14,989 research outputs found
Power Boosts for Cluster Tests
Abstract. Gene cluster significance tests that are based on the num-ber of genes in a cluster in two genomes, and how compactly they are distributed, but not their order, may be made more powerful by the ad-dition of a test component that focuses solely on the similarity of the ordering of the common genes in the clusters in the two genomes. Here we suggest four such tests, compare them, and investigate one of them, the maximum adjacency disruption criterion, in some detail, analytically and through simulation.
Defining the frame of minimum nonlinear Hubble expansion variation
We characterize a cosmic rest frame in which the monopole variation of the
spherically averaged nonlinear Hubble expansion is most uniform, under
arbitrary local Lorentz boosts of the central observer. Using the COMPOSITE
sample of 4534 galaxies, we identify a degenerate set of candidate minimum
nonlinear variation frames, which includes the rest frame of the Local Group
(LG) of galaxies, but excludes the standard Cosmic Microwave Background (CMB)
frame. Candidate rest frames defined by a boost from the LG frame close to the
plane of the galaxy have a statistical likelihood similar to the LG frame. This
may result from a lack of constraining data in the Zone of Avoidance. We extend
our analysis to the Cosmicflows-2 (CF2) sample of 8162 galaxies. While the
signature of a systematic boost offset between the CMB and LG frame averages is
still detected, the spherically averaged nonlinear expansion variation in all
rest frames is significantly larger in the CF2 sample than would be reasonably
expected. We trace this to the CF2 distances being reported without a
correction for inhomogeneous distribution Malmquist bias. Systematic
differences in the inclusion of the large SFI++ subsample into the COMPOSITE
and CF2 catalogues are analysed. Our results highlight the importance of a
careful treatment of Malmquist biases for future peculiar velocities studies,
including tests of the hypothesis of Wiltshire et al [Phys. Rev. D 88 (2013)
083529; arXiv:1201.5371] that a significant fraction of the CMB temperature
dipole may be nonkinematic in origin.Comment: 25 pages, 19 figures; v4 erratum added: small corrections, no change
in conclusion
The Impact of Cluster Structure and Dynamical State on Scatter in the Sunyaev-Zel'dovich Flux-Mass Relation
Cosmological constraints from cluster surveys rely on accurate mass estimates
from the mass-observable relations. In order to avoid systematic biases and
reduce uncertainties, we study the form and physical origin of the intrinsic
scatter about the mean Sunyaev-Zel'dovich (SZ) flux-mass relation using a
hydrodynamical simulation of galaxy cluster formation. We examine the
assumption of lognormal scatter and detect non-negligible positive skewness and
kurtosis (> 0.5) for a wide range of limiting masses and redshifts. These
higher-order moments should be included in the parametrization of scatter in
order not to bias cosmological constraints. We investigate the sources of the
scatter by correlating it with measures of cluster morphology, halo
concentration, and dynamical state, and we quantify the individual contribution
from each source. We find that statistically the impact of dynamical state is
weak, so the selection bias due to mergers is negligible. On the other hand,
there is a strong correlation between the scatter and halo concentration, which
can be used to reduce the scatter significantly (from 12.07% to 7.34% or by
~40% for clusters at z = 0). We also show that a cross-calibration by combining
information from X-ray followups can be used to reduce the scatter in the
flux-mass relation and also identify outliers in both X-ray and SZ cluster
surveys.Comment: 14 pages, 12 figures; accepted for publication in Ap
Effect of Our Galaxy's Motion on Weak Lensing Measurements of Shear and Convergence
In this work we investigate the effect on weak-lensing shear and convergence
measurements due to distortions from the Lorentz boost induced by our Galaxy's
motion. While no ellipticity is induced in an image from the Lorentz boost to
first order in beta = v/c, the image is magnified. This affects the inferred
convergence at a 10 per cent level, and is most notable for low multipoles in
the convergence power spectrum C {\kappa}{\kappa} and for surveys with large
sky coverage like LSST and DES. Experiments which image only small fractions of
the sky and convergence power spectrum determinations at l > 5 can safely
neglect the boost effect to first order in beta.Comment: 4 pages, replaced to reflect changes made for publication to MNRA
Observational Challenges for the Standard FLRW Model
We summarise some of the main observational challenges for the standard
Friedmann-Lemaitre-Robertson-Walker cosmological model and describe how results
recently presented in the parallel session `Large--scale Structure and
Statistics' (DE3) at the `Fourteenth Marcel Grossman Meeting on General
Relativity' are related to these challenges.Comment: 17 pages; references added. Matches published version in Int. J. Mod.
Phys. D; Report on Parallel Session DE3 of MG1
Separating intrinsic alignment and galaxy-galaxy lensing
The coherent physical alignment of galaxies is an important systematic for
gravitational lensing studies as well as a probe of the physical mechanisms
involved in galaxy formation and evolution. We develop a formalism for treating
this intrinsic alignment (IA) in the context of galaxy-galaxy lensing and
present an improved method for measuring IA contamination, which can arise when
sources physically associated with the lens are placed behind the lens due to
photometric redshift scatter. We apply the technique to recent Sloan Digital
Sky Survey (SDSS) measurements of Luminous Red Galaxy lenses and typical (L*)
source galaxies with photometric redshifts selected from the SDSS imaging data.
Compared to previous measurements, this method has the advantage of being fully
self-consistent in its treatment of the IA and lensing signals, solving for the
two simultaneously. We find an IA signal consistent with zero, placing tight
constraints on both the magnitude of the IA effect and its potential
contamination to the lensing signal. While these constraints depend on source
selection and redshift quality, the method can be applied to any measurement
that uses photometric redshifts. We obtain a model-independent upper-limit of
roughly 10% IA contamination for projected separations of approximately 0.1-100
Mpc/h. With more stringent photo-z cuts and reasonable assumptions about the
physics of intrinsic alignments, this upper limit is reduced to 1-2%. These
limits are well below the statistical error of the current lensing
measurements. Our results suggest that IA will not present intractable
challenges to the next generation of galaxy-galaxy lensing experiments, and the
methods presented here should continue to aid in our understanding of alignment
processes and in the removal of IA from the lensing signal.Comment: 31 pages, 8 Figures. Minor changes to reflect published versio
Disentangling cosmic-ray and dark-matter induced gamma-rays in galaxy clusters?
Galaxy clusters are among the best targets for indirect dark matter detection
in gamma-rays, despite the large astrophysical background expected from these
objects. Detection is now within reach of current observatories (Fermi-LAT or
Cerenkov telescopes); however, assessing the origin of this signal might be
difficult. We investigate whether the behaviour of the number of objects per
`flux' bin (logN-logF) and that of the stacked signal could be used as a
signature of the dominant process at stake.We use the CLUMPY code to integrate
the signal from decaying or annihilating dark matter and cosmic rays along the
line of sight. We assume the standard NFW profile for the dark matter density
and rely on a parametrised emissivity for the cosmic-ray component. In this
context, the consequences of stacking are explored using the MCXC
meta-catalogue of galaxy clusters. We find the value of the slope of the
logN-logF power law (or the increase of the signal with the number of stacked
objects) to be a clear diagnosis to disentangle decaying dark matter from
cosmic-ray induced gamma-rays. For dark matter annihilation, depending on the
signal boost from the substructures, it is either similar to the cosmic-ray
signal (no boost) or similar to the decay case (large boosts). The shift
between the brightest object and its followers also depends on the signal
origin. For annihilation, this shift and the stacked signal are poorly
constrained because of the large uncertainty affecting the boost. We also
underline that the angular dependence of the annihilation signal is not
universal because of the substructure contribution.Comment: 7 pages, 3 figures, minor corrections (to match the A&A accepted
version
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