75 research outputs found
Environmental dependence of X-ray and optical properties of galaxy clusters
Galaxy clusters are widely used to constrain cosmological parameters through their properties, such as masses, luminosity, and temperature distributions. One should take into account all kind of biases that could affect these analyses in order to obtain reliable constraints. In this work, we study the difference in the properties of clusters residing in different large-scale environments, defined by their position within or outside of voids, and the density of their surrounding space. We use both observational and simulation cluster and void catalogues, i.e. XMM Cluster Survey (XCS) and redMaPPer clusters, Baryon Oscillation Spectroscopic Survey (BOSS) voids, and Magneticum simulations. We devise two different environmental proxies for the clusters and study their redshift, richness, mass, X-ray luminosity, and temperature distributions, as well as some properties of their galaxy populations. We use the KolmogorovâSmirnov two-sample test to discover that richer and more massive clusters are more prevalent in overdense regions and outside of voids. We also find that clusters of matched richness and mass in overdense regions and outside voids tend to have higher X-ray luminosities and temperatures. These differences could have important implications for precision cosmology with clusters of galaxies, since cluster mass calibrations can vary with environment
The XMM Cluster Survey: Evidence for energy injection at high redshift from evolution of the X-ray luminosity-temperature relation
We measure the evolution of the X-ray luminosity-temperature (L_X-T) relation
since z~1.5 using a sample of 211 serendipitously detected galaxy clusters with
spectroscopic redshifts drawn from the XMM Cluster Survey first data release
(XCS-DR1). This is the first study spanning this redshift range using a single,
large, homogeneous cluster sample. Using an orthogonal regression technique, we
find no evidence for evolution in the slope or intrinsic scatter of the
relation since z~1.5, finding both to be consistent with previous measurements
at z~0.1. However, the normalisation is seen to evolve negatively with respect
to the self-similar expectation: we find E(z)^{-1} L_X = 10^{44.67 +/- 0.09}
(T/5)^{3.04 +/- 0.16} (1+z)^{-1.5 +/- 0.5}, which is within 2 sigma of the zero
evolution case. We see milder, but still negative, evolution with respect to
self-similar when using a bisector regression technique. We compare our results
to numerical simulations, where we fit simulated cluster samples using the same
methods used on the XCS data. Our data favour models in which the majority of
the excess entropy required to explain the slope of the L_X-T relation is
injected at high redshift. Simulations in which AGN feedback is implemented
using prescriptions from current semi-analytic galaxy formation models predict
positive evolution of the normalisation, and differ from our data at more than
5 sigma. This suggests that more efficient feedback at high redshift may be
needed in these models.Comment: Accepted for publication in MNRAS; 12 pages, 6 figures; added
references to match published versio
Synergy between the Large Synoptic Survey Telescope and the Square Kilometre Array
We provide an overview of the science benefits of combining information from the Square Kilometre Array (SKA) and the Large Synoptic Survey Telescope (LSST). We first summarise the capabilities and timeline of the LSST and overview its science goals. We then discuss the science questions in common between the two projects, and how they can be best addressed by combining the data from both telescopes. We describe how weak gravitational lensing and galaxy clustering studies with LSST and SKA can provide improved constraints on the causes of the cosmological acceleration. We summarise the benefits to galaxy evolution studies of combining deep optical multi-band imaging with radio observations. Finally, we discuss the excellent match between one of the most unique features of the LSST, its temporal cadence in the optical waveband, and the time resolution of the SKA
Populations behind the source-subtracted cosmic infrared background anisotropies
While the upcoming telescopes will reveal correspondingly fainter, more
distant galaxies, a question will persist: what more is there that these
telescopes cannot see? One answer is the source-subtracted Cosmic Infrared
Background (CIB). The CIB is comprised of the collective light from all sources
remaining after known, resolved sources are accounted for. Ever-more-sensitive
surveys will identify the brightest of these, allowing them to be removed, and
- like peeling layers off an onion - reveal deeper layers of the CIB. In this
way it is possible to measure the contributions from populations not accessible
to direct telescopic observation. Measurement of fluctuations in the
source-subtracted CIB, i.e., the spatial power spectrum of the CIB after
subtracting resolved sources, provides a robust means of characterizing its
faint, and potentially new, populations. Studies over the past 15 years have
revealed source-subtracted CIB fluctuations on scales out to ~100' which cannot
be explained by extrapolating from known galaxy populations. Moreover, they
appear highly coherent with the unresolved Cosmic X-ray Background, hinting at
a significant population of accreting black holes among the CIB sources.
Characterizing the source-subtracted CIB with high accuracy, and thereby
constraining the nature of the new populations, is feasible with upcoming
instruments and would produce critically important cosmological information in
the next decade. New coextensive deep and wide-area near-infrared, X-ray, and
microwave surveys will bring decisive opportunities to examine, with high
fidelity, the spatial spectrum and origin of the CIB fluctuations and their
cross-correlations with cosmic microwave and X-ray backgrounds, and determine
the formation epochs and the nature of the new sources (stellar nucleosynthetic
or accreting black holes).Comment: Science whitepaper submitted to the Astro2020 Decadal Surve
Scalar phantom energy as a cosmological dynamical system
Phantom energy can be visualized as a scalar field with a (non-canonical)
negative kinetic energy term. We use the dynamical system formalism to study
the attractor behavior of a cosmological model containing a phantom scalar
field endowed with an exponential potential of the form , and a perfect fluid with constant equation of
state ; the latter can be of the phantom type too. As in the canonical
case, three characteristic solutions can be identified. The scaling solution
exists but is either unstable or of no physical interest. Thus, there are only
two stable critical points which are of physical interest, corresponding to the
perfect fluid and scalar field dominated solutions, respectively. The most
interesting case arises for , which allows the
coexistence of the three solutions. The main features of each solution are
discussed in turn.Comment: 6 pages, 3 eps figures; uses RevTex4. New references added, and
changes made according to referee's suggestions. Matches published version in
JCA
The Accelerated Acceleration of the Universe
We present a simple mechanism which can mimic dark energy with an equation of
state w < -1 as deduced from the supernova data. We imagine that the universe
is accelerating under the control of a quintessence field, which is moving up a
very gently sloping potential. As a result, the potential energy and hence the
acceleration increases at lower redshifts. Fitting this behavior with a dark
energy model with constant w would require w<-1. In fact we find that the
choice of parameters which improves the fit to the SNe mimics w = -1.4 at low
redshifts. Running up the potential in fact provides the best fit to the SN
data for a generic quintessence model. However, unlike models with phantoms,
our model does not have negative energies or negative norm states. Future
searches for supernovae at low redshifts 0.1 < z < 0.5 and at high redshifts
z>1 may be a useful probe of our proposal.Comment: 14 pages, 5 figure
For whom is a health-promoting intervention effective? Predictive factors for performing activities of daily living independently
BACKGROUND: Health-promoting interventions tailored to support older persons to remain in their homes, so-called "ageing in place" is important for supporting or improving their health. The health-promoting programme "Elderly Persons in the Risk Zone," (EPRZ) was set up for this purpose and has shown positive results for maintaining independence in activities of daily living for older persons 80 years and above at 1- and 2 year follow-ups. The aim of this study was to explore factors for maintaining independence in the EPRZ health-promoting programme.METHODS: Total of 459 participants in the original trial was included in the analysis; 345 in the programme arm and 114 in the control arm. Thirteen variables, including demographic, health, and programme-specific indicators, were chosen as predictors for independence of activities of daily living. Logistic regression was performed separately for participants in the health promotion programme and in the control arm.RESULTS: In the programme arm, being younger, living alone and self-rated lack of tiredness in performing mobility activities predicted a positive effect of independence in activities of daily living at 1-year follow-up (odds ratio [OR] 1.18, 1.73, 3.02) and 2-year, (OR 1.13, 2.01, 2.02). In the control arm, being less frail was the only predictor at 1-year follow up (OR 1.6 1.09, 2.4); no variables predicted the outcome at the 2-year follow-up.CONCLUSIONS: Older persons living alone - as a risk of ill health - should be especially recognized and offered an opportunity to participate in health-promoting programmes such as "Elderly Persons in the Risk Zone". Further, screening for subjective frailty could form an advantageous guiding principle to target the right population when deciding to whom health-promoting intervention should be offered.TRIAL REGISTRATION: The original clinical trial was registered at ClinicalTrials.gov. Identifier: NCT00877058 , April 6, 2009
Imprint of DES superstructures on the cosmic microwave background
Small temperature anisotropies in the cosmic microwave background (CMB) can be sourced by density perturbations via the late-time integrated Sachs-Wolfe (ISW) effect. Large voids and superclusters are excellent environments to make a localized measurement of this tiny imprint. In some cases excess signals have been reported. We probed these claims with an independent data set, using the first year data of the Dark Energy Survey (DES) in a different footprint, and using a different superstructure finding strategy. We identified 52 large voids and 102 superclusters at redshifts 0.2 < z < 0.65. We used the Jubilee simulation to a priori evaluate the optimal ISW measurement configuration for our compensated top-hat filtering technique, and then performed a stacking measurement of the CMB temperature field based on the DES data. For optimal configurations, we detected a cumulative cold imprint of voids with DeltaTf â -5.0 ± 3.7 muK and a hot imprint of superclusters DeltaTf â 5.1 ± 3.2 muK; this is Ë1.2sigma higher than the expected |DeltaTf| â 0.6 muK imprint of such superstructures in Lambda cold dark matter (LambdaCDM). If we instead use an a posteriori selected filter size (R/Rv = 0.6), we can find a temperature decrement as large as DeltaTf â -9.8 ± 4.7 muK for voids, which is Ë2sigma above LambdaCDM expectations and is comparable to previous measurements made using Sloan Digital Sky Survey superstructure data
Dark Energy Surveyed Year 1 results: calibration of cluster mis-centring in the redMaPPer catalogues
The centre determination of a galaxy cluster from an optical cluster finding algorithm can be offset from theoretical prescriptions or N-body definitions of its host halo centre. These offsets impact the recovered cluster statistics, affecting both richness measurements and the weak lensing shear profile around the clusters. This paper models the centring performance of the redMaPPer cluster finding algorithm using archival X-ray observations of redMaPPer selected clusters. Assuming the X-ray emission peaks as the fiducial halo centres, and through analysing their offsets to the redMaPPer centres, we find that âŒ75 ± 8 per cent of the redMaPPer clusters are well centred and the mis-centred offset follows a Gamma distribution in normalized, projected distance. These mis-centring offsets cause a systematic underestimation of cluster richness relative to the well-centred clusters, for which we propose a descriptive model. Our results enable the DES Y1 cluster cosmology analysis by characterizing the necessary corrections to both the weak lensing and richness abundance functions of the DES Y1 redMaPPer cluster catalogue
Stellar mass as a galaxy cluster mass proxy: application to the Dark Energy Survey redMaPPer clusters
We introduce a galaxy cluster mass observable, ÎŒâ, based on the stellar masses of cluster members, and we present results for the Dark Energy Survey (DES) Year 1 (Y1) observations. Stellar masses are computed using a Bayesian model averaging method, and are validated for DES data using simulations and COSMOS data. We show that ÎŒâ works as a promising mass proxy by comparing our predictions to X-ray measurements. We measure the X-ray temperatureâÎŒ_{â} relation for a total of 129 clusters matched between the wide-field DES Y1 redMaPPer catalogue and Chandra and XMM archival observations, spanning the redshift range 0.1 < z < 0.7. For a scaling relation that is linear in logarithmic space, we find a slope of α = 0.488 ± 0.043 and a scatter in the X-ray temperature at fixed ÎŒ_{*} of Ï1nT_{x}|ÎŒ_{*} = 0.266_{-0.020}^{+0.019} for the joint sample. By using the halo mass scaling relations of the X-ray temperature from the Weighing the Giants program, we further derive the ÎŒâ-conditioned scatter in mass, finding Ï1nM|ÎŒ_{*} = 0.26_{-0.10}^{+0.15}. These results are competitive with well-established cluster mass proxies used for cosmological analyses, showing that ÎŒ_{â} can be used as a reliable and physically motivated mass proxy to derive cosmological constraints
- âŠ