53,549 research outputs found
The Ellipticity and Orientation of Clusters of Galaxies from N-Body Experiments
In this study we use simulations of 128 particles to study the
ellipticity and orientation of clusters of galaxies in N-body simulations of
differing power-law initial spectra (P(k) \propto k^n ,n = +1, 0, -1, -2\Omega_0 = 0.2nD < 15 h^{-1}n-$dependent way.Comment: 22 pages, requires aaspp4.sty, flushrt.sty, and epsf.sty Revised
manuscript, accepted for publication in Ap
Correspondence matching with modal clusters
The modal correspondence method of Shapiro and Brady aims to match point-sets by comparing the eigenvectors of a pairwise point proximity matrix. Although elegant by means of its matrix representation, the method is notoriously susceptible to differences in the relational structure of the point-sets under consideration. In this paper, we demonstrate how the method can be rendered robust to structural differences by adopting a hierarchical approach. To do this, we place the modal matching problem in a probabilistic setting in which the correspondences between pairwise clusters can be used to constrain the individual point correspondences. We demonstrate the utility of the method on a number of synthetic and real-world point-pattern matching problems
Feature Trajectory Dynamic Time Warping for Clustering of Speech Segments
Dynamic time warping (DTW) can be used to compute the similarity between two
sequences of generally differing length. We propose a modification to DTW that
performs individual and independent pairwise alignment of feature trajectories.
The modified technique, termed feature trajectory dynamic time warping (FTDTW),
is applied as a similarity measure in the agglomerative hierarchical clustering
of speech segments. Experiments using MFCC and PLP parametrisations extracted
from TIMIT and from the Spoken Arabic Digit Dataset (SADD) show consistent and
statistically significant improvements in the quality of the resulting clusters
in terms of F-measure and normalised mutual information (NMI).Comment: 10 page
HST, radio and infrared observations of 28 3CR radio galaxies at redshift z ~ 1: I. Old stellar populations in central cluster galaxies
Hubble Space Telescope images of 3CR radio galaxies at redshifts 0.6 < z <
1.8 have shown a remarkable variety of structures, generally aligned along the
radio axis, indicating that the radio source strongly influences the optical
appearance of these galaxies. In this paper we investigate the host galaxies
underlying this aligned emission, combining the HST data with ground-based
infrared images. An investigation of the spectral energy distributions of the
galaxies shows that the contribution of the aligned blue component to the
K--band light is generally small (about 10%). The radial intensity profiles of
the galaxies are well matched at radii <~ 35 kpc by de Vaucouleurs' law,
demonstrating that the K--band light is dominated by that of an elliptical
galaxy. There is no evidence for a nuclear point source, in addition to the de
Vaucouleurs profile, with a contribution >~15% of the total K--band flux
density, except in two cases, 3C22 and 3C41. Large characteristic radii are
derived, indicating that the 3CR galaxies must be highly evolved dynamically,
even at a redshift of one. At radii > 35 kpc, a combined galaxy profile clearly
shows an excess of emission reminiscent of cD--type halos. This supports other
independent evidence for the hypothesis that the distant 3CR galaxies lie in
moderately rich (proto--)clusters. Since the nearby FR II galaxies in the 3CR
catalogue lie in more diffuse environments and do not possess cD halos, the
galactic environments of the 3CR galaxies must change with redshift. The K-z
relation of the 3CR galaxies cannot, therefore, be interpreted using a standard
`closed-box, passive stellar evolution' model. We offer a new interpretation,
and compare the model with the K-z relations of lower power radio galaxies and
brightest cluster galaxies. (abridged)Comment: 21 pages including 13 figures, LaTeX. To appear in MNRA
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