar medium can explain the peculiarities observed in the H i distribution and the location of the recent star formation activity. Due to the present nearly edge-on orientation of the disc with respect to the orbital motion, compression at the leading edge can explain the high density region observed in H i at the south-east border. In the case of a face-on disc (according to Mastropietro the LMC was moving almost face-on before the last perigalactic passage), ram pressure directed perpendicular to the disc produces a clumpy structure characterized by voids and high density filaments that resemble those observed by the Parkes H i survey. As a consequence of the very recent edge-on motion, the Hα emission is mainly concentrated on the eastern side where 30 Doradus and most of the supergiant shells are located, although some Hα complexes form a patchy distribution on the entire disc. In this scenario, only the youngest stellar complexes show a progression in age along the leading border of the dis
Simultaneous ram pressure and tidal stripping; how dwarf spheroidals lost their gas
We perform high-resolution N-body+SPH (smoothed particle hydrodynamics) simulations of gas-rich dwarf galaxy satellites orbiting within a Milky Way-sized halo and study for the first time the combined effects of tides and ram pressure. The structure of the galaxy models and the orbital configurations are chosen in accordance with those expected in a Lambda cold dark matter (ΛCDM) universe. While tidal stirring of disky dwarfs produces objects whose stellar structure and kinematics resembles that of dwarf spheroidals after a few orbits, ram pressure stripping is needed to entirely remove their gas component. Gravitational tides can aid ram pressure stripping by diminishing the overall potential of the dwarf, but tides also induce bar formation which funnels gas inwards making subsequent stripping more difficult. This inflow is particularly effective when the gas can cool radiatively. Assuming a low density of the hot Galactic corona consistent with observational constraints, dwarfs with Vpeak 30 km s−1 lose most or all of their gas content only if a heating source keeps the gas extended, partially counteracting the bar-driven inflow. We show that the ionizing radiation from the cosmic ultraviolet (UV) background at z > 2 can provide the required heating. In these objects, most of the gas is removed or becomes ionized at the first pericenter passage, explaining the early truncation of the star formation observed in Draco and Ursa Minor. Galaxies on orbits with larger pericenters and/or falling into the Milky Way halo at lower redshift can retain significant amounts of the centrally concentrated gas. These dwarfs would continue to form stars over a longer period of time, especially close to pericenter passages, as observed in Fornax and other dwarf spheroidal galaxies (dSphs) of the Local Group. The stripped gas breaks up into individual clouds pressure confined by the outer gaseous medium that have masses, sizes and densities comparable to the H-i clouds recently discovered around M3
Morphological evolution of discs in clusters
The recent discovery of hidden non-axisymmetric and disc-like structures in bright Virgo dwarf elliptical and lenticular galaxies (dE/dSph/dS0) indicates that they may have late-type progenitors. Using N-body simulations we follow the evolution of disc galaxies within a A cold dark matter (ACDM) cluster simulated with 107 particles, where the hierarchical growth and galaxy harassment are modelled self-consistently. Most of the galaxies undergo significant morphological transformation, even at the outskirts of the cluster, and move through the Hubble sequence from late-type discs to dwarf spheroidals. None of the discs is completely destroyed, therefore they cannot be the progenitors of ultracompact dwarf (UCD) galaxies. The time evolution of the simulated galaxies is compared with unsharp masked images obtained from Very Large Telescope (VLT) data and the projected kinematics of our models with the latest high-resolution spectroscopic studies from the Keck and Palomar telescopes
Morphological evolution of discs in clusters
The recent discovery of hidden non-axisymmetric and disc-like structures in bright Virgo dwarf elliptical and lenticular galaxies (dE/dSph/dS0) indicates that they may have late-type progenitors. Using N-body simulations we follow the evolution of disc galaxies within a Λ cold dark matter (ΛCDM) cluster simulated with 107 particles, where the hierarchical growth and galaxy harassment are modelled self-consistently. Most of the galaxies undergo significant morphological transformation, even at the outskirts of the cluster, and move through the Hubble sequence from late-type discs to dwarf spheroidals. None of the discs is completely destroyed, therefore they cannot be the progenitors of ultracompact dwarf (UCD) galaxies. The time evolution of the simulated galaxies is compared with unsharp masked images obtained from Very Large Telescope (VLT) data and the projected kinematics of our models with the latest high-resolution spectroscopic studies from the Keck and Palomar telescope
Density Profiles of Cold Dark Matter Substructure: Implications for the Missing Satellites Problem
The structural evolution of substructure in cold dark matter (CDM) models is
investigated combining ``low-resolution'' satellites from cosmological N-body
simulations of parent halos with N=10^7 particles with high-resolution
individual subhalos orbiting within a static host potential. We show that, as a
result of mass loss, convergence in the central density profiles requires the
initial satellites to be resolved with N=10^7 particles and parsec-scale force
resolution. We find that the density profiles of substructure halos can be well
fitted with a power-law central slope that is unmodified by tidal forces even
after the tidal stripping of over 99% of the initial mass and an exponential
cutoff in the outer parts. The solution to the missing-satellites problem
advocated by Stoehr et al. in 2002 relied on the flattening of the dark matter
(DM) halo central density cusps by gravitational tides, enabling the observed
satellites to be embedded within DM halos with maximum circular velocities as
large as 60 km/s. In contrast, our results suggest that tidal interactions do
not provide the mechanism for associating the dwarf spheroidal satellites
(dSphs) of the Milky Way with the most massive substructure halos expected in a
CDM universe. We compare the predicted velocity dispersion profiles of Fornax
and Draco to observations, assuming that they are embedded in CDM halos. Models
with isotropic and tangentially anisotropic velocity distributions for the
stellar component fit the data only if the surrounding DM halos have maximum
circular velocities in the range 20-35 km/s. If the dSphs are embedded within
halos this large then the overabundance of satellites within the concordance
LCDM cosmological model is significantly alleviated, but this still does not
provide the entire solution.Comment: Accepted for publication in ApJ, 17 pages, 9 figures, LaTeX (uses
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Effects of ram pressure on the gas distribution and star formation in the Large Magellanic Cloud
We use high resolution N-body/SPH simulations to study the hydrodynamical
interaction between the Large Magellanic Cloud (LMC) and the hot halo of the
Milky Way. We investigate whether ram-pressure acting on the satellite's ISM
can explain the peculiarities observed in the HI distribution and the location
of the recent star formation activity. Due to the present nearly edge-on
orientation of the disk with respect to the orbital motion, compression at the
leading edge can explain the high density region observed in HI at the
south-east border. In the case of a face-on disk (according to Mastropietro et
al. 2008 the LMC was moving almost face-on before the last perigalactic
passage), ram-pressure directed perpendicularly to the disk produces a clumpy
structure characterized by voids and high density filaments that resemble those
observed by the Parkes HI survey. As a consequence of the very recent edge-on
motion, the H-alpha emission is mainly concentrated on the eastern side where
30 Doradus and most of the supergiant shells are located, although some H-alpha
complexes form a patchy distribution on the entire disk. In this scenario only
the youngest stellar complexes show a progression in age along the leading
border of the disk.Comment: 18 pages, 18 figures, submitted to MNRA
Rehabilitation Modulates High-Order Interactions Among Large-Scale Brain Networks in Subacute Stroke
The recovery of motor functions after stroke is fostered by the functional integration of large-scale brain networks, including the motor network (MN) and high-order cognitive controls networks, such as the default mode (DMN) and executive control (ECN) networks. In this paper, electroencephalography signals are used to investigate interactions among these three resting state networks (RSNs) in subacute stroke patients after motor rehabilitation. A novel metric, the O-information rate (OIR), is used to quantify the balance between redundancy and synergy in the complex high-order interactions among RSNs, as well as its causal decomposition to identify the direction of information flow. The paper also employs conditional spectral Granger causality to assess pairwise directed functional connectivity between RSNs. After rehabilitation, a synergy increase among these RSNs is found, especially driven by MN. From the pairwise description, a reduced directed functional connectivity towards MN is enhanced after treatment. Besides, inter-network connectivity changes are associated with motor recovery, for which the mediation role of ECN seems to play a relevant role, both from pairwise and high-order interactions perspective