2,986 research outputs found
A re-interpretation of the Triangulum-Andromeda stellar clouds: a population of halo stars kicked out of the Galactic disk
The Triangulum-Andromeda stellar clouds (TriAnd1 and TriAnd2) are a pair of
concentric ring- or shell-like over-densities at large ( 30 kpc)
and ( -10 kpc) in the Galactic halo that are thought to have been
formed from the accretion and disruption of a satellite galaxy. This paper
critically re-examines this formation scenario by comparing the number ratio of
RR Lyrae to M giant stars associated with the TriAnd clouds with other
structures in the Galaxy. The current data suggest a stellar population for
these over-densities ( at 95% confidence) quite unlike
any of the known satellites of the Milky Way ( for
the very largest and for the smaller satellites) and more
like the population of stars born in the much deeper potential well inhabited
by the Galactic disk (). N-body simulations of a
Milky-Way-like galaxy perturbed by the impact of a dwarf galaxy demonstrate
that, in the right circumstances, concentric rings propagating outwards from
that Galactic disk can plausibly produce similar over-densities. These results
provide dramatic support for the recent proposal by Xu et al. (2015) that,
rather than stars accreted from other galaxies, the TriAnd clouds could
represent stars kicked-out from our own disk. If so, these would be the first
populations of disk stars to be found in the Galactic halo and a clear
signature of the importance of this second formation mechanism for stellar
halos more generally. Moreover, their existence at the very extremities of the
disk places strong constraints on the nature of the interaction that formed
them.Comment: 27 pages, 8 figures; published in MNRA
Disk Heating, Galactoseismology, and the Formation of Stellar Halos
Deep photometric surveys of the Milky Way have revealed diffuse structures
encircling our Galaxy far beyond the "classical" limits of the stellar disk.
This paper reviews results from our own and other observational programs, which
together suggest that, despite their extreme positions, the stars in these
structures were formed in our Galactic disk. Mounting evidence from recent
observations and simulations implies kinematic connections between several of
these distinct structures. This suggests the existence of collective disk
oscillations that can plausibly be traced all the way to asymmetries seen in
the stellar velocity distribution around the Sun. There are multiple
interesting implications of these findings: they promise new perspectives on
the process of disk heating, they provide direct evidence for a stellar halo
formation mechanism in addition to the accretion and disruption of satellite
galaxies, and, they motivate searches of current and near-future surveys to
trace these oscillations across the Galaxy. Such maps could be used as
dynamical diagnostics in the emerging field of "Galactoseismology", which
promises to model the history of interactions between the Milky Way and its
entourage of satellites, as well examine the density of our dark matter halo.
As sensitivity to very low surface brightness features around external galaxies
increases, many more examples of such disk oscillations will likely be
identified. Statistical samples of such features not only encode detailed
information about interaction rates and mergers, but also about long
sought-after dark matter halo densities and shapes. Models for the Milky Way's
own Galactoseismic history will therefore serve as a critical foundation for
studying the weak dynamical interactions of galaxies across the universe.Comment: 20 pages, 5 figures, accepted in for publication in a special edition
of the journal "Galaxies", reporting the proceedings of the conference "On
the Origin (and Evolution) of Baryonic Galaxy Halos", Puerto Ayora, Ecuador,
March 13-17 2017, Eds. Duncan A. Forbes and Ericson D. Lope
Pre-freezing of multifractal exponents in Random Energy Models with logarithmically correlated potential
Boltzmann-Gibbs measures generated by logarithmically correlated random
potentials are multifractal. We investigate the abrupt change ("pre-freezing")
of multifractality exponents extracted from the averaged moments of the measure
- the so-called inverse participation ratios. The pre-freezing can be
identified with termination of the disorder-averaged multifractality spectrum.
Naive replica limit employed to study a one-dimensional variant of the model is
shown to break down at the pre-freezing point. Further insights are possible
when employing zero-dimensional and infinite-dimensional versions of the
problem. In particular, the latter version allows one to identify the pattern
of the replica symmetry breaking responsible for the pre-freezing phenomenon.Comment: This is published version, 11 pages, 1 figur
Rigorous confidence intervals for critical probabilities
We use the method of Balister, Bollobas and Walters to give rigorous 99.9999%
confidence intervals for the critical probabilities for site and bond
percolation on the 11 Archimedean lattices. In our computer calculations, the
emphasis is on simplicity and ease of verification, rather than obtaining the
best possible results. Nevertheless, we obtain intervals of width at most
0.0005 in all cases
Boundary conformal field theories and loop models
We propose a systematic method to extract conformal loop models for rational
conformal field theories (CFT). Method is based on defining an ADE model for
boundary primary operators by using the fusion matrices of these operators as
adjacency matrices. These loop models respect the conformal boundary
conditions. We discuss the loop models that can be extracted by this method for
minimal CFTs and then we will give dilute O(n) loop models on the square
lattice as examples for these loop models. We give also some proposals for WZW
SU(2) models.Comment: 23 Pages, major changes! title change
Exploring Halo Substructure with Giant Stars. XV. Discovery of a Connection between the Monoceros Ring and the Triangulum-Andromeda Overdensity?
Thanks to modern sky surveys, over twenty stellar streams and overdensity
structures have been discovered in the halo of the Milky Way. In this paper, we
present an analysis of spectroscopic observations of individual stars from one
such structure, "A13", first identified as an overdensity using the M giant
catalog from the Two Micron All-Sky Survey. Our spectroscopic observations show
that stars identified with A13 have a velocity dispersion of 40
, implying that it is a genuine coherent structure rather
than a chance super-position of random halo stars. From its position on the
sky, distance (15~kpc heliocentric), and kinematical properties, A13 is
likely to be an extension of another low Galactic latitude substructure -- the
Galactic Anticenter Stellar Structure (also known as the Monoceros Ring) --
towards smaller Galactic longitude and farther distance. Furthermore, the
kinematics of A13 also connect it with another structure in the southern
Galactic hemisphere -- the Triangulum-Andromeda overdensity. We discuss these
three connected structures within the context of a previously proposed scenario
that one or all of these features originate from the disk of the Milky Way.Comment: 12 pages, 9 figures. Accepted for publication in Ap
Critical curves in conformally invariant statistical systems
We consider critical curves -- conformally invariant curves that appear at
critical points of two-dimensional statistical mechanical systems. We show how
to describe these curves in terms of the Coulomb gas formalism of conformal
field theory (CFT). We also provide links between this description and the
stochastic (Schramm-) Loewner evolution (SLE). The connection appears in the
long-time limit of stochastic evolution of various SLE observables related to
CFT primary fields. We show how the multifractal spectrum of harmonic measure
and other fractal characteristics of critical curves can be obtained.Comment: Published versio
Conformal Curves in Potts Model: Numerical Calculation
We calculated numerically the fractal dimension of the boundaries of the
Fortuin-Kasteleyn clusters of the -state Potts model for integer and
non-integer values of on the square lattice.
In addition we calculated with high accuracy the fractal dimension of the
boundary points of the same clusters on the square domain. Our calculation
confirms that this curves can be described by SLE.Comment: 11 Pages, 4 figure
Loop models for CFTs
By interpreting the fusion matrix as an adjacency matrix we associate a loop
model to every primary operator of a generic conformal field theory. The weight
of these loop models is given by the quantum dimension of the corresponding
primary operator. Using the known results for the O(n) models we establish a
relationship between these models and SLEs. The method is applied to WZW,
minimal conformal field theories and other coset models.Comment: 24 pages, 4 figures, published version, minor change
- …