8,609 research outputs found
Census of Planar Maps: From the One-Matrix Model Solution to a Combinatorial Proof
We consider the problem of enumeration of planar maps and revisit its
one-matrix model solution in the light of recent combinatorial techniques
involving conjugated trees. We adapt and generalize these techniques so as to
give an alternative and purely combinatorial solution to the problem of
counting arbitrary planar maps with prescribed vertex degrees.Comment: 29 pages, 14 figures, tex, harvmac, eps
All-Helicity Symbol Alphabets from Unwound Amplituhedra
We review an algorithm for determining the branch points of general
amplitudes in planar super-Yang-Mills theory from amplituhedra.
We demonstrate how to use the recent reformulation of amplituhedra in terms of
`sign flips' in order to streamline the application of this algorithm to
amplitudes of any helicity. In this way we recover the known branch points of
all one-loop amplitudes, and we find an `emergent positivity' on boundaries of
amplituhedra.Comment: 38 pages, 5 figures, 1 big table; v2: minor corrections and
improvement
Classification and analysis of emission-line galaxies using mean field independent component analysis
We present an analysis of the optical spectra of narrow emission-line
galaxies, based on mean field independent component analysis (MFICA). Samples
of galaxies were drawn from the Sloan Digital Sky Survey (SDSS) and used to
generate compact sets of `continuum' and `emission-line' component spectra.
These components can be linearly combined to reconstruct the observed spectra
of a wider sample of galaxies. Only 10 components - five continuum and five
emission line - are required to produce accurate reconstructions of essentially
all narrow emission-line galaxies; the median absolute deviations of the
reconstructed emission-line fluxes, given the signal-to-noise ratio (S/N) of
the observed spectra, are 1.2-1.8 sigma for the strong lines. After applying
the MFICA components to a large sample of SDSS galaxies we identify the regions
of parameter space that correspond to pure star formation and pure active
galactic nucleus (AGN) emission-line spectra, and produce high S/N
reconstructions of these spectra.
The physical properties of the pure star formation and pure AGN spectra are
investigated by means of a series of photoionization models, exploiting the
faint emission lines that can be measured in the reconstructions. We are able
to recreate the emission line strengths of the most extreme AGN case by
assuming the central engine illuminates a large number of individual clouds
with radial distance and density distributions, f(r) ~ r^gamma and g(n) ~
n^beta, respectively. The best fit is obtained with gamma = -0.75 and beta =
-1.4. From the reconstructed star formation spectra we are able to estimate the
starburst ages. These preliminary investigations serve to demonstrate the
success of the MFICA-based technique in identifying distinct emission sources,
and its potential as a tool for the detailed analysis of the physical
properties of galaxies in large-scale surveys.Comment: MNRAS accepted. 29 pages, 24 figures, 3 table
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