We investigate the form and evolution of the X-ray luminosity-temperature (L
X-kT) relation of a sample of 114 galaxy clusters observed with Chandra at 0.1 < z < 1.3. The clusters were divided into ...subsamples based on their X-ray morphology or whether they host strong cool cores. We find that when the core regions are excluded, the most relaxed clusters (or those with the strongest cool cores) follow an L
X-kT relation with a slope that agrees well with simple self-similar expectations. This is supported by an analysis of the gas density profiles of the systems, which shows self-similar behaviour of the gas profiles of the relaxed clusters outside the core regions. By comparing our data with clusters in the Representative XMM-Newton Cluster Structure Survey (REXCESS) sample, which extends to lower masses, we find evidence that the self-similar behaviour of even the most relaxed clusters breaks at around 3.5 keV. By contrast, the L
X-kT slopes of the subsamples of unrelaxed systems (or those without strong cool cores) are significantly steeper than the self-similar model, with lower mass systems appearing less luminous and higher mass systems appearing more luminous than the self-similar relation. We argue that these results are consistent with a model of non-gravitational energy input in clusters that combines central heating with entropy enhancements from merger shocks. Such enhancements could extend the impact of central energy input to larger radii in unrelaxed clusters, as suggested by our data. We also examine the evolution of the L
X-kT relation, and find that while the data appear inconsistent with simple self-similar evolution, the differences can be plausibly explained by selection bias, and thus we find no reason to rule out self-similar evolution. We show that the fraction of cool core clusters in our (non-representative) sample decreases at z > 0.5 and discuss the effect of this on measurements of the evolution in the L
X-kT relation.
We present Chandra observations of 23 galaxy groups and low-mass galaxy clusters at 0.03 < z < 0.15 with a median temperature of
${\sim }2{{\rm keV}}$
. The sample is a statistically complete ...flux-limited subset of the 400 deg2 survey. We investigated the scaling relation between X-ray luminosity (L) and temperature (T), taking selection biases fully into account. The logarithmic slope of the bolometric L–T relation was found to be 3.29 ± 0.33, consistent with values typically found for samples of more massive clusters. In combination with other recent studies of the L–T relation, we show that there is no evidence for the slope, normalization, or scatter of the L–T relation of galaxy groups being different than that of massive clusters. The exception to this is that in the special case of the most relaxed systems, the slope of the core-excised L–T relation appears to steepen from the self-similar value found for massive clusters to a steeper slope for the lower mass sample studied here. Thanks to our rigorous treatment of selection biases, these measurements provide a robust reference against which to compare predictions of models of the impact of feedback on the X-ray properties of galaxy groups.
The XXL Survey Pacaud, F; Clerc, N; Giles, P A ...
Astronomy and astrophysics (Berlin),
08/2016, Volume:
592
Journal Article
Peer reviewed
Open access
Context. The XXL Survey is the largest survey carried out by the XMM-Newton satellite and covers a total area of 50 square degrees distributed over two fields. It primarily aims at investigating the ...large-scale structures of the Universe using the distribution of galaxy clusters and active galactic nuclei as tracers of the matter distribution. The survey will ultimately uncover several hundreds of galaxy clusters out to a redshift of ~2 at a sensitivity of ~10 super(-14) ergs super(-1)cm super(-2) in the 0.5-2 keV band. Aims. This article presents the XXL bright cluster sample, a subsample of 100 galaxy clusters selected from the full XXL catalogue by setting a lower limit of 3 x 10 super(-14) erg s super(-1) cm super(-2) on the source flux within a 1? aperture. Methods. The selection function was estimated using a mixture of Monte Carlo simulations and analytical recipes that closely reproduce the source selection process. An extensive spectroscopic follow-up provided redshifts for 97 of the 100 clusters. We derived accurate X-ray parameters for all the sources. Scaling relations were self-consistently derived from the same sample in other publications of the series. On this basis, we study the number density, luminosity function, and spatial distribution of the sample. Results. The bright cluster sample consists of systems with masses between M sub(500)= 7 x 10 super(13) and 3 x 10 super(14)M sub(?), mostly located between z= 0.1 and 0.5. The observed sky density of clusters is slightly below the predictions from the WMAP9 model, and significantly below the prediction from the Planck 2015 cosmology. In general, within the current uncertainties of the cluster mass calibration, models with higher values of sigma sub(8) and/or Omega sub(M) appear more difficult to accommodate. We provide tight constraints on the cluster differential luminosity function and find no hint of evolution out to z~ 1. We also find strong evidence for the presence of large-scale structures in the XXL bright cluster sample and identify five new superclusters.
In this paper, we compute the expected number of vehicles with at least one two-hop path to a fixed roadside unit (RSU) in a multi-hop, one-dimensional vehicular ad hoc network (VANET) where other ...cars can act as relays. The pairwise channels experience Rayleigh fading in the random connection model, and so exist, with probability function of the mutual distance between the cars, or between the cars and the RSU. We derive exact equivalents for the expected number of cars with a two-hop connection to the RSU when the car density <inline-formula><tex-math notation="LaTeX">\rho</tex-math></inline-formula> tends to zero and infinity, and determine its behaviour using an infinite oscillating power series in <inline-formula><tex-math notation="LaTeX">\rho</tex-math></inline-formula>, which is accurate for all regimes. We also corroborate those findings to a realistic situation, using snapshots of actual traffic data. Finally, a normal approximation is discussed for the probability mass function of the number of cars with a two-hop connection to the RSU.
Objective
To investigate whether rituximab, an anti–B cell therapy, improves symptoms of fatigue and oral dryness in patients with primary Sjögren's syndrome (SS).
Methods
We conducted a multicenter, ...randomized, double‐blind, placebo‐controlled, parallel‐group trial that included health economic analysis. Anti‐Ro–positive patients with primary SS, symptomatic fatigue, and oral dryness were recruited from 25 UK rheumatology clinics from August 2011 to January 2014. Patients were centrally randomized to receive either intravenous (IV) placebo (250 ml saline) or IV rituximab (1,000 mg in 250 ml saline) in 2 courses at weeks 0, 2, 24, and 26, with pre‐ and postinfusion medication including corticosteroids. The primary end point was the proportion of patients achieving a 30% reduction in either fatigue or oral dryness at 48 weeks, as measured by visual analog scale. Other outcome measures included salivary and lacrimal flow rates, quality of life, scores on the European League Against Rheumatism (EULAR) Sjögren's Syndrome Patient Reported Index and EULAR Sjögren's Syndrome Disease Activity Index, symptoms of ocular and overall dryness, pain, globally assessed disease activity, and cost‐effectiveness.
Results
All 133 patients who were randomized to receive placebo (n = 66) or rituximab (n = 67) were included in the primary analysis. Among patients with complete data, 21 of 56 placebo‐treated patients and 24 of 61 rituximab‐treated patients achieved the primary end point. After multiple imputation of missing outcomes, response rates in the placebo and rituximab groups were 36.8% and 39.8%, respectively (adjusted odds ratio 1.13 95% confidence interval 0.50, 2.55). There were no significant improvements in any outcome measure except for unstimulated salivary flow. The mean ± SD costs per patient for rituximab and placebo were £10,752 ± 264.75 and £2,672 ± 241.71, respectively. There were slightly more adverse events (AEs) reported in total for rituximab, but there was no difference in serious AEs (10 in each group).
Conclusion
The results of this study indicate that rituximab is neither clinically effective nor cost‐effective in this patient population.
The XXL Survey Pacaud, F.; Pierre, M.; Melin, J.-B. ...
Astronomy and astrophysics (Berlin),
12/2018, Volume:
620
Journal Article
Peer reviewed
Open access
Context.
We present an estimation of cosmological parameters with clusters of galaxies.
Aims.
We constrain the Ω
m
,
σ
8
, and
w
parameters from a stand-alone sample of X-ray clusters detected in the ...50 deg
2
XMM-XXL survey with a well-defined selection function.
Methods.
We analyse the redshift distribution of a sample comprising 178 high signal-to-noise ratio clusters out to a redshift of unity. The cluster sample scaling relations are determined in a self-consistent manner.
Results.
In a lambda cold dark matter (ΛCDM) model, the cosmology favoured by the XXL clusters compares well with results derived from the
Planck
Sunyaev-Zel’dovich clusters for a totally different sample (mass/redshift range, selection biases, and scaling relations). However, with this preliminary sample and current mass calibration uncertainty, we find no inconsistency with the
Planck
CMB cosmology. If we relax the
w
parameter, the
Planck
CMB uncertainties increase by a factor of ~10 and become comparable with those from XXL clusters. Combining the two probes allows us to put constraints on Ω
m
= 0.316 ± 0.060,
σ
8
= 0.814 ± 0.054, and
w
= −1.02 ± 0.20.
Conclusions.
This first self-consistent cosmological analysis of a sample of serendipitous XMM clusters already provides interesting insights into the constraining power of the XXL survey. Subsequent analysis will use a larger sample extending to lower confidence detections and include additional observable information, potentially improving posterior uncertainties by roughly a factor of 3.
The XXL Survey Giles, P A; Maughan, B J; Pacaud, F ...
Astronomy and astrophysics (Berlin),
08/2016, Volume:
592
Journal Article
Peer reviewed
Open access
Context. The XXL Survey is the largest homogeneous survey carried out with XMM-Newton. Covering an area of 50 deg super(2), the survey contains several hundred galaxy clusters out to a redshift of ~2 ...above an X-ray flux limit of ~5 x 10 super(-15) erg cm super(-2) s super(-1). This paper belongs to the first series of XXL papers focusing on the bright cluster sample. Aims. We investigate the luminosity-temperature (LT) relation for the brightest clusters detected in the XXL Survey, taking fully into account the selection biases. We investigate the form of the LT relation, placing constraints on its evolution. Methods. We have classified the 100 brightest clusters in the XXL Survey based on their measured X-ray flux. These 100 clusters have been analysed to determine their luminosity and temperature to evaluate the LT relation. We used three methods to fit the form of the LT relation, with two of these methods providing a prescription to fully take into account the selection effects of the survey. We measure the evolution of the LT relation internally using the broad redshift range of the sample. Results. Taking fully into account selection effects, we find a slope of the bolometric LT relation of B sub(LT)= 3.08 + or - 0.15, steeper than the self-similar expectation (B sub(LT)= 2). Our best-fit result for the evolution factor is E(z) super(1.64 + or - 0.77), fully consistent with "strong self-similar" evolution where clusters scale self-similarly with both mass and redshift. However, this result is marginally stronger than "weak self-similar" evolution, where clusters scale with redshift alone. We investigate the sensitivity of our results to the assumptions made in our fitting model, finding that using an external LT relation as a low-z baseline can have a profound effect on the measured evolution. However, more clusters are needed in order to break the degeneracy between the choice of likelihood model and mass-temperature relation on the derived evolution.
In this perspective, we introduce recent research into the structure and function of complex investor networks supporting sustainability efforts. Using the case of solar, wind and hydro energy ...technologies, this perspective explores the complexity in low-carbon finance markets, defined as markets that direct capital flows towards low-carbon technologies, using network approaches to study their structure and dynamics. Investors are modeled as nodes which form a network or higher-order network connected by edges representing projects in which joint funding or security-related insurance was provided or other investment-related interaction occurred. We review the literature on investor networks generally, particularly in the case of complex networks, and address areas where these ideas were applied in this emerging field. The complex investor dynamics which emerge from the extant funding scenarios are not well understood. These dynamics have the potential to result in interesting non-linear behaviour, growth, and decline, which can be studied, explained and controlled using the tools of network science.
We present the results of work involving a statistically complete sample of 34 galaxy clusters, in the redshift range 0.15 = z = 0.3 observed with Chandra. We investigate the luminosity-mass (LM) ...relation for the cluster sample, with the masses obtained via a full hydrostatic mass analysis. We utilize a method to fully account for selection biases when modelling the LM relation, and find that the LM relation is significantly different from the relation modelled when not account for selection effects. We find that the luminosity of our clusters is 2.2 plus or minus 0.4 times higher (when accounting for selection effects) than the average for a given mass and its mass is 30 per cent lower than the population average for a given luminosity. Equivalently, using the LM relation measured from this sample without correcting for selection biases would lead to the underestimation by 40 percent of the average mass of a cluster with a given luminosity. Comparing the hydrostatic masses to mass estimates determined from the YX parameter, we find that they are entirely consistent, irrespective of the dynamical state of the cluster.
The XXL Survey Lieu, M; Smith, G P; Giles, P A ...
Astronomy and astrophysics (Berlin),
08/2016, Volume:
592
Journal Article
Peer reviewed
Open access
Context. The XXL Survey is the largest survey carried out by XMM-Newton. Covering an area of 50 deg super(2), the survey contains ~450 galaxy clusters out to a redshift ~2 and to an X-ray flux limit ...of ~ 5 x 10 super(-15) erg s super(-1) cm super(-2). This paper is part of the first release of XXL results focussed on the bright cluster sample. Aims. We investigate the scaling relation between weak-lensing mass and X-ray temperature for the brightest clusters in XXL. The scaling relation discussed in this article is used to estimate the mass of all 100 clusters in XXL-100-GC. Methods. Based on a subsample of 38 objects that lie within the intersection of the northern XXL field and the publicly available CFHTLenS shear catalog, we derive the weak-lensing mass of each system with careful considerations of the systematics. The clusters lie at 0.1 <z< 0.6 and span a temperature range of T? 1?5 keV. We combine our sample with an additional 58 clusters from the literature, increasing the range to T? 1?10 keV. To date, this is the largest sample of clusters with weak-lensing mass measurements that has been used to study the mass-temperature relation. Results. The mass-temperature relation fit (M? Tb) to the XXL clusters returns a slope b= 1.78 super(+0.37) sub(-0.32) and intrinsic scatter sigma sub(ln)MT? 0.53; the scatter is dominated by disturbed clusters. The fit to the combined sample of 96 clusters is in tension with self-similarity, b= 1.67 + or - 0.12 and sigma sub(ln)MT? 0.41. Conclusions. Overall our results demonstrate the feasibility of ground-based weak-lensing scaling relation studies down to cool systems of ~1 keV temperature and highlight that the current data and samples are a limit to our statistical precision. As such we are unable to determine whether the validity of hydrostatic equilibrium is a function of halo mass. An enlarged sample of cool systems, deeper weak-lensing data, and robust modelling of the selection function will help to explore these issues further.
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