126 research outputs found
Hibernacula Site Selection of the Eastern Box Turtle, Terrapene c. carolina, in a West Virginia Population
Eastern Box Turtles (Terrapene c. carolina) are a terrestrially hibernating reptile found throughout the eastern United States. Despite their prevalence, little, outside of anecdotal observations, is known about their hibernacula selection. This study examines if they preferentially select hibernacula locations, and if so, what characteristics they select in a West Virginia population. Over the course of two years, radio-tagged turtles (n=12) were followed into hibernation in Wayne County, WV. Upon entering hibernation, ~36 data point were collected in a grid-like fashion around the hibernacula, with an additional point collected at the hibernacula. At each point, seven variables were recorded: soil temperature, soil compaction, soil moisture, soil pH, cover depth, cover moisture, and cover type. Results were analyzed using either categorical logistic regression for quantitative data or Ivlev’s (E) and Vanderploeg and Scavia’s (E*) electivity indices for categorical data. The conditional logistical regression showed a significant selection for both soil compaction (p=0.029) and cover depth (p=0.007). The two electivity indices showed a strong selection for mixed deciduous leaf litter as a cover type (E= 0.1264, E*= 0.4486). Thus, Eastern Box Turtles significantly select hibernacula sites with soft, friable soil, where they may dig easier, along with a thick cover of deciduous leaf litter, which provides increased insulation during the winter months. These results correspond with recorded anecdotal observations, thus suggesting this study may have validity throughout much of Terrapene c. carolina’s range, and provide an avenue for further study of their winter ecology, which is necessary for their continuing protection
Categorization, Intersectionality, and Learning Analytics
Extended abstract from the LAK 2018 Conference in Sydney AustraliaLearning analytics often relies on data produced by education systems which
include traditional categorical descriptors of identity. Uncritical use of these reductive
categories obscures the complexity of identity and masks the unique experience of each
student. If learning analytics is to accomplish its goal of understanding and improving
teaching and learning for all students, it must examine the methods it uses to account for
social identity more closely. In this work, we describe how feminist studies of
intersectionality have informed our own analysis of how social identity might influence
student performance in an array of large introductory courses.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/144579/1/LAK18 REA Categorization and Intersectionality in Learning Analytics v1.2.pdfDescription of LAK18 REA Categorization and Intersectionality in Learning Analytics v1.2.pdf : Main Articl
The Dust Content of Galaxy Clusters
We report on the detection of reddening toward z ~ 0.2 galaxy clusters. This
is measured by correlating the Sloan Digital Sky Survey cluster and quasar
catalogs and by comparing the photometric and spectroscopic properties of
quasars behind the clusters to those in the field. We find mean E(B-V) values
of a few times 10^-3 mag for sight lines passing ~Mpc from the clusters'
center. The reddening curve is typical of dust but cannot be used to
distinguish between different dust types. The radial dependence of the
extinction is shallow near the cluster center suggesting that most of the
detected dust lies at the outskirts of the clusters. Gravitational
magnification of background z ~ 1.7 sources seen on Mpc (projected) scales
around the clusters is found to be of order a few per cent, in qualitative
agreement with theoretical predictions. Contamination by different spectral
properties of the lensed quasar population is unlikely but cannot be excluded.Comment: 4 pages, 3 figure
Extrinsic Sources of Scatter in the Richness-Mass Relation of Galaxy Clusters
Maximizing the utility of upcoming photometric cluster surveys requires a
thorough understanding of the richness-mass relation of galaxy clusters. We use
Monte Carlo simulations to study the impact of various sources of observational
scatter on this relation. Cluster ellipticity, photometric errors, photometric
redshift errors, and cluster-to-cluster variations in the properties of
red-sequence galaxies contribute negligible noise. Miscentering, however, can
be important, and likely contributes to the scatter in the richness-mass
relation of galaxy maxBCG clusters at the low mass end, where centering is more
difficult. We also investigate the impact of projection effects under several
empirically motivated assumptions about cluster environments. Using SDSS data
and the maxBCG cluster catalog, we demonstrate that variations in cluster
environments can rarely (\approx 1% - 5% of the time) result in significant
richness boosts. Due to the steepness of the mass/richness function, the
corresponding fraction of optically selected clusters that suffer from these
projection effects is \approx 5% - 15%. We expect these numbers to be generic
in magnitude, but a precise determination requires detailed, survey-specific
modeling
Precision Measurements of the Cluster Red Sequence using an Error Corrected Gaussian Mixture Model
The red sequence is an important feature of galaxy clusters and plays a
crucial role in optical cluster detection. Measurement of the slope and scatter
of the red sequence are affected both by selection of red sequence galaxies and
measurement errors. In this paper, we describe a new error corrected Gaussian
Mixture Model for red sequence galaxy identification. Using this technique, we
can remove the effects of measurement error and extract unbiased information
about the intrinsic properties of the red sequence. We use this method to
select red sequence galaxies in each of the 13,823 clusters in the maxBCG
catalog, and measure the red sequence ridgeline location and scatter of each.
These measurements provide precise constraints on the variation of the average
red galaxy populations in the observed frame with redshift. We find that the
scatter of the red sequence ridgeline increases mildly with redshift, and that
the slope decreases with redshift. We also observe that the slope does not
strongly depend on cluster richness. Using similar methods, we show that this
behavior is mirrored in a spectroscopic sample of field galaxies, further
emphasizing that ridgeline properties are independent of environment.Comment: 33 pages, 14 Figures; A typo in Eq.A11 is fixed. The C++/Python codes
for ECGMM can be downloaded from:
https://sites.google.com/site/jiangangecgmm
Cross-correlation Weak Lensing of SDSS galaxy Clusters II: Cluster Density Profiles and the Mass--Richness Relation
We interpret and model the statistical weak lensing measurements around
130,000 groups and clusters of galaxies in the Sloan Digital Sky Survey
presented by Sheldon et al. 2007 (Paper I). We present non-parametric
inversions of the 2D shear profiles to the mean 3D cluster density and mass
profiles in bins of both optical richness and cluster i-band luminosity. We
correct the inferred 3D profiles for systematic effects, including non-linear
shear and the fact that cluster halos are not all precisely centered on their
brightest galaxies. We also model the measured cluster shear profile as a sum
of contributions from the brightest central galaxy, the cluster dark matter
halo, and neighboring halos. We infer the relations between mean cluster virial
mass and optical richness and luminosity over two orders of magnitude in
cluster mass; the virial mass at fixed richness or luminosity is determined
with a precision of 13% including both statistical and systematic errors. We
also constrain the halo concentration parameter and halo bias as a function of
cluster mass; both are in good agreement with predictions of LCDM models. The
methods employed here will be applicable to deeper, wide-area optical surveys
that aim to constrain the nature of the dark energy, such as the Dark Energy
Survey, the Large Synoptic Survey Telescope and space-based surveys
Constraining the Scatter in the Mass-Richness Relation of maxBCG Clusters With Weak Lensing and X-ray Data
We measure the logarithmic scatter in mass at fixed richness for clusters in
the maxBCG cluster catalog, an optically selected cluster sample drawn from
SDSS imaging data. Our measurement is achieved by demanding consistency between
available weak lensing and X-ray measurements of the maxBCG clusters, and the
X-ray luminosity--mass relation inferred from the 400d X-ray cluster survey, a
flux limited X-ray cluster survey. We find \sigma_{\ln
M|N_{200}}=0.45^{+0.20}_{-0.18} (95% CL) at N_{200} ~ 40, where N_{200} is the
number of red sequence galaxies in a cluster. As a byproduct of our analysis,
we also obtain a constraint on the correlation coefficient between \ln Lx and
\ln M at fixed richness, which is best expressed as a lower limit, r_{L,M|N} >=
0.85 (95% CL). This is the first observational constraint placed on a
correlation coefficient involving two different cluster mass tracers. We use
our results to produce a state of the art estimate of the halo mass function at
z=0.23 -- the median redshift of the maxBCG cluster sample -- and find that it
is consistent with the WMAP5 cosmology. Both the mass function data and its
covariance matrix are presented.Comment: 14 pages, 6 figures, submitted to Ap
Cosmological Constraints from the SDSS maxBCG Cluster Catalog
We use the abundance and weak lensing mass measurements of the SDSS maxBCG
cluster catalog to simultaneously constrain cosmology and the richness--mass
relation of the clusters. Assuming a flat \LambdaCDM cosmology, we find
\sigma_8(\Omega_m/0.25)^{0.41} = 0.832\pm 0.033 after marginalization over all
systematics. In common with previous studies, our error budget is dominated by
systematic uncertainties, the primary two being the absolute mass scale of the
weak lensing masses of the maxBCG clusters, and uncertainty in the scatter of
the richness--mass relation. Our constraints are fully consistent with the WMAP
five-year data, and in a joint analysis we find \sigma_8=0.807\pm 0.020 and
\Omega_m=0.265\pm 0.016, an improvement of nearly a factor of two relative to
WMAP5 alone. Our results are also in excellent agreement with and comparable in
precision to the latest cosmological constraints from X-ray cluster abundances.
The remarkable consistency among these results demonstrates that cluster
abundance constraints are not only tight but also robust, and highlight the
power of optically-selected cluster samples to produce precision constraints on
cosmological parameters.Comment: comments welcom
Alignment of Brightest Cluster Galaxies with their Host Clusters
We examine the alignment between Brightest Cluster Galaxies (BCGs) and their
host clusters in a sample of 7031 clusters with 0.08<z<0.44 found using a
matched-filter algorithm and an independent sample of 5744 clusters with
0.1<z<0.3 selected with the maxBCG algorithm, both extracted from the Sloan
Digital Sky Survey Data Release 6 imaging data. We confirm that BCGs are
preferentially aligned with the cluster's major axis; clusters with dominant
BCGs (>0.65 mag brighter than the mean of the second and third ranked galaxies)
show stronger alignment than do clusters with less dominant BCGs at the 4.4
sigma level. Rich clusters show a stronger alignment than do poor clusters at
the 2.3 sigma level. Low redshift clusters (z<0.26) show more alignment than do
high redshift (z>0.26) clusters, with a difference significant at the 3.0 sigma
level. Our results do not depend on the algorithm used to select the cluster
sample, suggesting that they are not biased by systematics of either algorithm.
The correlation between BCG dominance and cluster alignment may be a
consequence of the hierarchical merging process which forms the cluster. The
observed redshift evolution may follow from secondary infall at late redshifts.Comment: 15 pages, 12 Figures, 10 Tables, Accepted for publication in MNRA
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