Context. Measuring and calibrating relations between cluster observables is critical for resource-limited studies. The mass–richness relation of clusters offers an observationally inexpensive way of ...estimating masses. Its calibration is essential for cluster and cosmological studies, especially for high-redshift clusters. Weak gravitational lensing magnification is a promising and complementary method to shear studies, that can be applied at higher redshifts. Aims. We aim to employ the weak lensing magnification method to calibrate the mass–richness relation up to a redshift of 1.4. We used the Spitzer Adaptation of the Red-Sequence Cluster Survey (SpARCS) galaxy cluster candidates (0.2 < z < 1.4) and optical data from the Canada France Hawaii Telescope (CFHT) to test whether magnification can be effectively used to constrain the mass of high-redshift clusters. Methods. Lyman-break galaxies (LBGs) selected using the u-band dropout technique and their colours were used as a background sample of sources. LBG positions were cross-correlated with the centres of the sample of SpARCS clusters to estimate the magnification signal, which was optimally-weighted using an externally-calibrated LBG luminosity function. The signal was measured for cluster sub-samples, binned in both redshift and richness. Results. We measured the cross-correlation between the positions of galaxy cluster candidates and LBGs and detected a weak lensing magnification signal for all bins at a detection significance of 2.6–5.5σ. In particular, the significance of the measurement for clusters with z> 1.0 is 4.1σ; for the entire cluster sample we obtained an average M200 of 1.28 -0.21+0.23 × 1014 M⊙. Conclusions. Our measurements demonstrated the feasibility of using weak lensing magnification as a viable tool for determining the average halo masses for samples of high redshift galaxy clusters. The results also established the success of using galaxy over-densities to select massive clusters at z > 1. Additional studies are necessary for further modelling of the various systematic effects we discussed.
Aims.Several photometric redshift (photo-z) codes are discussed in the literature and some are publicly available to be used by the community. We analyse the relative performance of different codes ...in blind applications to ground-based data. In particular, we study how the choice of the code-template combination, the depth of the data, and the filter set influences the photo-z accuracy. Methods.We performed a blind test of different photo-z codes on imaging datasets with different depths and filter coverages and compared the results to large spectroscopic catalogues. We analysed the photo-z error behaviour to select cleaner subsamples with more secure photo-z estimates. We consider Hyperz, BPZ, and the code used in the CADIS, COMBO-17, and HIROCS surveys. Results. The photo-z error estimates of the three codes do not correlate tightly with the accuracy of the photo-z's. While very large errors sometimes indicate a true catastrophic photo-z failure, smaller errors are usually not meaningful. For any given dataset, we find significant differences in redshift accuracy and outlier rates between the different codes when compared to spectroscopic redshifts. However, different codes excel in different regimes. The agreement between different sets of photo-z's is better for the subsample with secure spectroscopic redshifts than for the whole catalogue. Outlier rates in the latter are typically larger by at least a factor of two. Conclusions. Running today's photo-z codes on well-calibrated ground-based data can lead to reasonable accuracy. The actual performance on a given dataset is largely dependent on the template choice and on realistic instrumental response curves. The photo-z error estimation of today's codes from the probability density function is not reliable, and reported errors do not correlate tightly with accuracy. It would be desirable to improve this aspect for future applications so as to get a better handle on rejecting objects with grossly inaccurate photo-z's. The secure spectroscopic subsamples commonly used for assessments of photo-z accuracy may be biased toward objects for which the photo-z's are easier to estimate than for a complete flux-limited sample, resulting in very optimistic estimates.
Evidence shows that prolonged sitting is associated with an increased risk of mortality, independent of physical activity (PA). The aim of the study was to identify correlates of sedentary time (ST) ...in different age groups and day types (i.e. school-/work day versus non-school-/non-work day).
The study sample consisted of 1895 Dutch children (4-11 years), 1131 adolescents (12-17 years), 8003 adults (18-64 years) and 1569 elderly (65 years and older) who enrolled in the Dutch continuous national survey 'Injuries and Physical Activity in the Netherlands' between 2006 and 2011. Respondents estimated the number of sitting hours during a regular school-/workday and a regular non-school/non-work day. Multiple linear regression analyses on cross-sectional data were used to identify correlates of ST.
Significant positive associations with ST were observed for: higher age (4-to-17-year-olds and elderly), male gender (adults), overweight (children), higher education (adults ≥ 30 years), urban environment (adults), chronic disease (adults ≥ 30 years), sedentary work (adults), not meeting the moderate to vigorous PA (MVPA) guideline (children and adults ≥ 30 years) and not meeting the vigorous PA (VPA) guideline (4-to-17-year-olds). Correlates of ST that significantly differed between day types were working hours and meeting the VPA guideline. More working hours were associated with more ST on school-/work days. In children and adolescents, meeting the VPA guideline was associated with less ST on non-school/non-working days only.
This study provides new insights in the correlates of ST in different age groups and thus possibilities for interventions in these groups. Correlates of ST appear to differ between age groups and to a lesser degree between day types. This implies that interventions to reduce ST should be age specific. Longitudinal studies are needed to draw conclusions on causality of the relationship between identified correlates and ST.
We study the correlations of the shear signal between triplets of sources in the Canada–France–Hawaii Telescope Lensing Survey (CFHTLenS) to probe cosmological parameters via the matter bispectrum. ...In contrast to previous studies, we adopt a non-Gaussian model of the data likelihood which is supported by our simulations of the survey. We find that for state-of-the-art surveys, similar to CFHTLenS, a Gaussian likelihood analysis is a reasonable approximation, albeit small differences in the parameter constraints are already visible. For future surveys we expect that a Gaussian model becomes inaccurate. Our algorithm for a refined non-Gaussian analysis and data compression is then of great utility especially because it is not much more elaborate if simulated data are available. Applying this algorithm to the third-order correlations of shear alone in a blind analysis, we find a good agreement with the standard cosmological model:
$\Sigma _8=\sigma _8(\Omega _{\rm m}/0.27)^{0.64}=0.79^{+0.08}_{-0.11}$
for a flat Λ cold dark matter cosmology with h = 0.7 ± 0.04 (68 per cent credible interval). Nevertheless our models provide only moderately good fits as indicated by χ2/dof = 2.9, including a 20 per cent rms uncertainty in the predicted signal amplitude. The models cannot explain a signal drop on scales around 15 arcmin, which may be caused by systematics. It is unclear whether the discrepancy can be fully explained by residual point spread function systematics of which we find evidence at least on scales of a few arcmin. Therefore we need a better understanding of higher order correlations of cosmic shear and their systematics to confidently apply them as cosmological probes.
Aims. We identify and study a previously unknown systematic effect on cosmic shear measurements, caused by the selection of galaxies used for shape measurement, in particular the rejection of close ...(blended) galaxy pairs. Methods. We use ray-tracing simulations based on the Millennium Simulation and a semi-analytical model of galaxy formation to create realistic galaxy catalogues. From these, we quantify the bias in the shear correlation functions by comparing measurements made from galaxy catalogues with and without removal of close pairs. A likelihood analysis is used to quantify the resulting shift in estimates of cosmological parameters. Results. The filtering of objects with close neighbours: (a) changes the redshift distribution of the galaxies used for correlation function measurements; and (b) correlates the number density of sources in the background with the density field in the foreground. This leads to a scale-dependent bias of the correlation function of several percent, translating into biases of cosmological parameters of similar amplitude. This makes this new systematic effect potentially harmful for upcoming and planned cosmic shear surveys. As a remedy, we propose and test a weighting scheme that can significantly reduce the bias.
To critically review the literature with respect to the effectiveness of worksite physical activity programs on physical activity, physical fitness, and health.
A search for relevant English-written ...papers published between 1980 and 2000 was conducted using MEDLINE, EMBASE, Sportdiscus, CINAHL, and Psychlit. The key words used involved a combination of concepts regarding type of study, study population, intervention, and outcome measure. In addition, a search was performed in our personal databases, as well as a reference search of the studies retrieved.
The following criteria for inclusion were used: 1) randomized, controlled trial or nonrandomized, controlled trial; 2) working population; 3) worksite intervention program to promote employees' physical activity or physical fitness; and 4) physical activity, physical fitness, or health-related outcomes.
Two reviewers independently evaluated the quality of relevant studies using a predefined set of nine methodological criteria. Conclusions regarding the effectiveness of a worksite physical activity programs were based on a rating system consisting of five levels of evidence.
Fifteen randomized, controlled trials and 11 nonrandomized, controlled trials met the criteria for inclusion and were reviewed. Six randomized, controlled trials and none of the nonrandomized, controlled trials were of high methodological quality. Strong evidence was found for a positive effect of a worksite physical activity program on physical activity and musculoskeletal disorders. Limited evidence was found for a positive effect on fatigue. For physical fitness, general health, blood serum lipids, and blood pressure, inconclusive or no evidence was found for a positive effect.
To increase the level of physical activity and to reduce the risk of musculoskeletal disorders, we support implementation of worksite physical activity programs. For the other outcome measures, scientific evidence of the effectiveness of such a program is still limited or inconclusive, which is mainly the result of the small number of high-quality trials. Therefore, we recommend performing more randomized, controlled trials of high methodological quality, taking into account criteria such as randomization, blinding, and compliance.
ABSTRACT We use the GALFORM semi-analytical galaxy formation model implemented in the Planck Millennium N-body simulation to build a mock galaxy catalogue on an observer’s past lightcone. The mass ...resolution of this N-body simulation is almost an order of magnitude better than in previous simulations used for this purpose, allowing us to probe fainter galaxies and hence build a more complete mock catalogue at low redshifts. The high time cadence of the simulation outputs allows us to make improved calculations of galaxy properties and positions in the mock. We test the predictions of the mock against the Physics of the Accelerating Universe Survey, a narrow-band imaging survey with highly accurate and precise photometric redshifts, which probes the galaxy population over a lookback time of 8 billion years. We compare the model against the observed number counts, redshift distribution, and evolution of the observed colours and find good agreement; these statistics avoid the need for model-dependent processing of the observations. The model produces red and blue populations that have similar median colours to the observations. However, the bimodality of galaxy colours in the model is stronger than in the observations. This bimodality is reduced on including a simple model for errors in the GALFORM photometry. We examine how the model predictions for the observed galaxy colours change when perturbing key model parameters. This exercise shows that the median colours and relative abundance of red and blue galaxies provide constraints on the strength of the feedback driven by supernovae used in the model.
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