95 research outputs found
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
Cosmology with Phase 1 of the Square Kilometre Array Red Book 2018: Technical specifications and performance forecasts
We present a detailed overview of the cosmological surveys that we aim to carry out with Phase 1 of the Square Kilometre Array (SKA1) and the science that they will enable. We highlight three main surveys: a medium-deep continuum weak lensing and low-redshift spectroscopic HI galaxy survey over 5 000 deg2; a wide and deep continuum galaxy and HI intensity mapping (IM) survey over 20 000 deg2 from to 3; and a deep, high-redshift HI IM survey over 100 deg2 from to 6. Taken together, these surveys will achieve an array of important scientific goals: measuring the equation of state of dark energy out to with percent-level precision measurements of the cosmic expansion rate; constraining possible deviations from General Relativity on cosmological scales by measuring the growth rate of structure through multiple independent methods; mapping the structure of the Universe on the largest accessible scales, thus constraining fundamental properties such as isotropy, homogeneity, and non-Gaussianity; and measuring the HI density and bias out to . These surveys will also provide highly complementary clustering and weak lensing measurements that have independent systematic uncertainties to those of optical and near-infrared (NIR) surveys like Euclid, LSST, and WFIRST leading to a multitude of synergies that can improve constraints significantly beyond what optical or radio surveys can achieve on their own. This document, the 2018 Red Book, provides reference technical specifications, cosmological parameter forecasts, and an overview of relevant systematic effects for the three key surveys and will be regularly updated by the Cosmology Science Working Group in the run up to start of operations and the Key Science Programme of SKA1
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 ∼75 ± 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
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
Mass variance from archival X-ray properties of dark energy survey year-1 galaxy clusters
For abstract see published article
Relationship between germination and bell pepper seed structure assessed by the X-ray test
Brown bear attacks on humans : a worldwide perspective
The increasing trend of large carnivore attacks on humans not only raises human safety concerns but may also undermine large carnivore conservation efforts. Although rare, attacks by brown bears Ursus arctos are also on the rise and, although several studies have addressed this issue at local scales, information is lacking on a worldwide scale. Here, we investigated brown bear attacks (n = 664) on humans between 2000 and 2015 across most of the range inhabited by the species: North America (n = 183), Europe (n = 291), and East (n = 190). When the attacks occurred, half of the people were engaged in leisure activities and the main scenario was an encounter with a female with cubs. Attacks have increased significantly over time and were more frequent at high bear and low human population densities. There was no significant difference in the number of attacks between continents or between countries with different hunting practices. Understanding global patterns of bear attacks can help reduce dangerous encounters and, consequently, is crucial for informing wildlife managers and the public about appropriate measures to reduce this kind of conflicts in bear country.Peer reviewe
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