11 research outputs found
Discovery of Extreme Examples of Superclustering in Aquarius
We report the discovery of two highly extended filaments and one extremely
high density knot within the region of Aquarius. The supercluster candidates
were chosen via percolation analysis of the Abell and ACO catalogs and include
only the richest clusters (R >= 1). The region examined is a 10x45 degree strip
and is now 87% complete in cluster redshift measurements to mag_10 = 18.3. In
all, we report 737 galaxy redshifts in 46 cluster fields. One of the
superclusters, dubbed Aquarius, is comprised of 14 Abell/ACO clusters and
extends 110h^-1Mpc in length only 7 degrees off the line-of-sight. On the
near-end of the Aquarius filament, another supercluster, dubbed Aquarius-Cetus,
extends for 75h^-1Mpc perpendicular to the line-of-sight. After fitting
ellipsoids to both Aquarius and Aquarius-Cetus, we find axis ratios (long-to-
midlength axis) of 4.3 for Aquarius and 3.0 for Aquarius-Cetus. We fit
ellipsoids to all N>=5 clumps of clusters in the Abell/ACO measured-z cluster
sample. The frequency of filaments with axis ratios >=3.0 (~20%) is nearly
identical with that found among `superclusters' in Monte Carlo simulations of
random and random- clumped clusters, however, so the rich Abell/ACO clusters
have no particular tendency toward filamentation. The Aquarius filament also
contains a `knot' of 6 clusters at Z ~0.11, with five of the clusters near
enough togeteher to represent an apparent overdensity of 150. There are
three other R >= 1 cluster density enhancements similar to this knot at lower
redshifts: Corona Borealis, the Shapely Concentration, and another grouping of
seven clusters in Microscopium. All four of these dense superclusters appear
near the point of breaking away from the Hubble Flow, and some may now be in
collapse, but there is little evidence of any being virialized.Comment: 45 pages (+ e-tables), 7 figures, AASTeX Accepted for Publication in
Ap
Noncommutative ball maps
In this paper, we analyze problems involving matrix variables for which we
use a noncommutative algebra setting. To be more specific, we use a class of
functions (called NC analytic functions) defined by power series in
noncommuting variables and evaluate these functions on sets of matrices of all
dimensions; we call such situations dimension-free. These types of functions
have recently been used in the study of dimension-free linear system
engineering problems.
In this paper we characterize NC analytic maps that send dimension-free
matrix balls to dimension-free matrix balls and carry the boundary to the
boundary; such maps we call "NC ball maps". We find that up to normalization,
an NC ball map is the direct sum of the identity map with an NC analytic map of
the ball into the ball. That is, "NC ball maps" are very simple, in contrast to
the classical result of D'Angelo on such analytic maps over C. Another
mathematically natural class of maps carries a variant of the noncommutative
distinguished boundary to the boundary, but on these our results are limited.
We shall be interested in several types of noncommutative balls, conventional
ones, but also balls defined by constraints called Linear Matrix Inequalities
(LMI). What we do here is a small piece of the bigger puzzle of understanding
how LMIs behave with respect to noncommutative change of variables.Comment: 46 page
Projection, Spatial Correlations, and Anisotropies in a Large and Complete Sample of Abell Clusters
An analysis of R >= 1 Abell clusters is presented for samples containing
recent redshifts from the MX Northern Abell Cluster Survey. The newly obtained
redshifts from the MX Survey as well as those from the ESO Nearby Abell Cluster
Survey (ENACS) provide the necessary data for the largest magnitude-limited
correlation analysis of rich clusters in the entire sky (excluding the galactic
plane) to date. We find 19.4 <= r_0 <= 23.3 h^-1Mpc, -1.92 <= gamma <= -1.83
for four different subsets of Abell/ACO clusters, including a large sample
(N=104) of cD clusters. We have used this dataset to look for line-of-sight
anisotropies within the Abell/ACO catalogs. We show that the strong
anisotropies present in previously studied Abell cluster datasets are not
present in our R >= 1 samples. There are, however, indications of residual
anisotropies which we show are the result of two elongated superclusters, Ursa
Majoris and Corona Borealis, whose axes lie near the line-of-sight. After
rotating these superclusters so that their semi-major axes are prependicular to
the line-of-sight, we find no anisotropies as indicated by the correlation
function. The amplitude and slope of the two-point correlation function remain
the same before and after these rotations. We also remove a subset of R = 1
Abell/ACO clusters that show sizable foreground/background galaxy contamination
and again find no change in the amplitude or slope of the correlation function.
We conclude that the correlation length of R >= 1 Abell clusters is not
artificially enhanced by line-of-sight anisotropies.Comment: 37 pages, 8 figures, AASTeX Accepted for publication in Ap
Infall Regions and Scaling Relations of X-ray Selected Groups
We use the Fifth Data Release of the Sloan Digital Sky Survey to study
X-ray-selected galaxy groups and compare their properties to clusters. We
search for infall patterns around the groups and use these to measure group
mass profiles to large radii. In previous work, we analyzed infall patterns for
an X-ray-selected sample of 72 clusters from the ROSAT All-Sky Survey. Here, we
extend this approach to a sample of systems with smaller X-ray fluxes selected
from the 400 Square Degree serendipitous survey of clusters and groups in ROSAT
pointed observations. We identify 16 groups with SDSS DR5 spectroscopy, search
for infall patterns, and compute mass profiles out to 2-6 Mpc from the group
centers with the caustic technique. No other mass estimation methods are
currently available at such large radii for these low-mass groups, because the
virial estimate requires dynamical equilibrium and the gravitational lensing
signal is too weak. Despite the small masses of these groups, most display
recognizable infall patterns. We use caustic and virial mass estimates to
measure the scaling relations between different observables, extending these
relations to smaller fluxes and luminosities than many previous surveys. Close
inspection reveals that three of the groups are subclusters in the outskirts of
larger clusters. A fourth group is apparently undergoing a group-group merger.
These four merging groups represent the most extreme outliers in the scaling
relations. Excluding these groups, we find ,
consistent with previous determinations for both clusters and groups.
Understanding cluster and group scaling relations is crucial for measuring
cosmological parameters from clusters.Comment: published in AJ Feb 2010, significantly revised in response to
referee report, title edite
The architecture of Abell 1386 and its relationship to the Sloan Great Wall
We present new radial velocities from AAOmega on the Anglo-Australian
Telescope for 307 galaxies (b_J < 19.5) in the region of the rich cluster Abell
1386. Consistent with other studies of galaxy clusters that constitute
sub-units of superstructures, we find that the velocity distribution of A1386
is very broad (21,000--42,000 kms^-1, or z=0.08--0.14) and complex. The mean
redshift of the cluster that Abell designated as number 1386 is found to be
~0.104. However, we find that it consists of various superpositions of
line-of-sight components. We investigate the reality of each component by
testing for substructure and searching for giant elliptical galaxies in each
and show that A1386 is made up of at least four significant clusters or groups
along the line of sight whose global parameters we detail. Peculiar velocities
of brightest galaxies for each of the groups are computed and found to be
different from previous works, largely due to the complexity of the sky area
and the depth of analysis performed in the present work. We also analyse A1386
in the context of its parent superclusters: Leo A, and especially the Sloan
Great Wall. Although the new clusters may be moving toward mass concentrations
in the Sloan Great Wall or beyond, many are most likely not yet physically
bound to it.Comment: 21 pages, 9 figures, includes the full appendix table. Accepted for
publication in MNRA
Diffuse steep-spectrum sources from the 74 MHz VLSS survey
Galaxy clusters grow by a sequence of mergers with other clusters and galaxy
groups. During these mergers, shocks and/or turbulence are created within the
intracluster medium (ICM). In this process, particles could be accelerated to
highly relativistic energies. The synchrotron radiation from these particles is
observed in the form of radio relics and halos that are generally characterized
by a steep radio spectral index. Shocks can also revive fossil radio plasma
from a previous episode of AGN activity, creating a so-called radio phoenix.
Here we present multi-frequency radio observations of diffuse steep-spectrum
radio sources selected from the 74 MHz VLSS survey. Previous GMRT observations
showed that some of these sources had filamentary and elongated morphologies,
which are expected for radio relics.
We carried out radio continuum observations at 325 MHz with the GMRT.
Observations with the VLA and WSRT were taken at 1.4 GHz in full polarization
mode. Optical images around the radio sources were taken with the WHT and INT
telescopes. Most of the sources in our sample consist of old radio plasma from
AGNs located in small galaxy clusters. The sources can be classified as AGN
relics or radio phoenices. The spectral indices across most of the radio
sources display large variations. We conclude that diffuse steep-spectrum radio
sources are not only found in massive X-ray luminous galaxy clusters but also
in smaller systems. Future low-frequency surveys will uncover large numbers of
steep-spectrum radio relics related to previous episodes of AGN activity.
[abridged]Comment: 15 pages, 15 figures, accepted for publication in A&A on December 9,
201
Environmental Dependence of Local Luminous Infrared Galaxies
We study the environmental dependence of local luminous infrared galaxies
(LIRGs) and ultraluminous infrared galaxies (ULIRGs) found in the Sloan Digital
Sky Survey (SDSS) data. The LIRG and ULIRG samples are constructed by
cross-correlating spectroscopic catalogs of galaxies of the SDSS Data Release 7
and the Infrared Astronomical Satellite Faint Source Catalog. We examine the
effects of the large-scale background density (Sigma_5), galaxy clusters, and
the nearest neighbor galaxy on the properties of infrared galaxies (IRGs). We
find that the fraction of LIRGs plus ULIRGs among IRGs (f_(U)LIRGs) and the
infrared luminosity (L_IR) of IRGs strongly depend on the morphology of and the
distance to the nearest neighbor galaxy: the probability for an IRG to be a
(U)LIRG (f_(U)LIRGs) and its L_IR both increase as it approaches a late-type
galaxy, but decrease as it approaches an early-type galaxy (within half the
virial radius of its neighbor). We find no dependence of f_(U)LIRGs on the
background density (surface galaxy number density) at fixed stellar mass of
galaxies. The dependence of f_(U)LIRGs on the distance to galaxy clusters is
also found to be very weak, but in highest-density regions such as the center
of galaxy clusters, few (U)LIRGs are found. These environmental dependence of
LIRGs and ULIRGs and the evolution of star formation rate (SFR)-environment
relation from high redshifts to low redshifts seem to support the idea that
galaxy-galaxy interactions/merging play a critical role in triggering the star
formation activity of LIRGs and ULIRGs.Comment: 14 pages, 17 figures. To appear in A&A. Paper with high resolution
figures is available at
http://astro.kias.re.kr/~hshwang/doc/ms_hwang_lirg.pd
The 2MASS Redshift Survey - Description and Data Release
We present the results of the 2MASS Redshift Survey (2MRS), a ten-year
project to map the full three-dimensional distribution of galaxies in the
nearby Universe. The 2 Micron All-Sky Survey (2MASS) was completed in 2003 and
its final data products, including an extended source catalog (XSC), are
available on-line. The 2MASS XSC contains nearly a million galaxies with Ks <=
13.5 mag and is essentially complete and mostly unaffected by interstellar
extinction and stellar confusion down to a galactic latitude of |b|=5 deg for
bright galaxies. Near-infrared wavelengths are sensitive to the old stellar
populations that dominate galaxy masses, making 2MASS an excellent starting
point to study the distribution of matter in the nearby Universe.
We selected a sample of 44,599 2MASS galaxies with Ks =5
deg (>= 8 deg towards the Galactic bulge) as the input catalog for our survey.
We obtained spectroscopic observations for 11,000 galaxies and used
previously-obtained velocities for the remainder of the sample to generate a
redshift catalog that is 97.6% complete to well-defined limits and covers 91%
of the sky. This provides an unprecedented census of galaxy (baryonic mass)
concentrations within 300 Mpc.
Earlier versions of our survey have been used in a number of publications
that have studied the bulk motion of the Local Group, mapped the density and
peculiar velocity fields out to 50 Mpc, detected galaxy groups, and estimated
the values of several cosmological parameters.
Additionally, we present morphological types for a nearly-complete sub-sample
of 20,860 galaxies with Ks = 10 deg.Comment: Accepted for publication in The Astrophysical Journal Supplement
Series. The 2MRS catalogs and a version of the paper with higher-resolution
figures can be found at http://tdc-www.harvard.edu/2mrs
NC ball maps and changes of variables
In this dissertation, we analyze problems set in a dimension-free, noncommutative setting. To be more specific, we use a class of functions defined by power series in noncommutative variables and evaluate these functions on sets of matrices of all sizes - hence the dimension-free term. These types of functions have recently been used in the study of dimension-free linear system engineering problems [HP07], [CHSY03]. Here we analyze a class of functions called NC analytic with the intention of understanding changes of variables in dimension-free classes of problems in matrix variables. To this end, we force geometric constraints on our analytic functions and ask how this affects the algebraic structure of the series defining them. In particular, we present a characterization of maps that send dimension-free matrix balls to dimension-free matrix balls and carry the boundary to the boundary. We study this problem in various cases restricting the variables (and matrices) to have additional symmetric structure and in cases where the variables (and matrices) have no such restrictions. These characterizations are then used to study the more general question of understanding when a dimension-free set is bianalytic to a dimension-free ball. In addition to our study of NC analytic functions, we present a result on a representation of noncommutative rational expressions. Recently there have been studies linking convexity of noncommutative rational functions to linear matrix inequalities, LMIs [HMV06]. The algorithm presented in the final chapter of the thesis presents a necessary step to automatically converting inequalities involving convex rational expressions into LMI
Noncommutative ball maps
Abstract. In this paper, we analyze problems involving matrix variables for which we use a noncommutative algebra setting. To be more specific, we use a class of functions (called NC analytic functions) defined by power series in noncommuting variables and evaluate these functions on sets of matrices of all dimensions; we call such situations dimension-free. These types of functions have recently been used in the study of dimension-free linear system engineering problems [HMPV], [OHMP]. In this paper we characterize NC analytic maps that send dimension-free matrix balls to dimensionfree matrix balls and carry the boundary to the boundary; such maps we call ”NC ball maps”. We find that up to normalization, an NC ball map is the direct sum of the identity map with an NC analytic map of the ball into the ball. That is, “NC ball maps ” are very simple, in contrast to the classical result of D’Angelo on such analytic maps in C. Another mathematically natural class of maps carries a variant of the noncommutative distinguished boundary to the boundary, but on these our results are limited. We shall be interested in several types of noncommutative balls, conventional ones, but also balls defined by constraints called Linear Matrix Inequalities (LMI). What we do here is a small piece of the bigger puzzle of understanding how LMIs behave with respect to noncommutative change of variables. 1