410 research outputs found
Cluster richness-mass calibration with cosmic microwave background lensing
This document is the Accepted Manuscript of the following article: James E. Geach, and John A. Peacock, âCluster richnessâmass calibration with cosmic microwave background lensingâ, Nature Astronomy, Vol. 1: 795-799, 2017. Under embargo until 9 April 2018. This manuscript version is made available under Springer Nature terms for reuse, see http://www.nature.com/authors/policies/license.html#terms The final, definitive version of this paper has been published in Nature Astronomy, at doi: https://doi.org/10.1038/s41550-017-0259-1.Identifying galaxy clusters through overdensities of galaxies in photometric surveys is the oldest and arguably the most economic and mass-sensitive detection method, compared to X-ray and Sunyaev-Zel'dovich Effect surveys that detect the hot intracluster medium. However, a perennial problem has been the mapping of optical 'richness' measurements on to total cluster mass. Emitted at a conformal distance of 14 Gpc, the cosmic microwave background acts as a backlight to all intervening mass in the Universe, and therefore has been gravitationally lensed. Here we present a calibration of cluster optical richness at the 10 per cent level by measuring the average cosmic microwave background lensing convergence measured by Planck towards the positions of large numbers of optically-selected clusters, detecting the deflection of photons by haloes of total mass of the order 10**14 solar masses. Although mainly aimed at the study of larger-scale structures, the Planck lensing reconstruction can yield nearly unbiased results for stacked clusters on arcminute scales. The lensing convergence only depends on the redshift integral of the fractional overdensity of matter, so this approach offers a clean measure of cluster mass over most of cosmic history, largely independent of baryon physics.Peer reviewe
The LBDS Hercules sample of mJy radio sources at 1.4 GHz - II. Redshift distribution, radio luminosity function, and the high-redshift cut-off
{Abridged} A combination of spectroscopy and broadband photometric redshifts
has been used to find the complete redshift distribution of the Hercules sample
of millijansky radio sources. These data have been used to examine the
evolution of the radio luminosity function (RLF) and its high-redshift cut-off.
New redshifts have been measured for eleven sources, and a further ten upper
limits are given. The total number of sources with known redshifts in the
sample is now 47 (65%). We calculated broadband photometric redshifts for the
remaining one-third of the sample.
For the luminosity range probed by the present study (P_1.4 > 10^24.5
W/Hz/sr), we use the V/V_max test to show conclusively that there is a deficit
of high-redshift (z > 2-2.5) objects. Comparison with the model RLFs of Dunlop
& Peacock (1990) shows that our data can now exclude pure luminosity evolution.
Two of the models of DP90, and the RLF deduced by direct binning of the data,
both favour a luminosity dependence for the high-redshift cut-off, with
lower-luminosity sources (P_1.4 \simeq 10^24 W/Hz/sr) in decline by z \simeq
1-1.5 while higher-luminosity sources (P_1.4 \simeq 10^{25-26} W/Hz/sr) decline
in comoving number density beyond z \simeq 2-2.5.Comment: Revised version submitted to MNRAS. 16 pages, 12 figure
Constraining dark energy fluctuations with supernova correlations
We investigate constraints on dark energy fluctuations using type Ia
supernovae. If dark energy is not in the form of a cosmological constant, that
is if the equation of state is not equal to -1, we expect not only temporal,
but also spatial variations in the energy density. Such fluctuations would
cause local variations in the universal expansion rate and directional
dependences in the redshift-distance relation. We present a scheme for relating
a power spectrum of dark energy fluctuations to an angular covariance function
of standard candle magnitude fluctuations. The predictions for a
phenomenological model of dark energy fluctuations are compared to
observational data in the form of the measured angular covariance of Hubble
diagram magnitude residuals for type Ia supernovae in the Union2 compilation.
The observational result is consistent with zero dark energy fluctuations.
However, due to the limitations in statistics, current data still allow for
quite general dark energy fluctuations as long as they are in the linear
regime.Comment: 18 pages, 6 figures, matches the published versio
Large extra dimensions, the galaxy power spectrum and the end of inflation
We consider the production of gravitational KK modes via cosmological
photon-photon and electron-positron annihilation in models with large
factorisable extra dimensions. We place constraints on this production using
recent results from a joint analysis of the power spectra of the 2dF Galaxy
Redshift Survey (2dFGS) and the cosmic microwave background (CMB) anisotropies.
We obtain a more accurate upper limit for the temperature corresponding to
matter-radiation equality and show that, even for the case of 6 extra
dimensions and a fundamental scale of 1 TeV, a period of inflation is required
that ends at a temperature much lower than that of the QCD phase transition.Comment: 12 pages, 2 figures, hadronic branching+typos corrected,accepted in
JHE
Entropy of the Universe
After a discussion on several limiting cases where General Relativity turns
into less sophisticated theories, we find that in the correct thermodynamical
and cosmological weak field limit of Einstein's field equations the entropy of
the Universe is R^(3/2) -- dependent, where R stands for the radius of the
causally related Universe. Thus, entropy grows in the Universe, contrary to
Standard Cosmology prediction.Comment: To be published by International Journal of Theoretical Physic
The SCUBA Half Degree Extragalactic Survey (SHADES) - III : Identification of radio and mid-infrared counterparts to submillimetre galaxies
Peer reviewe
Constraining warm dark matter with cosmic shear power spectra
We investigate potential constraints from cosmic shear on the dark matter
particle mass, assuming all dark matter is made up of light thermal relic
particles. Given the theoretical uncertainties involved in making cosmological
predictions in such warm dark matter scenarios we use analytical fits to linear
warm dark matter power spectra and compare (i) the halo model using a mass
function evaluated from these linear power spectra and (ii) an analytical fit
to the non-linear evolution of the linear power spectra. We optimistically
ignore the competing effect of baryons for this work. We find approach (ii) to
be conservative compared to approach (i). We evaluate cosmological constraints
using these methods, marginalising over four other cosmological parameters.
Using the more conservative method we find that a Euclid-like weak lensing
survey together with constraints from the Planck cosmic microwave background
mission primary anisotropies could achieve a lower limit on the particle mass
of 2.5 keV.Comment: 26 pages, 9 figures, minor changes to match the version accepted for
publication in JCA
An Isocurvature Mechanism for Structure Formation
We examine a novel mechanism for structure formation involving initial number
density fluctuations between relativistic species, one of which then undergoes
a temporary downward variation in its equation of state and generates
superhorizon-scale density fluctuations. Isocurvature decaying dark matter
models (iDDM) provide concrete examples. This mechanism solves the
phenomenological problems of traditional isocurvature models, allowing iDDM
models to fit the current CMB and large-scale structure data, while still
providing novel behavior. We characterize the decaying dark matter and its
decay products as a single component of ``generalized dark matter''. This
simplifies calculations in decaying dark matter models and others that utilize
this mechanism for structure formation.Comment: 4 pages, 3 figures, submitted to PRD (rapid communications
Inversive Meadows and Divisive Meadows
Inversive meadows are commutative rings with a multiplicative identity
element and a total multiplicative inverse operation whose value at 0 is 0.
Divisive meadows are inversive meadows with the multiplicative inverse
operation replaced by a division operation. We give finite equational
specifications of the class of all inversive meadows and the class of all
divisive meadows. It depends on the angle from which they are viewed whether
inversive meadows or divisive meadows must be considered more basic. We show
that inversive and divisive meadows of rational numbers can be obtained as
initial algebras of finite equational specifications. In the spirit of
Peacock's arithmetical algebra, we study variants of inversive and divisive
meadows without an additive identity element and/or an additive inverse
operation. We propose simple constructions of variants of inversive and
divisive meadows with a partial multiplicative inverse or division operation
from inversive and divisive meadows. Divisive meadows are more basic if these
variants are considered as well. We give a simple account of how mathematicians
deal with 1 / 0, in which meadows and a customary convention among
mathematicians play prominent parts, and we make plausible that a convincing
account, starting from the popular computer science viewpoint that 1 / 0 is
undefined, by means of some logic of partial functions is not attainable.Comment: 18 pages; error corrected; 29 pages, combined with arXiv:0909.2088
[math.RA] and arXiv:0909.5271 [math.RA
Three-Point Correlations in Weak Lensing Surveys: Model Predictions and Applications
We use the halo model of clustering to compute two- and three-point
correlation functions for weak lensing, and apply them in a new statistical
technique to measure properties of massive halos. We present analytical results
on the eight shear three-point correlation functions constructed using
combination of the two shear components at each vertex of a triangle. We
compare the amplitude and configuration dependence of the functions with
ray-tracing simulations and find excellent agreement for different scales and
models. These results are promising, since shear statistics are easier to
measure than the convergence. In addition, the symmetry properties of the shear
three-point functions provide a new and precise way of disentangling the
lensing E-mode from the B-mode due to possible systematic errors.
We develop an approach based on correlation functions to measure the
properties of galaxy-group and cluster halos from lensing surveys. Shear
correlations on small scales arise from the lensing matter within halos of mass
M > 10^13 solar masses. Thus the measurement of two- and three-point
correlations can be used to extract information on halo density profiles,
primarily the inner slope and halo concentration. We demonstrate the
feasibility of such an analysis for forthcoming surveys. We include covariances
in the correlation functions due to sample variance and intrinsic ellipticity
noise to show that 10% accuracy on profile parameters is achievable with
surveys like the CFHT Legacy survey, and significantly better with future
surveys. Our statistical approach is complementary to the standard approach of
identifying individual objects in survey data and measuring their properties.Comment: 30 pages, 21 figures. Corrected typos in equations (23) and (28).
Matches version for publication in MNRA
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