3,765 research outputs found
Comprehensive Two-Point Analyses of Weak Gravitational Lensing Surveys
We present a framework for analyzing weak gravitational lensing survey data,
including lensing and source-density observables, plus spectroscopic redshift
calibration data. All two-point observables are predicted in terms of
parameters of a perturbed Robertson-Walker metric, making the framework
independent of the models for gravity, dark energy, or galaxy properties. For
Gaussian fluctuations the 2-point model determines the survey likelihood
function and allows Fisher-matrix forecasting. The framework includes nuisance
terms for the major systematic errors: shear measurement errors, magnification
bias and redshift calibration errors, intrinsic galaxy alignments, and
inaccurate theoretical predictions. We propose flexible parameterizations of
the many nuisance parameters related to galaxy bias and intrinsic alignment.
For the first time we can integrate many different observables and systematic
errors into a single analysis. As a first application of this framework, we
demonstrate that: uncertainties in power-spectrum theory cause very minor
degradation to cosmological information content; nearly all useful information
(excepting baryon oscillations) is extracted with ~3 bins per decade of angular
scale; and the rate at which galaxy bias varies with redshift substantially
influences the strength of cosmological inference. The framework will permit
careful study of the interplay between numerous observables, systematic errors,
and spectroscopic calibration data for large weak-lensing surveys.Comment: submitted to Ap
Ecological knowledge, leadership, and the evolution of menopause in killer whales
This is the final version of the article. Available from Elsevier via the DOI in this record.There is another record in ORE for this publication: http://hdl.handle.net/10871/16488Classic life-history theory predicts that menopause should not occur because there should be no selection for survival after the cessation of reproduction [1]. Yet, human females routinely live 30 years after they have stopped reproducing [2]. Only two other species-killer whales (Orcinus orca) and short-finned pilot whales (Globicephala macrorhynchus) [3, 4]-have comparable postreproductive lifespans. In theory, menopause can evolve via inclusive fitness benefits [5, 6], but the mechanisms by which postreproductive females help their kin remain enigmatic. One hypothesis is that postreproductive females act as repositories of ecological knowledge and thereby buffer kin against environmental hardships [7, 8]. We provide the first test of this hypothesis using a unique long-term dataset on wild resident killer whales. We show three key results. First, postreproductively aged females lead groups during collective movement in salmon foraging grounds. Second, leadership by postreproductively aged females is especially prominent in difficult years when salmon abundance is low. This finding is critical because salmon abundance drives both mortality and reproductive success in resident killer whales [9, 10]. Third, females are more likely to lead their sons than they are to lead their daughters, supporting predictions of recent models [5] of the evolution of menopause based on kinship dynamics. Our results show that postreproductive females may boost the fitness of kin through the transfer of ecological knowledge. The value gained from the wisdom of elders can help explain why female resident killer whales and humans continue to live long after they have stopped reproducing.This research was funded by a Natural Environment Research Council grant (NE/K01286X/1) to D.P.C., D.W.F., and M.A.C
The Local Nanohertz Gravitational-Wave Landscape From Supermassive Black Hole Binaries
Supermassive black hole binaries (SMBHBs) in the 10 million to 10 billion
range form in galaxy mergers, and live in galactic nuclei with large
and poorly constrained concentrations of gas and stars. There are currently no
observations of merging SMBHBs--- it is in fact possible that they stall at
their final parsec of separation and never merge. While LIGO has detected high
frequency GWs, SMBHBs emit GWs in the nanohertz to millihertz band. This is
inaccessible to ground-based interferometers, but possible with Pulsar Timing
Arrays (PTAs). Using data from local galaxies in the 2 Micron All-Sky Survey,
together with galaxy merger rates from Illustris, we find that there are on
average sources emitting GWs in the PTA band, and binaries
which will never merge. Local unresolved SMBHBs can contribute to GW background
anisotropy at a level of , and if the GW background can be
successfully isolated, GWs from at least one local SMBHB can be detected in 10
years.Comment: submitted to Nature Astronomy (reformatted for arXiv
Neutrino mass bounds from cosmology
Cosmology is at present one of the most powerful probes of neutrino
properties. The advent of precision data from the cosmic microwave background
and large scale structure has allowed for a very strong bound on the neutrino
mass. Here, I review the status of cosmological bounds on neutrino properties
with emphasis on mass bounds on light neutrinos.Comment: 6 pages, 3 figures, talk given at NOW2004 workshop, Conca
Specchiulla, Italy, September 11-17, 200
Catastrophic photometric redshift errors: weak lensing survey requirements
We study the sensitivity of weak lensing surveys to the effects of
catastrophic redshift errors - cases where the true redshift is misestimated by
a significant amount. To compute the biases in cosmological parameters, we
adopt an efficient linearized analysis where the redshift errors are directly
related to shifts in the weak lensing convergence power spectra. We estimate
the number Nspec of unbiased spectroscopic redshifts needed to determine the
catastrophic error rate well enough that biases in cosmological parameters are
below statistical errors of weak lensing tomography. While the straightforward
estimate of Nspec is ~10^6 we find that using only the photometric redshifts
with z<=2.5 leads to a drastic reduction in Nspec to ~30,000 while negligibly
increasing statistical errors in dark energy parameters. Therefore, the size of
spectroscopic survey needed to control catastrophic errors is similar to that
previously deemed necessary to constrain the core of the z_s-z_p distribution.
We also study the efficacy of the recent proposal to measure redshift errors by
cross-correlation between the photo-z and spectroscopic samples. We find that
this method requires ~10% a priori knowledge of the bias and stochasticity of
the outlier population, and is also easily confounded by lensing magnification
bias. The cross-correlation method is therefore unlikely to supplant the need
for a complete spectroscopic redshift survey of the source population.Comment: 14 pages, 3 figure
The incidence and characteristics of venous thromboembolisms in paediatric-onset inflammatory bowel disease; a prospective international cohort study based on the PIBD-SETQuality Safety Registry.
BACKGROUND & AIMS: Guidelines regarding thromboprophylaxis for venous thromboembolisms (VTE) in children with inflammatory bowel disease (IBD) are based on limited paediatric evidence. We aimed to prospectively assess the incidence of VTE in paediatric-onset IBD (PIBD), characterize PIBD patients with VTE, and identify potential IBD-related risk factors. METHODS: From October 2016 till September 2020, paediatric gastroenterologists prospectively replied to the international Safety Registry, monthly indicating whether they had observed a VTE case in a patient <19 years with IBD. IBD details (type, Paris classification, clinical and biochemical disease activity, treatment) and VTE details (type, location, treatment, outcome) were collected. To estimate the VTE incidence, participants annually reported the number of PIBD patients, data source and catchment area of their center. A systematic literature review and meta-analysis was performed to calculate the VTE incidence in the general paediatric population. RESULTS: Participation of 129 PIBD centers resulted in coverage of 24,802 PIBD patients. Twenty cases of VTE were identified (30% Crohn's disease). The VTE incidence was 3.72 [95%CI 2.27 - 5.74] per 10,000 person-years, 14-fold higher than in the general paediatric population (0.27 [95%CI 0.18-0.38], p<0.001). Cerebral sinus venous thrombosis was most frequently reported (50%). All but one patient had active IBD, 45% were using steroids and 45% hospitalized. No patient received thromboprophylaxis, whereas according to current PIBD guidelines, this was recommended in 4/20 patients. CONCLUSION: There is an increased risk of VTE in the PIBD population compared to the general paediatric population. Awareness of VTE occurrence and prevention should be extended to all PIBD patients with active disease, especially those hospitalized
Large scale anisotropies on halo infall
We perform a statistical analysis of the peculiar velocity field around dark
matter haloes in numerical simulations. We examine different properties of the
infall of material onto haloes and its relation to central halo shapes and the
shape of the large scale surrounding regions (LSSR). We find that the amplitude
of the infall velocity field along the halo shape minor axis is larger than
that along the major axis. This is consistent for general triaxial haloes, and
for both prolate and oblate systems. We also report a strong anisotropy of the
velocity field along the principal axes of the LSSR. The infall velocity field
around dark matter haloes reaches a maximum value along the direction of the
minor axis of the LSSR, whereas along the direction of its major axis, it
exhibits the smallest velocities. We also analyse the dependence of the matter
velocity field on the local environment. The amplitude of the infall velocity
at high local density regions is larger than at low local density regions. The
velocity field tends to be more laminar along the direction towards the minor
axis of the LSSR, where the mean ratio between flow velocity and velocity
dispersion is of order unity and nearly constant up to scales of 15 Mpc/h. We
also detect anisotropies in the outflowing component of the velocity field,
showing a maximum amplitude along the surrounding LSSR major axis.Comment: 12 pages, 9 figures, accepted for publication in Monthly Notices of
the Royal Astronomical Societ
Accurate estimators of power spectra in N-body simulations
abridged] A method to rapidly estimate the Fourier power spectrum of a point
distribution is presented. This method relies on a Taylor expansion of the
trigonometric functions. It yields the Fourier modes from a number of FFTs,
which is controlled by the order N of the expansion and by the dimension D of
the system. In three dimensions, for the practical value N=3, the number of
FFTs required is 20. We apply the method to the measurement of the power
spectrum of a periodic point distribution that is a local Poisson realization
of an underlying stationary field. We derive explicit analytic expression for
the spectrum, which allows us to quantify--and correct for--the biases induced
by discreteness and by the truncation of the Taylor expansion, and to bound the
unknown effects of aliasing of the power spectrum. We show that these aliasing
effects decrease rapidly with the order N. The only remaining significant
source of errors is reduced to the unavoidable cosmic/sample variance due to
the finite size of the sample. The analytical calculations are successfully
checked against a cosmological N-body experiment. We also consider the initial
conditions of this simulation, which correspond to a perturbed grid. This
allows us to test a case where the local Poisson assumption is incorrect. Even
in that extreme situation, the third-order Fourier-Taylor estimator behaves
well. We also show how to reach arbitrarily large dynamic range in Fourier
space (i.e., high wavenumber), while keeping statistical errors in control, by
appropriately "folding" the particle distribution.Comment: 18 Pages, 9 Figures. Accepted for publication in MNRAS. The
Fourier-Taylor module as well as the associated power spectrum estimator tool
we propose is available as an F90 package, POWMES, at
http://www.projet-horizon.fr or on request from the author
Average Heating Rate of Hot Atmospheres in Distant Clusters by Radio AGN: Evidence for Continuous AGN Heating
We examine atmospheric heating by radio active galactic nuclei (AGN) in
distant X-ray clusters by cross correlating clusters selected from the 400
Square Degree (400SD) X-ray Cluster survey with radio sources in the NRAO VLA
Sky Survey. Roughly 30% of the clusters show radio emission above a flux
threshold of 3 mJy within a projected radius of 250 kpc. The radio emission is
presumably associated with the brightest cluster galaxy. The mechanical jet
power for each radio source was determined using scaling relations between
radio power and cavity (mechanical) power determined for nearby clusters,
groups, and galaxies with hot atmospheres containing X-ray cavities. The
average jet power of the central radio AGN is approximately \ergs. We find no significant correlation between radio power, hence
mechanical jet power, and the X-ray luminosities of clusters in the redshift
range 0.1 -- 0.6. This implies that the mechanical heating rate per particle is
higher in lower mass, lower X-ray luminosity clusters. The jet power averaged
over the sample corresponds to an atmospheric heating of approximately 0.2 keV
per particle within R. Assuming the current AGN heating rate does not
evolve but remains constant to redshifts of 2, the heating rate per particle
would rise by a factor of two. We find that the energy injected from radio AGN
contribute substantially to the excess entropy in hot atmospheres needed to
break self-similarity in cluster scaling relations. The detection frequency of
radio AGN is inconsistent with the presence of strong cooling flows in 400SD
clusters, but does not exclude weak cooling flows. It is unclear whether
central AGN in 400SD clusters are maintained by feedback at the base of a
cooling flow. Atmospheric heating by radio AGN may retard the development of
strong cooling flows at early epochs.Comment: ApJ in pres
Network-level consequences of outgroup threats in banded mongooses: grooming and aggression between the sexes
This is the final version. Available on open access from Wiley via the DOI in this record1) Animal groups are heterogeneous assemblages of individuals with differing fitness interests, which may lead to internal conflict over investment in group territorial defence. Differences between individuals may lead to different behavioural responses to intergroup conflict, particularly between the sexes. These potential impacts have been little studied.
2) We used social network analysis to investigate the impact of simulated intergroup conflicts on social relationships in groups of wild banded mongooses (Mungos mungo), in which intergroup fights are more costly for males than females. We predicted that social cohesion (specifically male-to-male and female-to-male grooming) would increase after conflict, and aggression would decrease, to minimise conflict between the sexes.
3) Simulated intergroup conflicts were performed by exposing banded mongoose groups to scents, “war cry” playbacks, and live intruders from a rival group. All grooming and aggression interactions between individuals were recorded, and grooming and aggression social networks were created for the two days preceding a simulated intergroup conflict (pre-conflict network) and the two days after (post-conflict network).
4) We found no evidence of an increase in social cohesion after simulated conflicts, measured as grooming eigenvector centrality. Male-to-male, male-to-female and female-to-male grooming strength decreased after simulated intrusions compared to female-to-female grooming strength. However, male-female aggression decreased in intrusion trials compared to other interaction types, consistent with the hypothesis that intergroup encounters reduce the level of intragroup conflict between males and females. Males were more affected socially by intergroup encounters than females, which may be because they are investing in defence rather than internal relationships.
5) Focusing on individual relationship changes, using social network analysis, can reveal changes in the directionality of behaviour in response to intergroup encounters, and highlight how individual responses to conflict may scale up to affect social networks and, potentially, group 69 performance. This study highlights the importance of studying both group level behaviours and individual relationships to more fully understand responses to intergroup encounters.Natural Environment Research Council (NERC
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