161,151 research outputs found
The Variance of QSO Counts in Cells
{}From three quasar samples with a total of 1038 objects in the redshift
range we measure the variance of counts in cells of
volume . By a maximum likelihood analysis applied separately on these
samples we obtain estimates of , with .
The analysis from a single catalog for Mpc and from a
suitable average over the three catalogs for and
Mpc, gives , ,
and , respectively, where the
confidence ranges account for both sampling errors and statistical
fluctuations in the counts. This allows a comparison of QSO clustering on large
scales with analogous data recently obtained both for optical and IRAS
galaxies: QSOs seem to be more clustered than these galaxies by a biasing
factor .Comment: 13 pages in plain Tex, 5 figures available in postscript in a
separate file, submitted to ApJ, DAPD-33
Halo-model Analysis of the Clustering of Photometrically Selected Galaxies from SDSS
We measure the angular 2-point correlation functions of galaxies in a volume
limited, photometrically selected galaxy sample from the fifth data release of
the Sloan Digital Sky Survey. We split the sample both by luminosity and galaxy
type and use a halo-model analysis to find halo-occupation distributions that
can simultaneously model the clustering of all, early-, and late-type galaxies
in a given sample. Our results for the full galaxy sample are generally
consistent with previous results using the SDSS spectroscopic sample, taking
the differences between the median redshifts of the photometric and
spectroscopic samples into account. We find that our early- and late- type
measurements cannot be fit by a model that allows early- and late-type galaxies
to be well-mixed within halos. Instead, we introduce a new model that
segregates early- and late-type galaxies into separate halos to the maximum
allowed extent. We determine that, in all cases, it provides a good fit to our
data and thus provides a new statistical description of the manner in which
early- and late-type galaxies occupy halos.Comment: Accepted to MNRAS 11 pages, 6 figure
Paradigm of tunable clustering using binarization of consensus partition matrices (Bi-CoPaM) for gene discovery
Copyright @ 2013 Abu-Jamous et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Clustering analysis has a growing role in the study of co-expressed genes for gene discovery. Conventional binary and fuzzy clustering do not embrace the biological reality that some genes may be irrelevant for a problem and not be assigned to a cluster, while other genes may participate in several biological functions and should simultaneously belong to multiple clusters. Also, these algorithms cannot generate tight clusters that focus on their cores or wide clusters that overlap and contain all possibly relevant genes. In this paper, a new clustering paradigm is proposed. In this paradigm, all three eventualities of a gene being exclusively assigned to a single cluster, being assigned to multiple clusters, and being not assigned to any cluster are possible. These possibilities are realised through the primary novelty of the introduction of tunable binarization techniques. Results from multiple clustering experiments are aggregated to generate one fuzzy consensus partition matrix (CoPaM), which is then binarized to obtain the final binary partitions. This is referred to as Binarization of Consensus Partition Matrices (Bi-CoPaM). The method has been tested with a set of synthetic datasets and a set of five real yeast cell-cycle datasets. The results demonstrate its validity in generating relevant tight, wide, and complementary clusters that can meet requirements of different gene discovery studies.National Institute for Health Researc
The Imperial IRAS-FSC Redshift Catalogue: luminosity functions, evolution and galaxy bias
We present the luminosity function and selection function of 60 micron
galaxies selected from the Imperial IRAS-FSC Redshift Catalogue (IIFSCz). Three
methods, including the 1/Vmax} and the parametric and non-parametric maximum
likelihood estimator, are used and results agree well with each other. A
density evolution proportional to (1+z)^3.4 or a luminosity evolution exp(1.7
t_L / \tau)$ where t_L is the look-back time is detected in the full sample in
the redshift range [0.02, 0.1], consistent with previous analyses. Of the four
infrared subpopulations, cirrus-type galaxies and M82-type starbursts show
similar evolutionary trends, galaxies with significant AGN contributions show
stronger positive evolution and Arp 220-type starbursts exhibit strong negative
evolution. The dominant subpopulation changes from cirrus-type galaxies to
M82-type starbursts at log (L_60 / L_Sun) ~ 10.3.
In the second half of the paper, we derive the projected two-point spatial
correlation function for galaxies of different infrared template type. The mean
relative bias between cirrus-type galaxies and M82-type starbursts, which
correspond to quiescent galaxies with optically thin interstellar dust and
actively star-forming galaxies respectively, is calculated to be around 1.25.
The relation between current star formation rate (SFR) in star-forming galaxies
and environment is investigated by looking at the the dependence of clustering
on infrared luminosity. We found that M82-type actively star-forming galaxies
show stronger clustering as infrared luminosity / SFR increases. The
correlation between clustering strength and SFR in the local Universe seems to
echo the basic trend seen in star-forming galaxies in the Great Observatories
Origins Deep Survey (GOODS) fields at z ~ 1.Comment: 15 pages, 11 figures, accepted for publication in MNRA
Continuous Fields and Discrete Samples: Reconstruction through Delaunay Tessellations
Here we introduce the Delaunay Density Estimator Method. Its purpose is
rendering a fully volume-covering reconstruction of a density field from a set
of discrete data points sampling this field. Reconstructing density or
intensity fields from a set of irregularly sampled data is a recurring key
issue in operations on astronomical data sets, both in an observational context
as well as in the context of numerical simulations. Our technique is based upon
the stochastic geometric concept of the Delaunay tessellation generated by the
point set. We shortly describe the method, and illustrate its virtues by means
of an application to an N-body simulation of cosmic structure formation. The
presented technique is a fully adaptive method: automatically it probes high
density regions at maximum possible resolution, while low density regions are
recovered as moderately varying regions devoid of the often irritating
shot-noise effects. Of equal importance is its capability to sharply and
undilutedly recover anisotropic density features like filaments and walls. The
prominence of such features at a range of resolution levels within a
hierarchical clustering scenario as the example of the standard CDM scenario is
shown to be impressively recovered by our scheme.Comment: 4 pages, 2 figures, accepted for publication in Astronomy &
Astrophysics Letter
Preferential concentration of inertial sub-kolmogorov particles. The roles of mass loading of particles, Stokes and Reynolds numbers
Turbulent flows laden with inertial particles present multiple open questions
and are a subject of great interest in current research. Due to their higher
density compared to the carrier fluid, inertial particles tend to form high
concentration regions, i.e. clusters, and low concentration regions, i.e.
voids, due to the interaction with the turbulence. In this work, we present an
experimental investigation of the clustering phenomenon of heavy sub-Kolmogorov
particles in homogeneous isotropic turbulent flows. Three control parameters
have been varied over significant ranges: ,
and volume fraction . The scaling of clustering characteristics, such as the distribution
of Vorono\"i areas and the dimensions of cluster and void regions, with the
three parameters are discussed. In particular, for the polydispersed size
distributions considered here, clustering is found to be enhanced strongly
(quasi-linearly) by and noticeably (with a square-root
dependency) with , while the cluster and void sizes, scaled with the
Kolmogorov lengthscale , are driven primarily by . Cluster
length scales up to , measured
at the highest , while void length
scaled also with is typically two times larger ().
The lack of sensitivity of the above characteristics to the Stokes number lends
support to the "sweep-stick" particle accumulation scenario. The non-negligible
influence of the volume fraction, however, is not considered by that model and
can be connected with collective effects
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