1,386 research outputs found
The Mean and Scatter of the Velocity Dispersion-Optical Richness Relation for maxBCG Galaxy Clusters
The distribution of galaxies in position and velocity around the centers of
galaxy clusters encodes important information about cluster mass and structure.
Using the maxBCG galaxy cluster catalog identified from imaging data obtained
in the Sloan Digital Sky Survey, we study the BCG-galaxy velocity correlation
function. By modeling its non-Gaussianity, we measure the mean and scatter in
velocity dispersion at fixed richness. The mean velocity dispersion increases
from 202+/-10 km/s for small groups to more than 854+/-102 km/s for large
clusters. We show the scatter to be at most 40.5+/-3.5%, declining to
14.9+/-9.4% in the richest bins. We test our methods in the C4 cluster catalog,
a spectroscopic cluster catalog produced from the Sloan Digital Sky Survey DR2
spectroscopic sample, and in mock galaxy catalogs constructed from N-body
simulations. Our methods are robust, measuring the scatter to well within
one-sigma of the true value, and the mean to within 10%, in the mock catalogs.
By convolving the scatter in velocity dispersion at fixed richness with the
observed richness space density function, we measure the velocity dispersion
function of the maxBCG galaxy clusters. Although velocity dispersion and
richness do not form a true mass-observable relation, the relationship between
velocity dispersion and mass is theoretically well characterized and has low
scatter. Thus our results provide a key link between theory and observations up
to the velocity bias between dark matter and galaxies.Comment: 25 pages, 15 figures, 2 tables, published in Ap
Estimates of in situ Larval Development Time for the Lobster, Homarus Americanus
Larval development time is a critical factor in assessing the potential for larval transport, mortality. and subsequently, the connectivity of marine populations through larval exchange. Most estimates of larval duration are based on laboratory studies and may not reflect development times in nature. For larvae of the American lobster (Homarus americanus), temperature-dependent development times have been established in previous laboratory studies. Here, we used the timing of seasonal abundance curves for newly hatched larvae (stage 1) and the final plankonic instar (postlarva), coupled with a model of temperature-dependent development to assess development time in the field. We were unable to reproduce the timing of the seasonal abundance curves using laboratory development rates in our model. Our results suggest that larval development in situ may be twice as fast as reported laboratory rates. This will result in reduced estimates of larval transport potential, and increased estimates of instantaneous mortality rate and production
Daya Terima Dan Kadar Betakaroten Donat Substitusi Labu Kuning
Vitamin A deïŹ ciency in Indonesia is still unresolved, especially in children. Pumpkin is a type of tubers and a local food product that contains high beta-carotene. It is also potential to be used as a substitution for snacks which favored by children such as donuts. The purpose of this study was to determine the acceptability and beta-carotene level of pumpkin donut substitution. This research was true experimental for product development and quasi experimental for acceptability with a completely randomized design, 6 repetitions on one control formula (F0) and 3 modiïŹ cation formula (F1, F2, F3) with additional of pumpkin. Panelist consists of 4 people as limited panelists and 30 people as non trained panelists. The difference of acceptability was analyze using Friedman test and continued with Wilcoxon Signed Rank Test if it shows a signiïŹ cant difference. The level of beta-carotene was analyze using spectrophotometer. The result of this study showed the best acceptability found in formula 3 (with 40% addition of pumpkin) with an average value of 2,28 and beta-carotene level of was 0,139 ppms. Formula 3 donut have a good acceptability and also contains higherbeta-carotene than commercial donuts, so it is potential as an alternative healthy snack for schoolchildren
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
Cross-correlation Weak Lensing of SDSS Galaxy Clusters III: Mass-to-light Ratios
We present measurements of the excess mass-to-light ratio measured
aroundMaxBCG galaxy clusters observed in the SDSS. This red sequence cluster
sample includes objects from small groups with masses ranging from ~5x10^{12}
to ~10^{15} M_{sun}/h. Using cross-correlation weak lensing, we measure the
excess mass density profile above the universal mean \Delta \rho(r) = \rho(r) -
\bar{\rho} for clusters in bins of richness and optical luminosity. We also
measure the excess luminosity density \Delta l(r) = l(r) - \bar{l} measured in
the z=0.25 i-band. For both mass and light, we de-project the profiles to
produce 3D mass and light profiles over scales from 25 kpc/ to 22 Mpc/h. From
these profiles we calculate the cumulative excess mass M(r) and excess light
L(r) as a function of separation from the BCG. On small scales, where \rho(r)
>> \bar{\rho}, the integrated mass-to-light profile may be interpreted as the
cluster mass-to-light ratio. We find the M/L_{200}, the mass-to-light ratio
within r_{200}, scales with cluster mass as a power law with index 0.33+/-0.02.
On large scales, where \rho(r) ~ \bar{\rho}, the M/L approaches an asymptotic
value independent of cluster richness. For small groups, the mean M/L_{200} is
much smaller than the asymptotic value, while for large clusters it is
consistent with the asymptotic value. This asymptotic value should be
proportional to the mean mass-to-light ratio of the universe . We find
/b^2_{ml} = 362+/-54 h (statistical). There is additional uncertainty in
the overall calibration at the ~10% level. The parameter b_{ml} is primarily a
function of the bias of the L <~ L_* galaxies used as light tracers, and should
be of order unity. Multiplying by the luminosity density in the same bandpass
we find \Omega_m/b^2_{ml} = 0.02+/-0.03, independent of the Hubble parameter.Comment: Third paper in a series; v2.0 incorporates ApJ referee's suggestion
Spectroscopy of Quasar Candidates from SDSS Commissioning Data
The Sloan Digital Sky Survey has obtained images in five broad-band colors
for several hundred square degrees. We present color-color diagrams for stellar
objects, and demonstrate that quasars are easily distinguished from stars by
their distinctive colors. Follow-up spectroscopy in less than ten nights of
telescope time has yielded 22 new quasars, 9 of them at , and one with
, the second highest-redshift quasar yet known. Roughly 80% of the
high-redshift quasar candidates selected by color indeed turn out to be
high-redshift quasars.Comment: 4 pages, 3 figures, to appear in the proceedings of "After the Dark
Ages: When Galaxies were Young (the Universe at 2<z<5)", 9th Annual October
Astrophysics Conference in Marylan
The changing face of floodplains in the Mississippi River Basin detected by a 60-year land use change dataset
Floodplains provide essential ecosystem functions, yet \u3e80% of European and North American floodplains are substantially modified. Despite floodplain changes over the past century, comprehensive, long-term land use change data within large river basin floodplains are limited. Long-term land use data can be used to quantify floodplain functions and provide spatially explicit information for management, restoration, and flood-risk mitigation. We present a comprehensive dataset quantifying floodplain land use change along the 3.3 million km2 Mississippi River Basin (MRB) covering 60 years (1941â2000) at 250-m resolution. We developed four unique products as part of this work, a(n): (i) Google Earth Engine interactive map visualization interface, (ii) Python code that runs in any internet browser, (iii) online tutorial with visualizations facilitating classroom code application, and (iv) instructional video demonstrating code application and database reproduction. Our data show that MRBâs natural floodplain ecosystems have been substantially altered to agricultural and developed land uses. These products will support MRB resilience and sustainability goals by advancing data-driven decision making on floodplain restoration, buyout, and conservation scenarios
SDSS-RASS: Next Generation of Cluster-Finding Algorithms
We outline here the next generation of cluster-finding algorithms. We show
how advances in Computer Science and Statistics have helped develop robust,
fast algorithms for finding clusters of galaxies in large multi-dimensional
astronomical databases like the Sloan Digital Sky Survey (SDSS). Specifically,
this paper presents four new advances: (1) A new semi-parametric algorithm -
nicknamed ``C4'' - for jointly finding clusters of galaxies in the SDSS and
ROSAT All-Sky Survey databases; (2) The introduction of the False Discovery
Rate into Astronomy; (3) The role of kernel shape in optimizing cluster
detection; (4) A new determination of the X-ray Cluster Luminosity Function
which has bearing on the existence of a ``deficit'' of high redshift, high
luminosity clusters. This research is part of our ``Computational
AstroStatistics'' collaboration (see Nichol et al. 2000) and the algorithms and
techniques discussed herein will form part of the ``Virtual Observatory''
analysis toolkit.Comment: To appear in Proceedings of MPA/MPE/ESO Conference "Mining the Sky",
July 31 - August 4, 2000, Garching, German
High-Redshift Quasars Found in Sloan Digital Sky Survey Commissioning Data III: A Color Selected Sample at i^*<20 in the Fall Equatorial Stripe
This is the third paper in a series aimed at finding high-redshift quasars
from five-color (u'g'r'i'z') imaging data taken along the Celestial Equator by
the SDSS during its commissioning phase. In this paper, we first present the
observations of 14 bright high-redshift quasars (3.66<z<4.77, i^*<20)
discovered in the SDSS Fall Equatorial Stripe, and the SDSS photometry of two
previously known high-redshift quasars in the same region of the sky. Combined
with the quasars presented in previous papers, we define a color-selected
flux-limited sample of 39 quasars at 3.6 < z < 5.0 and i^*<20, covering a total
effective area of 182 deg^2. From this sample, we estimate the average spectral
power law slope in the rest-frame ultraviolet for quasars at z~4 to be -0.79
with a standard deviation of 0.34, and the average rest-frame equivalent width
of the Ly alpha+N V emission line to be 69 A with a standard deviation of 18 A.
The selection completeness of this multicolor sample is determined from the
model colors of high-redshift quasars, taking into account the distributions of
emission line strengths, intrinsic continuum slope, the line and continuum
absorption from intervening material, and the effects of photometric errors.
The average completeness of this sample is about 75%. The selection function
calculated in this paper will be used to correct the incompleteness of this
color-selected sample and to derive the high-redshift quasar luminosity
function in a subsequent paper. In the Appendix, we present the observations of
an additional 18 faint quasars (3.57<z<4.80, 20.1<i^*<20.8) discovered in the
region on the sky that has been imaged twice. Several quasars presented in this
paper exhibit interesting properties, including a radio-loud quasar at z=4.77,
and a narrow-line quasar (FWHM = 1500 km s^-1) at z=3.57.Comment: AJ accepted (Jan 2001), with minor changes; high-resolution finding
charts available at http://www.sns.ias.edu/~fan/papers/q3.p
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