927 research outputs found
The Zeldovich & Adhesion approximations, and applications to the local universe
The Zeldovich approximation (ZA) predicts the formation of a web of
singularities. While these singularities may only exist in the most formal
interpretation of the ZA, they provide a powerful tool for the analysis of
initial conditions. We present a novel method to find the skeleton of the
resulting cosmic web based on singularities in the primordial deformation
tensor and its higher order derivatives. We show that the A_3-lines predict the
formation of filaments in a two-dimensional model. We continue with
applications of the adhesion model to visualise structures in the local (z <
0.03) universe.Comment: 9 pages, 8 figures, Proceedings of IAU Symposium 308 "The Zeldovich
Universe: Genesis and Growth of the Cosmic Web", 23-28 June 2014, Tallinn,
Estoni
Caustic Skeleton & Cosmic Web
We present a general formalism for identifying the caustic structure of an
evolving mass distribution in an arbitrary dimensional space. For the class of
Hamiltonian fluids the identification corresponds to the classification of
singularities in Lagrangian catastrophe theory. Based on this we develop a
theoretical framework for the formation of the cosmic web, and specifically
those aspects that characterize its unique nature: its complex topological
connectivity and multiscale spinal structure of sheetlike membranes, elongated
filaments and compact cluster nodes. The present work represents an extension
of the work by Arnol'd et al., who classified the caustics for the 1- and
2-dimensional Zel'dovich approximation. His seminal work established the role
of emerging singularities in the formation of nonlinear structures in the
universe. At the transition from the linear to nonlinear structure evolution,
the first complex features emerge at locations where different fluid elements
cross to establish multistream regions. The classification and characterization
of these mass element foldings can be encapsulated in caustic conditions on the
eigenvalue and eigenvector fields of the deformation tensor field. We introduce
an alternative and transparent proof for Lagrangian catastrophe theory, and
derive the caustic conditions for general Lagrangian fluids, with arbitrary
dynamics, including dissipative terms and vorticity. The new proof allows us to
describe the full 3-dimensional complexity of the gravitationally evolving
cosmic matter field. One of our key findings is the significance of the
eigenvector field of the deformation field for outlining the spatial structure
of the caustic skeleton. We consider the caustic conditions for the
3-dimensional Zel'dovich approximation, extending earlier work on those for 1-
and 2-dimensional fluids towards the full spatial richness of the cosmic web
Detecting the orientation of magnetic fields in galaxy clusters
Clusters of galaxies, filled with hot magnetized plasma, are the largest
bound objects in existence and an important touchstone in understanding the
formation of structures in our Universe. In such clusters, thermal conduction
follows field lines, so magnetic fields strongly shape the cluster's thermal
history; that some have not since cooled and collapsed is a mystery. In a
seemingly unrelated puzzle, recent observations of Virgo cluster spiral
galaxies imply ridges of strong, coherent magnetic fields offset from their
centre. Here we demonstrate, using three-dimensional magnetohydrodynamical
simulations, that such ridges are easily explained by galaxies sweeping up
field lines as they orbit inside the cluster. This magnetic drape is then lit
up with cosmic rays from the galaxies' stars, generating coherent polarized
emission at the galaxies' leading edges. This immediately presents a technique
for probing local orientations and characteristic length scales of cluster
magnetic fields. The first application of this technique, mapping the field of
the Virgo cluster, gives a startling result: outside a central region, the
magnetic field is preferentially oriented radially as predicted by the
magnetothermal instability. Our results strongly suggest a mechanism for
maintaining some clusters in a 'non-cooling-core' state.Comment: 48 pages, 21 figures, revised version to match published article in
Nature Physics, high-resolution version available at
http://www.cita.utoronto.ca/~pfrommer/Publications/pfrommer-dursi.pd
Towards Gross-Pitaevskiian Description of Solar System & Galaxies
In this paper, we argue that Gross-Pitaevskii model can be a more complete description of both solar system and spiral galaxies, especially taking into account the nature of chirality and vortices in galaxies. We also hope to bring out some correspondence among existing models, e.g., the topological vortex approach, Burgers equation in the light of KAM theory, and the Cantorian Navier-Stokes approach. We hope further investigation can be done around this line of approach
A diversity of progenitors and histories for isolated spiral galaxies
We analyze a suite of 33 cosmological simulations of the evolution of Milky
Way-mass galaxies in low-density environments. Our sample spans a broad range
of Hubble types at z=0, from nearly bulgeless disks to bulge-dominated
galaxies. Despite the fact that a large fraction of the bulge is typically in
place by z=1, we find no significant correlation between the morphology at z=1
and at z=0. The z=1 progenitors of disk galaxies span a range of morphologies,
including smooth disks, unstable disks, interacting galaxies and
bulge-dominated systems. By z=0.5, spiral arms and bars are largely in place
and the progenitor morphology is correlated with the final morphology. We next
focus on late-type galaxies with a bulge-to-total ratio B/T<0.3 at z=0. These
show a correlation between B/T at z=0 and the mass ratio of the largest merger
at z1. We find that the
galaxies with the lowest B/T tend to have a quiet baryon input history, with no
major mergers at z<2, and with a low and constant gas accretion rate that keeps
a stable angular-momentum direction. More violent merger or gas accretion
histories lead to galaxies with more prominent bulges. Most disk galaxies have
a bulge Sersic index n<2. The galaxies with the highest bulge Sersic index tend
to have histories of intense gas accretion and disk instability rather than
active mergers.Comment: Accepted for publication in ApJ. 29 pages, 32 figure
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