79 research outputs found
Nuisance
This essay sets out the law and the economic theory of nuisance. Nuisance law serves a regulatory function: it induces actors to choose the socially preferred level of an activity by imposing liability when the externalized costs of the activity are substantially greater than the externalized benefits or not reciprocal to other background external costs. Proximate cause doctrine plays a role in supplementing nuisance law
Weak lensing survey of galaxy clusters in the CFHTLS Deep
AIMS: We present a weak lensing search of galaxy clusters in the 4 deg2 of
the CFHT Legacy Survey Deep. This work aims at building a mass-selected sample
of clusters. METHODS: We use the deep i' band images to perform weak lensing
mass reconstructions and to identify high convergence peaks. Thanks to the
availability of deep ugriz exposures, sources are selected from their
photometric redshifts. We also use lensing tomography to derive an estimate of
the lens redshift. After considering the raw statistics of peaks we check
whether they can be associated to a clear optical counterpart or to published
X-ray selected clusters. RESULTS: Among the 14 peaks found above a
signal-to-noise detection threshold nu=3.5, eight are secure detections with
estimated redshift 0.15<zl<0.6 and a velocity dispersion 450<sigma\_v<600 km/s.
This low mass range is accessible thanks to the high density of background
sources. We also use photometric redshifts of sources to test the effect of
contamination by source-lens clustering for clusters detection. This latter
turns out to play a minor role in our cluster sample. We study the intersection
between the shear-selected clusters and XMM/LSS X-ray clusters in the D1 field.
[ABRIDGED]Comment: A&A accepted. Several major changes. Full version available at
http://www.ast.obs-mip.fr/users/soucail/clusters_cfhtls.pd
The Structure of 2MASS Galaxy Clusters
We use a sample of galaxies from the Two Micron All Sky Survey (2MASS)
Extended Source Catalog to refine a matched filter method of finding galaxy
clusters that takes into account each galaxy's position, magnitude, and
redshift if available. The matched filter postulates a radial density profile,
luminosity function, and line-of-sight velocity distribution for cluster
galaxies. We use this method to search for clusters in the galaxy catalog,
which is complete to an extinction-corrected K-band magnitude of 13.25 and has
spectroscopic redshifts for roughly 40% of the galaxies, including nearly all
brighter than K = 11.25. We then use a stacking analysis to determine the
average luminosity function, radial distribution, and velocity distribution of
cluster galaxies in several richness classes, and use the results to update the
parameters of the matched filter before repeating the cluster search. We also
investigate the correlations between a cluster's richness and its velocity
dispersion and core radius, using these relations to refine priors that are
applied during the cluster search process. After the second cluster search
iteration, we repeat the stacking analysis. We find a cluster galaxy luminosity
function that fits a Schechter form, with parameters M_K* - 5 log h =
-23.64\pm0.04 and \alpha = -1.07\pm0.03. We can achieve a slightly better fit
to our luminosity function by adding a Gaussian component on the bright end to
represent the brightest cluster galaxy (BCG) population. The radial number
density profile of galaxies closely matches a projected Navarro-Frenk-White
(NFW) profile at intermediate radii, with deviations at small radii due to
well-known cluster centering issues and outside the virial radius due to
correlated structure. The velocity distributions are Gaussian in shape, with
velocity dispersions that correlate strongly with richness.Comment: 13 pages, 10 figures, 3 tables. Updated to match version published in
Ap
Divergent platforms
Models of electoral competition between two opportunistic, office-motivated parties typically predict that both parties become indistinguishable in equilibrium. I show that this strong connection between the office motivation of parties and their equilibrium choice of identical platforms depends on two—possibly false—assumptions: (1) Issue spaces are uni-dimensional and (2) Parties are unitary actors whose preferences can be represented by expected utilities. I provide an example of a two-party model in which parties offer substantially different equilibrium platforms even though no exogenous differences between parties are assumed. In this example, some voters’ preferences over the 2-dimensional issue space exhibit non-convexities and parties evaluate their actions with respect to a set of beliefs on the electorate
Fitting the integrated Spectral Energy Distributions of Galaxies
Fitting the spectral energy distributions (SEDs) of galaxies is an almost
universally used technique that has matured significantly in the last decade.
Model predictions and fitting procedures have improved significantly over this
time, attempting to keep up with the vastly increased volume and quality of
available data. We review here the field of SED fitting, describing the
modelling of ultraviolet to infrared galaxy SEDs, the creation of
multiwavelength data sets, and the methods used to fit model SEDs to observed
galaxy data sets. We touch upon the achievements and challenges in the major
ingredients of SED fitting, with a special emphasis on describing the interplay
between the quality of the available data, the quality of the available models,
and the best fitting technique to use in order to obtain a realistic
measurement as well as realistic uncertainties. We conclude that SED fitting
can be used effectively to derive a range of physical properties of galaxies,
such as redshift, stellar masses, star formation rates, dust masses, and
metallicities, with care taken not to over-interpret the available data. Yet
there still exist many issues such as estimating the age of the oldest stars in
a galaxy, finer details ofdust properties and dust-star geometry, and the
influences of poorly understood, luminous stellar types and phases. The
challenge for the coming years will be to improve both the models and the
observational data sets to resolve these uncertainties. The present review will
be made available on an interactive, moderated web page (sedfitting.org), where
the community can access and change the text. The intention is to expand the
text and keep it up to date over the coming years.Comment: 54 pages, 26 figures, Accepted for publication in Astrophysics &
Space Scienc
Nutritional Asymmetries Are Related to Division of Labor in a Queenless Ant
Eusocial species exhibit pronounced division of labor, most notably between reproductive and non-reproductive castes, but also within non-reproductive castes via morphological specialization and temporal polyethism. For species with distinct worker and queen castes, age-related differences in behavior among workers (e.g. within-nest tasks versus foraging) appear to result from physiological changes such as decreased lipid content. However, we know little about how labor is divided among individuals in species that lack a distinct queen caste. In this study, we investigated how fat storage varied among individuals in a species of ant (Dinoponera australis) that lacks a distinct queen caste and in which all individuals are morphologically similar and capable of reproduction (totipotent at birth). We distinguish between two hypotheses, 1) all individuals are physiologically similar, consistent with the possibility that any non-reproductive may eventually become reproductive, and 2) non-reproductive individuals vary in stored fat, similar to highly eusocial species, where depletion is associated with foraging and non-reproductives have lower lipid stores than reproducing individuals. Our data support the latter hypothesis. Location in the nest, the probability of foraging, and foraging effort, were all associated with decreased fat storage
Photometric redshifts for the next generation of deep radio continuum surveys - I: template fitting
We present a study of photometric redshift performance for galaxies and active galactic nuclei detected in deep radio continuum surveys. Using two multi-wavelength datasets, over the NOAO Deep Wide Field Survey Boötes and COSMOS fields, we assess photometric redshift (photo-z) performance for a sample of 4; 500 radio continuum sources with spectroscopic redshifts relative to those of 63; 000 non radio-detected sources in the same fields. We investigate the performance of three photometric redshift template sets as a function of redshift, radio luminosity and infrared/X-ray properties. We find that no single template library is able to provide the best performance across all subsets of the radio detected population, with variation in the optimum template set both between subsets and between fields. Through a hierarchical Bayesian combination of the photo-z estimates from all three template sets, we are able to produce a consensus photo-z estimate which equals or improves upon the performance of any individual template set
The DES bright arcs survey: hundreds of candidate strongly lensed galaxy systems from the Dark Energy Survey Science Verification and year 1 observations
We report the results of searches for strong gravitational lens systems in the Dark Energy Survey (DES) Science Verification and Year 1 observations. The Science Verification data span approximately 250 sq. deg. with a median i-band limiting magnitude for extended objects (10σ) of 23.0. The Year 1 data span approximately 2000 sq. deg. and have an i-band limiting magnitude for extended objects (10σ) of 22.9. As these data sets are both wide and deep, they are particularly useful for identifying strong gravitational lens candidates. Potential strong gravitational lens candidate systems were initially identified based on a color and magnitude selection in the DES object catalogs or because the system is at the location of a previously identified galaxy cluster. Cutout images of potential candidates were then visually scanned using an object viewer and numerically ranked according to whether or not we judged them to be likely strong gravitational lens systems. Having scanned nearly 400,000 cutouts, we present 374 candidate strong lens systems, of which 348 are identified for the first time. We provide the R.A. and decl., the magnitudes and photometric properties of the lens and source objects, and the distance (radius) of the source(s) from the lens center for each system
Shedding Light on the Galaxy Luminosity Function
From as early as the 1930s, astronomers have tried to quantify the
statistical nature of the evolution and large-scale structure of galaxies by
studying their luminosity distribution as a function of redshift - known as the
galaxy luminosity function (LF). Accurately constructing the LF remains a
popular and yet tricky pursuit in modern observational cosmology where the
presence of observational selection effects due to e.g. detection thresholds in
apparent magnitude, colour, surface brightness or some combination thereof can
render any given galaxy survey incomplete and thus introduce bias into the LF.
Over the last seventy years there have been numerous sophisticated
statistical approaches devised to tackle these issues; all have advantages --
but not one is perfect. This review takes a broad historical look at the key
statistical tools that have been developed over this period, discussing their
relative merits and highlighting any significant extensions and modifications.
In addition, the more generalised methods that have emerged within the last few
years are examined. These methods propose a more rigorous statistical framework
within which to determine the LF compared to some of the more traditional
methods. I also look at how photometric redshift estimations are being
incorporated into the LF methodology as well as considering the construction of
bivariate LFs. Finally, I review the ongoing development of completeness
estimators which test some of the fundamental assumptions going into LF
estimators and can be powerful probes of any residual systematic effects
inherent magnitude-redshift data.Comment: 95 pages, 23 figures, 3 tables. Now published in The Astronomy &
Astrophysics Review. This version: bring in line with A&AR format
requirements, also minor typo corrections made, additional citations and
higher rez images adde
Historical Human Footprint on Modern Tree Species Composition in the Purus-Madeira Interfluve, Central Amazonia
Background: Native Amazonian populations managed forest resources in numerous ways, often creating oligarchic forests dominated by useful trees. The scale and spatial distribution of forest modification beyond pre-Columbian settlements is still unknown, although recent studies propose that human impact away from rivers was minimal. We tested the hypothesis that past human management of the useful tree community decreases with distance from rivers. Methodology/Principal Findings: In six sites, we inventoried trees and palms with DBH≥10 cm and collected soil for charcoal analysis; we also mapped archaeological evidence around the sites. To quantify forest manipulation, we measured the relative abundance, richness and basal area of useful trees and palms. We found a strong negative exponential relationship between forest manipulation and distance to large rivers. Plots located from 10 to 20 km from a main river had 20-40% useful arboreal species, plots between 20 and 40 km had 12-23%, plots more than 40 km had less than 15%. Soil charcoal abundance was high in the two sites closest to secondary rivers, suggesting past agricultural practices. The shortest distance between archaeological evidence and plots was found in sites near rivers. Conclusions/Significance: These results strongly suggest that past forest manipulation was not limited to the pre-Columbian settlements along major rivers, but extended over interfluvial areas considered to be primary forest today. The sustainable use of Amazonian forests will be most effective if it considers the degree of past landscape domestication, as human-modified landscapes concentrate useful plants for human sustainable use and management today. © 2012 Levis et al
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