•Formation of Saturn’s rings and Mimas from the collision of a comet with an icy moon.•Saturn ring formation mechanism produces nearly pure ice rings recently.•Ring parent moon initially trapped in ...mean motion resonance heats Enceladus.
The disruption of an icy moon in a collision with an interloping comet a few hundred million years ago is a simple way to create Saturn’s rings. A ring parent moon with a mass comparable to Mimas could be trapped in mean motion resonance with Enceladus and Dione in an orbit near the current outer edge of the rings just beyond the Roche zone. I present collisional N-body simulations of cometary impacts that lead to the partial disruption of a differentiated moon with a rocky core and icy mantle. The core can survive largely intact while the debris from the mantle settles into a ring of predominantly ice particles straddling the orbital radius of the parent moon. The nascent ring spreads radially due to collisional viscosity while mass re-accretes onto the remnant rocky core to form a new moon that can be identified as Mimas. The icy debris that migrates into the Roche zone evolves into Saturn’s ring system. Torques from tidal interaction with Saturn and resonant interactions with the rings push the recently formed Mimas outward to its current position on the same timescale of a few hundred million years. This scenario accounts for the high ice fraction observed in Saturn’s rings and explains why the ring mass is comparable to the mass of Mimas. The prior existence of a ring parent moon in mean motion resonance results in a tidal heating rate for Enceladus in the recent past that is significantly larger than the current rate.
The dark matter halos in Delta *L cold dark matter cosmological simulations are triaxial and highly flattened. In many cases, these triaxial equilibria are also tumbling slowly, typically about their ...short axes, with periods of order a Hubble time. Halos may therefore exert a slowly changing external torque on spiral galaxies that can affect their dynamical evolution in interesting ways. We examine the effect of the external torques exerted by a tumbling quadrupolar tidal field on the evolution of spiral galaxies using N-body simulations with realistic, disk galaxy models. We measure the amplitude of the external quadrupole moments of dark halos in cosmological simulations and use these to force disk galaxy models in a series of N-body experiments for a range of pattern speeds. We find that the torques are strong enough to induce long-lived transient warps in disks similar to those observed in real spirals and also induce the bar instability at later times in some galaxy models that are otherwise stable for long periods of time in isolation. We also observe forced spiral structure near the edge of the disk where normally self gravity is too weak to be responsible for such a structure. This overlooked influence of dark halos may well be responsible for many of the peculiar aspects of disk galaxy dynamics.
In hierarchical cosmological models, galaxies grow in mass through the continual accretion of smaller ones. The tidal disruption of these systems is expected to result in loosely bound stars ...surrounding the galaxy, at distances that reach 10–100 times the radius of the central disk. The number, luminosity and morphology of the relics of this process provide significant clues to galaxy formation history, but obtaining a comprehensive survey of these components is difficult because of their intrinsic faintness and vast extent. Here we report a panoramic survey of the Andromeda galaxy (M31). We detect stars and coherent structures that are almost certainly remnants of dwarf galaxies destroyed by the tidal field of M31. An improved census of their surviving counterparts implies that three-quarters of M31’s satellites brighter than Mv = -6 await discovery. The brightest companion, Triangulum (M33), is surrounded by a stellar structure that provides persuasive evidence for a recent encounter with M31. This panorama of galaxy structure directly confirms the basic tenets of the hierarchical galaxy formation model and reveals the shared history of M31 and M33 in the unceasing build-up of galaxies.
ABSTRACT Observations consistently show that elliptical galaxies follow a tight "fundamental plane" (FP) scaling relation between size, mean surface brightness, and velocity dispersion, with the form .... This relation not only has very small (<0.05 dex) intrinsic scatter, but also has significantly different coefficients from the expected virial scaling (a "tilt"). We analyze hundreds of simulations of elliptical galaxies formed from mergers of spiral galaxies in groups to determine if the FP can emerge from multiple, mostly minor and hierarchical collisionless mergers. We find that these simulated ellipticals lie on a similar FP with and . The scatter about this plane is not larger than observed, while the tilt is in the correct sense, although a is larger than for typical observations. This supports the idea that collisionless mergers can contribute significantly to the tilt of the FP. The tilt is mainly driven by a mass-dependent dark matter fraction, such that more massive galaxies have larger dark matter fractions within Re. We further discuss the origin of this mass-dependent dark matter fraction and its compatibility with strong lensing observations, as well as the links between the FP, dynamical masses, and the virial theorem.
We report the search for intracluster light in four Abell type II-III (non- cD) galaxy clusters: A801, A1234, A1553, and A1914. We find that on average these clusters contain approx10% of their ...detected stellar luminosity in a diffuse component. We show that for two of the clusters the intracluster light closely follows the galaxy distribution, but in the other two cases, there are noticeable differences between the spatial distribution of the galaxies and the intracluster light. We report the results of a search for intracluster tidal debris in each cluster and note that A1914 in particular has a number of strong tidal features likely due to its status as a recent cluster merger. One of the A1914 features appears to be spatially coincident with an extension seen in weak lensing maps, implying that the feature traces a large amount of mass. We compare these results with numerical simulations of hierarchically formed galaxy clusters and find good general agreement between the observed and simulated images, although we also find that our observations sample only the brightest features of the intracluster light. Together, these results suggest that intracluster light can be a valuable tool in determining the evolutionary state of galaxy clusters.
Dynamical Blueprints for Galaxies Widrow, Lawrence M; Pym, Brent; Dubinski, John
The Astrophysical journal,
06/2008, Letnik:
679, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We present an axisymmetric, equilibrium model for late-type galaxies which consists of an exponential disk, a Sersic bulge, and a cuspy dark halo. The model is specified by a phase-space distribution ...function which, in turn, depends on the integrals of motion. Bayesian statistics and the Markov chain Monte Carlo method are used to tailor the model to satisfy observational data and theoretical constraints. By way of example, we construct a chain of 10 super(5) models for the Milky Way designed to fit a wide range of photometric and kinematic observations. From this chain, we calculate the probability distribution function of important Galactic parameters such as the Sersic index of the bulge, the disk scale length, and the disk, bulge, and halo masses. We also calculate the probability distribution function of the local dark matter velocity dispersion and density, two quantities of paramount significance for terrestrial dark matter detection experiments. Although the Milky Way models in our chain all satisfy the prescribed observational constraints, they vary considerably in key structural parameters and therefore respond differently to nonaxisymmetric perturbations. We simulate the evolution of 25 models which have different Toomre Q and Goldreich- Tremaine X parameters. Virtually all of these models form a bar, although some more quickly than others. The bar pattern speeds are image40-50 km s super(-1) kpc super(-1) at the time when they form and then decrease, presumably due to coupling of the bar with the halo. Since the Galactic bar has a pattern speed image50 km s super(-1) kpc super(-1), we conclude that it must have formed recently.
Weak gravitational lensing provides a direct statistical measure of dark matter distribution. The variance is easiest to measure, which constrains the degenerate product σ8Ω0.60. The degeneracy is ...broken by measuring the skewness arising from the fact that densities must remain positive, which is not possible when the initially symmetric perturbations become nonlinear. Skewness measures the nonlinear mass scale, which in combination with the variance measures Ω0 directly. We present the first detection of dark matter skewness from the VIRMOS-DESCART survey. We have measured the full three-point function and its projections onto windowed skewness. We separate the lensing mode and the B-mode. The lensing skewness is detected for a compensated Gaussian on scales of 5.37‧ to be κ3=(1.06+/-0.06)×10-6. The B-modes are consistent with zero at this scale. The variance for the same window function is κ2=(5.32+/-0.62+/-0.98)×10-5, resulting in S3=375+342-124. Comparing with N-body simulations, we find Ω0<0.5 at 90% confidence. The Canada-France-Hawaii Telescope legacy survey and newer simulations should be able to improve significantly on the constraint.
PDF
