445 research outputs found
The Motions of Clusters of Galaxies and the Dipoles of the Peculiar Velocity Field
In preceding papers of this series, TF relations for galaxies in 24 clusters
with radial velocities between 1000 and 9200 km/s (SCI sample) were obtained, a
Tully-Fisher (TF) template relation was constructed and mean offsets of each
cluster with respect to the template obtained. Here, an estimate of the
line-of-sight peculiar velocities of the clusters and their associated errors
are given. It is found that cluster peculiar velocities in the Cosmic Microwave
Background reference frame do not exceed 600 k/ms and that their distribution
has a line-of-sight dispersion of 300 k/ms, suggesting a more quiescent cluster
peculiar velocity field than previously reported. When measured in a reference
frame in which the Local Group is at rest, the set of clusters at cz > 3000
km/s exhibits a dipole moment in agreement with that of the CMB, both in
amplitude and apex direction. It is estimated that the bulk flow of a sphere of
6000 km/s radius in the CMB reference frame is between 140 and 320 km/s. These
results are in agreement with those obtained from an independent sample of
field galaxies (Giovanelli et al. 1998; see astro-ph/9807274)Comment: 9 pages, 2 tables, 7 figures, uses AAS LaTex; to appear in A
The Correlation Between Galaxy HI Linewidths and K' Luminosities
The relationship between galaxy luminosities and rotation rates is studied
with total luminosities in the K' band. Extinction problems are essentially
eliminated at this band centered at 2.1 micron. A template luminosity-linewidth
relation is derived based on 65 galaxies drawn from two magnitude-limited
cluster samples. The zero-point is determined using 4 galaxies with accurately
known distances. The calibration is applied to give the distance to the Pisces
Cluster (60 Mpc) at a redshift in the CMB frame of 4771 km/s. The resultant
value of the Hubble Constant is 81 km/s/Mpc. The largest sources of uncertainty
arises from the small number of zero-point calibrators at this time at K' and
present application to only one cluster.Comment: 13 pages including 5 figures and 2 tables. Accepted for publication
in Astrophysical Journa
The Clustering of Extragalactic Extremely Red Objects
We have measured the angular and spatial clustering of 671 K5
Extremely Red Objects (EROs) from a 0.98 square degree sub-region of the NOAO
Deep Wide-Field Survey (NDWFS). Our study covers nearly 5 times the area and
has twice the sample size of any previous ERO clustering study. The wide field
of view and BwRIK passbands of the NDWFS allow us to place improved constraints
on the clustering of z=1 EROs. We find the angular clustering of EROs is
slightly weaker than in previous measurements, and w(1')=0.25+/-0.05 for
K<18.40 EROs. We find no significant correlation of ERO spatial clustering with
redshift, apparent color or absolute magnitude, although given the
uncertainties, such correlations remain plausible. We find the spatial
clustering of K5 EROs is well approximated by a power-law, with
r_0=9.7+/-1.1 Mpc/h in comoving coordinates. This is comparable to the
clustering of 4L* early-type galaxies at z<1, and is consistent with the
brightest EROs being the progenitors of the most massive ellipticals. There is
evidence of the angular clustering of EROs decreasing with increasing apparent
magnitude, when NDWFS measurements of ERO clustering are combined with those
from the literature. Unless the redshift distribution of K>20 EROs is very
broad, the spatial clustering of EROs decreases from r_0=9.7+/-1.1 Mpc/h for
K20 EROs.Comment: Accepted for publication in the ApJ. 29 pages with 10 figures. The
NOAO Deep Wide-Field Survey Bootes data release is available online at
http://www.noao.edu/noao/noaodeep
Random Matrix Theory and the Sixth Painlev\'e Equation
A feature of certain ensembles of random matrices is that the corresponding
measure is invariant under conjugation by unitary matrices. Study of such
ensembles realised by matrices with Gaussian entries leads to statistical
quantities related to the eigenspectrum, such as the distribution of the
largest eigenvalue, which can be expressed as multidimensional integrals or
equivalently as determinants. These distributions are well known to be
-functions for Painlev\'e systems, allowing for the former to be
characterised as the solution of certain nonlinear equations. We consider the
random matrix ensembles for which the nonlinear equation is the form
of \PVI. Known results are reviewed, as is their implication by way of series
expansions for the distributions. New results are given for the boundary
conditions in the neighbourhood of the fixed singularities at of
\PVI displayed by a generalisation of the generating function for the
distributions. The structure of these expansions is related to Jimbo's general
expansions for the -function of \PVI in the neighbourhood of its
fixed singularities, and this theory is itself put in its context of the linear
isomonodromy problem relating to \PVI.Comment: Dedicated to the centenary of the publication of the Painlev\'e VI
equation in the Comptes Rendus de l'Academie des Sciences de Paris by Richard
Fuchs in 190
A Complete Catalog of Swift GRB Spectra and Durations: Demise of a Physical Origin for Pre-Swift High-Energy Correlations
We calculate durations and spectral paramaters for 218 Swift bursts detected
by the BAT instrument between and including GRBs 041220 and 070509, including
77 events with measured redshifts. Incorporating prior knowledge into the
spectral fits, we are able to measure the characteristic spectral
peak energy and the isotropic equivalent energy
(1-- keV) for all events. This complete and rather extensive catalog,
analyzed with a unified methodology, allows us to address the persistence and
origin of high-energy correlations suggested in pre-Swift observations. We find
that the - correlation is present in the Swift
sample; however, the best-fit powerlaw relation is inconsistent with the
best-fit pre-Swift relation at >5 sigma significance. Moreover, it has a factor
>~ 2 larger intrinsic scatter, after accounting for large errors on . A large fraction of the Swift events are hard and subluminous
relative to (and inconsistent with) the pre-Swift relation, in agreement with
indications from BATSE GRBs without redshift. Moreover, we determine an
experimental threshold for the BAT detector and show how the -- correlation arises artificially due to partial
correlation with the threshold. We show that pre-Swift correlations found by
Amati et al.(2002), Yonetoku et al. (2004), Firmani et al.(2006) (and
independently by others) are likely unrelated to the physical properties of
GRBs and are likely useless for tests of cosmology. Also, an explanation of
these correlations in terms of a detector threshold provides a natural and
quantitative explanation for why short-duration GRBs and events at low redshift
tend to be outliers to the correlations.Comment: 25 pages, 9 figures, 2 tables, Accepted to Ap
Biases in Virial Black Hole Masses: An SDSS Perspective
We compile black hole (BH) masses for quasars in the redshift
range included in the Fifth Data Release of the
Sloan Digital Sky Survey (SDSS), using virial BH mass estimators based on the
\hbeta, \MgII, and \CIV emission lines. We find that: (1) within our sample,
the widths of the three lines follow log-normal distributions, with means and
dispersions that do not depend strongly on luminosity or redshift;(2) the
\MgII- and \hbeta-estimated BH masses are consistent with one another; and (3)
the \CIV BH mass estimator may be more severely affected by a disk wind
component than the \MgII and \hbeta estimators, giving a positive bias in mass
correlated with the \CIV-\MgII blueshift. Most SDSS quasars have virial BH
masses in the range . There is a clear upper mass limit of
for active BHs at , decreasing at lower
redshifts. Making the reasonable assumptions that the underlying BH mass
distribution decreases with mass and that the Eddington ratio distribution at
fixed BH mass has non-zero width, we show that the measured virial BH mass
distribution and Eddington ratio distribution are subject to Malmquist bias. A
radio quasar subsample (with ) has mean virial BH
mass larger by dex than the whole sample. A broad absorption line
(BAL) quasar subsample (with ) has identical virial
mass distribution as the nonBAL sample, with no mean offset. (Abridged)Comment: Updated virial mass measurements; improved presentation of the MC
simulation; added new discussion sections; conclusions unchanged. The full
table1 is available at
http://www.astro.princeton.edu/~yshen/BH_mass/datafile1.txt.tar.g
Painleve equations from Darboux chains - Part 1: P3-P5
We show that the Painleve equations P3-P5 can be derived (in a unified way)
from a periodic sequence of Darboux transformations for a Schrodinger problem
with quadratic eigenvalue dependency. The general problem naturally divides
into three different branches, each described by an infinite chain of
equations. The Painleve equations are obtained by closing the chain
periodically at the lowest nontrivial level(s). The chains provide ``symmetric
forms'' for the Painleve equations, from which Hirota bilinear forms and Lax
pairs are derived. In this paper (Part 1) we analyze in detail the cases P3-P5,
while P6 will be studied in Part 2.Comment: 23 pages, 1 reference added + minor change
Treading Water: Tools to Help US Coastal Communities Plan for Sea Level Rise Impacts
As communities grapple with rising seas and more frequent flooding events, they need improved projections of future rising and flooding over multiple time horizons, to assist in a multitude of planning efforts. There are currently a few different tools available that communities can use to plan, including the Sea Level Report Card and products generated by a United States. Federal interagency task force on sea level rise. These tools are a start, but it is recognized that they are not necessarily enough at present to provide communities with the type of information needed to support decisions that range from seasonal to decadal in nature, generally over relatively small geographic regions. The largest need seems to come from integrated models and tools. Agencies need to work with communities to develop tools that integrate several aspects (rainfall, tides, etc.) that affect their coastal flooding problems. They also need a formalized relationship with end users that allows agency products to be responsive to the various needs of managers and decision makers. Existing boundary organizations can be leveraged to meet this need. Focusing on addressing these needs will allow agencies to create robust solutions to flood risks, leading to truly resilient communities
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