4,240 research outputs found
Bayes-X: a Bayesian inference tool for the analysis of X-ray observations of galaxy clusters
We present the first public release of our Bayesian inference tool, Bayes-X,
for the analysis of X-ray observations of galaxy clusters. We illustrate the
use of Bayes-X by analysing a set of four simulated clusters at z=0.2-0.9 as
they would be observed by a Chandra-like X-ray observatory. In both the
simulations and the analysis pipeline we assume that the dark matter density
follows a spherically-symmetric Navarro, Frenk and White (NFW) profile and that
the gas pressure is described by a generalised NFW (GNFW) profile. We then
perform four sets of analyses. By numerically exploring the joint probability
distribution of the cluster parameters given simulated Chandra-like data, we
show that the model and analysis technique can robustly return the simulated
cluster input quantities, constrain the cluster physical parameters and reveal
the degeneracies among the model parameters and cluster physical parameters. We
then analyse Chandra data on the nearby cluster, A262, and derive the cluster
physical profiles. To illustrate the performance of the Bayesian model
selection, we also carried out analyses assuming an Einasto profile for the
matter density and calculated the Bayes factor. The results of the model
selection analyses for the simulated data favour the NFW model as expected.
However, we find that the Einasto profile is preferred in the analysis of A262.
The Bayes-X software, which is implemented in Fortran 90, is available at
http://www.mrao.cam.ac.uk/facilities/software/bayesx/.Comment: 22 pages, 11 figure
Galaxy Cluster Pressure Profiles as Determined by Sunyaev Zel'dovich Effect Observations with MUSTANG and Bolocam I: Joint Analysis Technique
We present a technique to constrain galaxy cluster pressure profiles by
jointly fitting Sunyaev-Zel'dovich effect (SZE) data obtained with MUSTANG and
Bolocam for the clusters Abell 1835 and MACS0647. Bolocam and MUSTANG probe
different angular scales and are thus highly complementary. We find that the
addition of the high resolution MUSTANG data can improve constraints on
pressure profile parameters relative to those derived solely from Bolocam. In
Abell 1835 and MACS0647, we find gNFW inner slopes of and , respectively when
and are constrained to 0.86 and 4.67 respectively. The fitted
SZE pressure profiles are in good agreement with X-ray derived pressure
profiles.Comment: 12 pages, 12 figures. Submitted to Ap
Planck/SDSS Cluster Mass and Gas Scaling Relations for a Volume-Complete redMaPPer Sample
Using Planck satellite data, we construct SZ gas pressure profiles for a
large, volume-complete sample of optically selected clusters. We have defined a
sample of over 8,000 redMaPPer clusters from the Sloan Digital Sky Survey
(SDSS), within the volume-complete redshift region 0.100 < z < 0.325, for which
we construct Sunyaev-Zel'dovich (SZ) effect maps by stacking Planck data over
the full range of richness. Dividing the sample into richness bins we
simultaneously solve for the mean cluster mass in each bin together with the
corresponding radial pressure profile parameters, employing an MCMC analysis.
These profiles are well detected over a much wider range of cluster mass and
radius than previous work, showing a clear trend towards larger break radius
with increasing cluster mass. Our SZ-based masses fall ~24% below the
mass-richness relations from weak lensing, in a similar fashion as the
"hydrostatic bias" related with X-ray derived masses. We correct for this bias
to derive an optimal mass-richness relation finding a slope 1.22 +/- 0.04 and a
pivot mass log(M_500/M_0)= 14.432 +/- 0.041, evaluated at a richness lambda=60.
Finally, we derive a tight Y_500-M_500 relation over a wide range of cluster
mass, with a power law slope equal to 1.72 +/- 0.07, that agrees well with the
independent slope obtained by the Planck team with an SZ-selected cluster
sample, but extends to lower masses with higher precision.Comment: 13 pages, 7 figure
Planck/SDSS Cluster Mass and Gas Scaling Relations for a Volume-Complete redMaPPer Sample
Using Planck satellite data, we construct SZ gas pressure profiles for a
large, volume-complete sample of optically selected clusters. We have defined a
sample of over 8,000 redMaPPer clusters from the Sloan Digital Sky Survey
(SDSS), within the volume-complete redshift region 0.100 < z < 0.325, for which
we construct Sunyaev-Zel'dovich (SZ) effect maps by stacking Planck data over
the full range of richness. Dividing the sample into richness bins we
simultaneously solve for the mean cluster mass in each bin together with the
corresponding radial pressure profile parameters, employing an MCMC analysis.
These profiles are well detected over a much wider range of cluster mass and
radius than previous work, showing a clear trend towards larger break radius
with increasing cluster mass. Our SZ-based masses fall ~24% below the
mass-richness relations from weak lensing, in a similar fashion as the
"hydrostatic bias" related with X-ray derived masses. We correct for this bias
to derive an optimal mass-richness relation finding a slope 1.22 +/- 0.04 and a
pivot mass log(M_500/M_0)= 14.432 +/- 0.041, evaluated at a richness lambda=60.
Finally, we derive a tight Y_500-M_500 relation over a wide range of cluster
mass, with a power law slope equal to 1.72 +/- 0.07, that agrees well with the
independent slope obtained by the Planck team with an SZ-selected cluster
sample, but extends to lower masses with higher precision.Comment: 13 pages, 7 figure
Boundary Ring: a way to construct approximate NG solutions with polygon boundary conditions: I. Z_n-symmetric configurations
We describe an algebro-geometric construction of polygon-bounded minimal
surfaces in ADS_5, based on consideration of what we call the "boundary ring"
of polynomials. The first non-trivial example of the Nambu-Goto (NG) solutions
for Z_6-symmetric hexagon is considered in some detail. Solutions are
represented as power series, of which only the first terms are evaluated. The
NG equations leave a number of free parameters (a free function). Boundary
conditions, which fix the free parameters, are imposed on truncated series. It
is still unclear if explicit analytic formulas can be found in this way, but
even approximate solutions, obtained by truncation of power series, can be
sufficient to investigate the Alday-Maldacena -- BDS/BHT version of the
string/gauge duality.Comment: 42 pages, 5 figure
Progressive Label Distillation: Learning Input-Efficient Deep Neural Networks
Much of the focus in the area of knowledge distillation has been on
distilling knowledge from a larger teacher network to a smaller student
network. However, there has been little research on how the concept of
distillation can be leveraged to distill the knowledge encapsulated in the
training data itself into a reduced form. In this study, we explore the concept
of progressive label distillation, where we leverage a series of
teacher-student network pairs to progressively generate distilled training data
for learning deep neural networks with greatly reduced input dimensions. To
investigate the efficacy of the proposed progressive label distillation
approach, we experimented with learning a deep limited vocabulary speech
recognition network based on generated 500ms input utterances distilled
progressively from 1000ms source training data, and demonstrated a significant
increase in test accuracy of almost 78% compared to direct learning.Comment: 9 page
Quantum transport through single and multilayer icosahedral fullerenes
We use a tight-binding Hamiltonian and Green functions methods to calculate
the quantum transmission through single-wall fullerenes and bilayered and
trilayered onions of icosahedral symmetry attached to metallic leads. The
electronic structure of the onion-like fullerenes takes into account the
curvature and finite size of the fullerenes layers as well as the strength of
the intershell interactions depending on to the number of interacting atom
pairs belonging to adjacent shells. Misalignment of the symmetry axes of the
concentric icosahedral shells produces breaking of the level degeneracies of
the individual shells, giving rise some narrow quasi-continuum bands instead of
the localized discrete peaks of the individual fullerenes. As a result, the
transmission function for non symmetrical onions are rapidly varying functions
of the Fermi energy. Furthermore, we found that most of the features of the
transmission through the onions are due to the electronic structure of the
outer shell with additional Fano-like antiresonances arising from coupling with
or between the inner shells.Comment: 16 pages, 5 figur
A Comparison and Joint Analysis of Sunyaev-Zel'dovich Effect Measurements from Planck and Bolocam for a set of 47 Massive Galaxy Clusters
We measure the SZ signal toward a set of 47 clusters with a median mass of
M and a median redshift of 0.40 using data from
Planck and the ground-based Bolocam receiver. When Planck XMM-like masses are
used to set the scale radius , we find consistency between
the integrated SZ signal, , derived from Bolocam and Planck
based on gNFW model fits using A10 shape parameters, with an average ratio of
(allowing for the % Bolocam flux calibration
uncertainty). We also perform a joint fit to the Bolocam and Planck data using
a modified A10 model with the outer logarithmic slope allowed to vary,
finding (measurement error followed by
intrinsic scatter). In addition, we find that the value of scales with
mass and redshift according to . This mass scaling is in good agreement with recent
simulations. We do not observe the strong trend of with redshift seen
in simulations, though we conclude that this is most likely due to our sample
selection. Finally, we use Bolocam measurements of to test the
accuracy of the Planck completeness estimate. We find consistency, with the
actual number of Planck detections falling approximately below the
expectation from Bolocam. We translate this small difference into a constraint
on the the effective mass bias for the Planck cluster cosmology results, with
.Comment: Updated to include one additional co-author. Also some minor changes
to the text based on initial feedbac
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