38,879 research outputs found
The Opacity of the Intergalactic Medium Measured Along Quasar Sightlines at
We publicly release a new sample of medium resolution quasar spectra at
observed with the Echellette Spectrograph and
Imager (ESI) on the Keck telescope. This quasar sample represents an ideal
laboratory to study the intergalactic medium (IGM) during the end stages of the
epoch of reionization, and constrain the timing and morphology of the phase
transition. For a subset of of our highest signal-to-noise ratio spectra
(S/N, per pixel), we present a new measurement of
the Lyman- (Ly) forest opacity spanning the redshift range
. We carefully eliminate spectral regions that could
be causing biases in our measurements due to additional transmitted flux in the
proximity zone of the quasars, or extra absorption caused by strong intervening
absorption systems along the line of sight. We compare the observed evolution
of the IGM opacity with redshift to predictions from a hydrodynamical
simulation with uniform ultraviolet background (UVB) radiation, as well as two
semi-numerical patchy reionization models, one with a fluctuating UVB and
another with a fluctuating temperature field. Our measurements show a steep
rise in opacity at and an increased scatter and thus support the
picture of a spatially inhomogeneous reionization process, consistent with
previous work. However, we measure significantly higher optical depths at
than previous studies, which reduces the contrast
between the highest opacity Gunn-Peterson troughs and the average opacity trend
of the IGM, which may relieve some of the previously noted tension between
these measurements and reionization models.Comment: accepted for publication at Ap
Inhomogeneous Reionization Models in Cosmological Hydrodynamical Simulations
In this work we present a new hybrid method to simulate the thermal effects
of the reionization in cosmological hydrodynamical simulations. The method
improves upon the standard approach used in simulations of the intergalactic
medium (IGM) and galaxy formation without a significant increase of the
computational cost allowing for efficient exploration of the parameter space.
The method uses a small set of phenomenological input parameters and combines a
semi-numerical reionization model to solve for the topology of reionization and
an approximate model of how reionization heats the IGM, with the massively
parallel \texttt{Nyx} hydrodynamics code, specifically designed to solve for
the structure of diffuse IGM gas. We have produced several large-scale high
resolution cosmological hydrodynamical simulations (, Mpc/h) with different instantaneous and inhomogeneous HI reionization
models that use this new methodology. We study the IGM thermal properties of
these models and find that large scale temperature fluctuations extend well
beyond the end of reionization. Analyzing the 1D flux power spectrum of these
models, we find up to differences in the large scale properties
(low modes, s/km) of the post-reionization power spectrum due
to the thermal fluctuations. We show that these differences could allow one to
distinguish between different reionization scenarios already with existing
Ly forest measurements. Finally, we explore the differences in the
small-scale cutoff of the power spectrum and we find that, for the same heat
input, models show very good agreement provided that the reionization redshift
of the instantaneous reionization model happens at the midpoint of the
inhomogeneous model.Comment: 24 pages, 16 figures. Accepted by MNRAS. Minor changes to match
published versio
Brown dwarf populations in open clusters
We present the results of multiple simulations of open clusters, modelling
the dynamics of a population of brown dwarf members. We consider the effects of
a large range of primordial binary populations, including the possibilities of
having brown dwarf members contained within a binary system. We also examine
the effects of various cluster diameters and masses. Our examination of a
population of wide binary systems containing brown dwarfs, reveals evidence for
exchange reactions whereby the brown dwarf is ejected from the system and
replaced by a heavier main-sequence star. We find that there exists the
possibility of hiding a large fraction of the brown dwarfs contained within the
primordial binary population. We conclude that it is probable that the majority
of brown dwarfs are contained within primordial binary systems which then hides
a large proportion of them from detection.Comment: 16 pages, 8 figures; to appear in MNRA
Fundamental length in quantum theories with PT-symmetric Hamiltonians
The direct observability of coordinates x is often lost in PT-symmetric
quantum theories. A manifestly non-local Hilbert-space metric enters
the double-integral normalization of wave functions there. In the
context of scattering, the (necessary) return to the asymptotically fully local
metric has been shown feasible, for certain family of PT-symmetric toy
Hamiltonians H at least, in paper I (M. Znojil, Phys. Rev. D 78 (2008) 025026).
Now we show that in a confined-motion dynamical regime the same toy model
proves also suitable for an explicit control of the measure or width
of its non-locality. For this purpose each H is assigned here, constructively,
the complete menu of its hermitizing metrics
distinguished by their optional "fundamental lengths" .
The local metric of paper I recurs at while the most popular
CPT-symmetric hermitization proves long-ranged, with .Comment: 31 pp, 3 figure
Ergodic property of Markovian semigroups on standard forms of von Neumann algebras
We give sufficient conditions for ergodicity of the Markovian semigroups
associated to Dirichlet forms on standard forms of von Neumann algebras
constructed by the method proposed in Refs. [Par1,Par2]. We apply our result to
show that the diffusion type Markovian semigroups for quantum spin systems are
ergodic in the region of high temperatures where the uniqueness of the
KMS-state holds.Comment: 25 page
The effect of stellar-mass black holes on the structural evolution of massive star clusters
We present the results of realistic N-body modelling of massive star clusters
in the Magellanic Clouds, aimed at investigating a dynamical origin for the
radius-age trend observed in these systems. We find that stellar-mass black
holes, formed in the supernova explosions of the most massive cluster stars,
can constitute a dynamically important population. If a significant number of
black holes are retained (here we assume complete retention), these objects
rapidly form a dense core where interactions are common, resulting in the
scattering of black holes into the cluster halo, and the ejection of black
holes from the cluster. These two processes heat the stellar component,
resulting in prolonged core expansion of a magnitude matching the observations.
Significant core evolution is also observed in Magellanic Cloud clusters at
early times. We find that this does not result from the action of black holes,
but can be reproduced by the effects of mass-loss due to rapid stellar
evolution in a primordially mass segregated cluster.Comment: Accepted for publication in MNRAS Letters; 2 figures, 1 tabl
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