1,028 research outputs found
The stellar populations of the central region of M31
We continue the analysis of the dataset of our spectroscopic observation
campaign of M31, by deriving simple stellar population properties (age
metallicity and alpha-elements overabundance) from the measurement of Lick/IDS
absorption line indices. We describe their two-dimensional maps taking into
account the dust distribution in M31. 80\% of the values of our age
measurements are larger than 10 Gyr. The central 100 arcsec of M31 are
dominated by the stars of the classical bulge of M31. They are old (11-13 Gyr),
metal-rich (as high as [Z/H]~0.35 dex) at the center with a negative gradient
outwards and enhanced in alpha-elements ([alpha/Fe]~ 0.28+- 0.01 dex). The bar
stands out in the metallicity map, where an almost solar value of [Z/H]
(~0.02+-0.01 dex) with no gradient is observed along the bar position angle
(55.7 deg) out to 600 arcsec from the center. In contrast, no signature of the
bar is seen in the age and [alpha/Fe] maps, that are approximately
axisymmetric, delivering a mean age and overabundance for the bar and the
boxy-peanut bulge of 10-13 Gyr and 0.25-0.27 dex, respectively. The
boxy/peanut-bulge has almost solar metallicity (-0.04+- 0.01 dex). The
mass-to-light ratio of the three components is approximately constant at M/LV ~
4.4-4.7 Msol/Lsol. The disk component at larger distances is made of a mixture
of stars, as young as 3-4 Gyr, with solar metallicity and smaller M/LV (~3+-0.1
Msol/Lsol). We propose a two-phase formation scenario for the inner region of
M31, where most of the stars of the classical bulge come into place together
with a proto-disk, where a bar develops and quickly transforms it into a
boxy-peanut bulge. Star formation continues in the bulge region, producing
stars younger than 10 Gyr, in particular along the bar, enhancing its
metallicity. The disk component appears to build up on longer time-scales.Comment: Language-edited version, Accepted for publication in A&
XXZ Bethe states as highest weight vectors of the loop algebra at roots of unity
We show that every regular Bethe ansatz eigenvector of the XXZ spin chain at
roots of unity is a highest weight vector of the loop algebra, for some
restricted sectors with respect to eigenvalues of the total spin operator
, and evaluate explicitly the highest weight in terms of the Bethe roots.
We also discuss whether a given regular Bethe state in the sectors generates an
irreducible representation or not. In fact, we present such a regular Bethe
state in the inhomogeneous case that generates a reducible Weyl module. Here,
we call a solution of the Bethe ansatz equations which is given by a set of
distinct and finite rapidities {\it regular Bethe roots}. We call a nonzero
Bethe ansatz eigenvector with regular Bethe roots a {\it regular Bethe state}.Comment: 40pages; revised versio
The old and heavy bulge of M31 I. Kinematics and stellar populations
We present new optical long-slit data along 6 position angles of the bulge
region of M31. We derive accurate stellar and gas kinematics reaching 5 arcmin
from the center, where the disk light contribution is always less than 30%, and
out to 8 arcmin along the major axis, where the disk makes 55% of the total
light. We show that the velocity dispersions of McElroy (1983) are severely
underestimated (by up to 50 km/s) and previous dynamical models have
underestimated the stellar mass of M31's bulge by a factor 2. Moreover, the
light-weighted velocity dispersion of the galaxy grows to 166 km/s, thus
reducing the discrepancy between the predicted and measured mass of the black
hole at the center of M31. The kinematic position angle varies with distance,
pointing to triaxiality. We detect gas counterrotation near the bulge minor
axis. We measure eight emission-corrected Lick indices. They are approximately
constant on circles. We derive the age, metallicity and alpha-element
overabundance profiles. Except for the region in the inner arcsecs of the
galaxy, the bulge of M31 is uniformly old (>12 Gyr, with many best-fit ages at
the model grid limit of 15 Gyr), slightly alpha-elements overabundant
([alpha/Fe]~0.2) and at solar metallicity, in agreement with studies of the
resolved stellar components. The predicted u-g, g-r and r-i Sloan color
profiles match reasonably well the dust-corrected observations. The stellar
populations have approximately radially constant mass-to-light ratios (M/L_R ~
4-4.5 for a Kroupa IMF), in agreement with stellar dynamical estimates based on
our new velocity dispersions. In the inner arcsecs the luminosity-weighted age
drops to 4-8 Gyr, while the metallicity increases to above 3 times the solar
value.Comment: Accepted for publication in A&
Chapter 17: Vulnerability of coral reefs of the Great Barrier Reef to climate change
The Great Barrier Reef (GBR) contains the most extensive coral reef ecosystem on earth. It consists of
2900 coral reefs and 900 coral cays that cover approximately 20,000 km2 of the total 345,000 km2
area of the GBR Marine Park. As a consequence of unusually high summer sea surface temperatures,
between 42 to 60 percent of the reefs of the GBR experienced mass coral bleaching in 19988.
Bleaching was also reported from 31 other nations around the world during 1997–1998. For example,
about 50 percent of reefs in the Indian Ocean and south Asia lost much of their coral cover, and an
estimated 16 percent of the world’s area of coral reefs was severely damaged. The event coincided
with the strongest recorded El Niño-Southern Oscillation event (ENSO) and one of the warmest years
on record.This is Chapter 17 of Climate change and the Great Barrier Reef: a vulnerability assessment. The entire book can be found at http://hdl.handle.net/11017/13
String Breaking in Non-Abelian Gauge Theories with Fundamental Matter Fields
We present clear numerical evidence for string breaking in three-dimensional
SU(2) gauge theory with fundamental bosonic matter through a mixing analysis
between Wilson loops and meson operators representing bound states of a static
source and a dynamical scalar. The breaking scale is calculated in the
continuum limit. In units of the lightest glueball we find . The implications of our results for QCD are discussed.Comment: 4 pages, 2 figures; equations (4)-(6) corrected, numerical results
and conclusions unchange
Scalar-gauge dynamics in (2+1) dimensions at small and large scalar couplings
We present the results of a detailed calculation of the excitation spectrum
of states with quantum numbers J^{PC}=0++, 1-- and 2++ in the three-dimensional
SU(2) Higgs model at two values of the scalar self-coupling and for fixed gauge
coupling. In the context of studies of the electroweak phase transition at
finite temperature these couplings correpond to tree-level, zero temperature
Higgs masses of 35 GeV and 120 GeV, respectively. We also study the properties
of Polyakov loop operators, which serve to test the confining properties of the
model in the symmetric phase. At both values of the scalar coupling we obtain
masses of bound states consisting entirely of gauge degrees of freedom
("W-balls"), which are very close to those obtained in the pure gauge theory.
We conclude that the previously observed, approximate decoupling of the scalar
and gauge sectors of the theory persists at large scalar couplings. We study
the crossover region at large scalar coupling and present a scenario how the
confining properties of the model in the symmetric phase are lost inside the
crossover by means of flux tube decay. We conclude that the underlying dynamics
responsible for the observed dense spectrum of states in the Higgs region at
large couplings must be different from that in the symmetric phase.Comment: 36 pages, LaTeX, 13 postscript files, to be included with epsf;
improved presentation, updated references, conclusions unchanged; version to
appear in Nucl. Phys.
The spectrum of the three-dimensional adjoint Higgs model and hot SU(2) gauge theory
We compute the mass spectrum of the SU(2) adjoint Higgs model in 2+1
dimensions at several points located in the (metastable) confinement region of
its phase diagram. We find a dense spectrum consisting of an almost unaltered
repetition of the glueball spectrum of the pure gauge theory, and additional
bound states of adjoint scalars. For the parameters chosen, the model
represents the effective finite temperature theory for pure SU(2) gauge theory
in four dimensions, obtained after perturbative dimensional reduction.
Comparing with the spectrum of screening masses obtained in recent simulations
of four-dimensional pure gauge theory at finite temperature, for the low lying
states we find quantitative agreement between the full and the effective theory
for temperatures as low as T = 2 Tc. This establishes the model under study as
the correct effective theory, and dimensional reduction as a viable tool for
the description of thermodynamic properties. We furthermore compare the
perturbative contribution O(g.T) with the non-perturbative contributions
O(g^2.T) and O(g^3.T) to the Debye mass. The latter turns out to be dominated
by the scale g^2.T, whereas higher order contributions are small corrections.Comment: LaTeX. Typos corrected and references adde
Irreducibility criterion for a finite-dimensional highest weight representation of the sl(2) loop algebra and the dimensions of reducible representations
We present a necessary and sufficient condition for a finite-dimensional
highest weight representation of the loop algebra to be irreducible. In
particular, for a highest weight representation with degenerate parameters of
the highest weight, we can explicitly determine whether it is irreducible or
not. We also present an algorithm for constructing finite-dimensional highest
weight representations with a given highest weight. We give a conjecture that
all the highest weight representations with the same highest weight can be
constructed by the algorithm. For some examples we show the conjecture
explicitly. The result should be useful in analyzing the spectra of integrable
lattice models related to roots of unity representations of quantum groups, in
particular, the spectral degeneracy of the XXZ spin chain at roots of unity
associated with the loop algebra.Comment: 32 pages with no figure; with corrections on the published versio
17O NMR study of q=0 spin excitations in a nearly ideal S=1/2 1D Heisenberg antiferromagnet, Sr2CuO3, up to 800 K
We used 17O NMR to probe the uniform (wavevector q=0) electron spin
excitations up to 800 K in Sr2CuO3 and separate the q=0 from the q=\pm\pi/a
staggered components. Our results support the logarithmic decrease of the
uniform spin susceptibility below T ~ 0.015J, where J=2200 K. From measurement
of the dynamical spin susceptibility for q=0 by the spin-lattice relaxation
rate 1/T_{1}, we demonstrate that the q=0 mode of spin transport is ballistic
at the T=0 limit, but has a diffusion-like contribution at finite temperatures
even for T << J.Comment: Submitted to Phys. Rev. Lett. 4 pages, 4 figure
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