990 research outputs found
The Evolution of the Galaxy Cluster Luminosity-Temperature Relation
We analyzed the luminosity-temperature (L-T) relation for 2 samples of galaxy
clusters which have all been observed by the ASCA satellite. We used 32 high
redshift clusters (0.3<z<0.6), 53 low redshift clusters (z<0.3), and also the
combination of the low and high redshift datasets. We assumed a power law
relation between the bolometric luminosity of the galaxy cluster and its
integrated temperature and redshift (L_{bol,44}=C*T^alpha*(1+z)^A). The results
are consistent, independent of cosmology, with previous estimates of
LT found by other authors. We observed weak or zero evolution.Comment: 20 pages, Latex, 11 figures, GIF forma
Weak lensing observations of the "dark" cluster MG2016+112
We investigate the possible existence of a high-redshift (z=1) cluster of
galaxies associated with the QSO lens system MG2016+112. From an ultra-deep R-
and less deep V- and I-band Keck images and a K-band mosaic from UKIRT, we
detect ten galaxies with colors consistent with the lensing galaxy within
225h^{-1} kpc of the z=1.01 lensing galaxy. This represents an overdensity of
more than ten times the number density of galaxies with similar colors in the
rest of the image. We also find a group of seven much fainter objects closely
packed in a group only 27h^{-1} kpc north-west of the lensing galaxy. We
perform a weak lensing analysis on faint galaxies in the R-band image and
detect a mass peak of a size similar to the mass inferred from X-ray
observations of the field, but located 64" northwest of the lensing galaxy.
From the weak lensing data we rule out a similar sized mass peak centered on
the lensing galaxy at the 2 sigma level.Comment: 9 pages, 10 figures, submitted to A&A version with figure 4 at higher
resolution can be downloaded from
http://www.mpa-garching.mpg.de/~clowe/mg2016aa.ps.g
Evolution of the Cluster X-ray Luminosity Function
We report measurements of the cluster X-ray luminosity function out to z=0.8
based on the final sample of 201 galaxy systems from the 160 Square Degree
ROSAT Cluster Survey. There is little evidence for any measurable change in
cluster abundance out to z~0.6 at luminosities less than a few times 10^44
ergs/s (0.5-2.0 keV). However, between 0.6 < z < 0.8 and at luminosities above
10^44 ergs/s, the observed volume densities are significantly lower than those
of the present-day population. We quantify this cluster deficit using
integrated number counts and a maximum-likelihood analysis of the observed
luminosity-redshift distribution fit with a model luminosity function. The
negative evolution signal is >3 sigma regardless of the adopted local
luminosity function or cosmological framework. Our results and those from
several other surveys independently confirm the presence of evolution. Whereas
the bulk of the cluster population does not evolve, the most luminous and
presumably most massive structures evolve appreciably between z=0.8 and the
present. Interpreted in the context of hierarchical structure formation, we are
probing sufficiently large mass aggregations at sufficiently early times in
cosmological history where the Universe has yet to assemble these clusters to
present-day volume densities.Comment: 15 pages, 10 figures, accepted for publication in Ap
The Politics of Paying for Health Reform: Zombies, Payroll Taxes, and the Holy Grail
Outlines the political and institutional contexts for efforts to finance universal health coverage. Analyzes the political feasibility and consequences of various funding options and their implications for cost control. Includes international comparisons
Cluster Evolution in the ROSAT North Ecliptic Pole Survey
The deepest region of the ROSAT All-Sky Survey, at the North Ecliptic Pole,
has been studied to produce a complete and unbiased X-ray selected sample of
clusters of galaxies. This sample is used to investigate the nature of cluster
evolution and explore potential implications for large-scale structure models.
The survey is 99.6% optically identified. Spectroscopic redshifts have been
measured for all the extragalactic identifications. In this Letter, first
results on cluster evolution are presented based on a comparison between the
number of the observed clusters in the North Ecliptic Pole survey and the
number of expected clusters assuming no-evolution models. At z>0.3 there is a
deficit of clusters with respect to the local universe which is significant at
> 4.7sigma. The evolution appears to commence at L_{0.5-2.0} > 1.8x10^{44} erg
s^{-1} in our data. The negative evolution goes in the same direction as the
original EMSS result, the results from the 160 deg^{2} survey by Vikhlinin et
al. (1998) and the recent results from the RDCS (Rosati et al. 2000). At lower
redshifts there is no evidence for evolution, a result in agreement with these
and other cluster surveys.Comment: 17 pages, 3 figures. Accepted for publication in ApJ Letter
The X-ray Cluster Normalization of the Matter Power Spectrum
The number density of galaxy clusters provides tight statistical constraints
on the matter fluctuation power spectrum normalization, traditionally phrased
in terms of sigma_8, the root mean square mass fluctuation in spheres with
radius 8 h^-1 Mpc. We present constraints on sigma_8 and the total matter
density Omega_m0 from local cluster counts as a function of X-ray temperature,
taking care to incorporate and minimize systematic errors that plagued previous
work with this method. In particular, we present new determinations of the
cluster luminosity - temperature and mass - temperature relations, including
their intrinsic scatter, and a determination of the Jenkins mass function
parameters for the same mass definition as the mass - temperature calibration.
Marginalizing over the 12 uninteresting parameters associated with this method,
we find that the local cluster temperature function implies sigma_8
(Omega_m0/0.32)^alpha = 0.86+/-0.04 with alpha = 0.30 (0.41) for Omega_m0 <
0.32 (Omega_mo > 0.32) (68% confidence for two parameters). This result agrees
with a wide range of recent independent determinations, and we find no evidence
of any additional sources of systematic error for the X-ray cluster temperature
function determination of the matter power spectrum normalization. The joint
WMAP5 + cluster constraints are: Omega_m0 = 0.30+0.03/-0.02 and sigma_8 =
0.85+0.04/-0.02 (68% confidence for two parameters).Comment: 31 pages, 16 figures, accept for publication in ApJ 609, Jan. 10,
200
A Map of the Universe
We have produced a new conformal map of the universe illustrating recent
discoveries, ranging from Kuiper belt objects in the Solar system, to the
galaxies and quasars from the Sloan Digital Sky Survey. This map projection,
based on the logarithm map of the complex plane, preserves shapes locally, and
yet is able to display the entire range of astronomical scales from the Earth's
neighborhood to the cosmic microwave background. The conformal nature of the
projection, preserving shapes locally, may be of particular use for analyzing
large scale structure. Prominent in the map is a Sloan Great Wall of galaxies
1.37 billion light years long, 80% longer than the Great Wall discovered by
Geller and Huchra and therefore the largest observed structure in the universe.Comment: Figure 8, and additional material accessible on the web at:
http://www.astro.princeton.edu/~mjuric/universe
Observational Constraints on the Catastrophic Disruption Rate of Small Main Belt Asteroids
We have calculated 90% confidence limits on the steady-state rate of
catastrophic disruptions of main belt asteroids in terms of the absolute
magnitude at which one catastrophic disruption occurs per year (HCL) as a
function of the post-disruption increase in brightness (delta m) and subsequent
brightness decay rate (tau). The confidence limits were calculated using the
brightest unknown main belt asteroid (V = 18.5) detected with the Pan-STARRS1
(Pan-STARRS1) telescope. We measured the Pan-STARRS1's catastrophic disruption
detection efficiency over a 453-day interval using the Pan-STARRS moving object
processing system (MOPS) and a simple model for the catastrophic disruption
event's photometric behavior in a small aperture centered on the catastrophic
disruption event. Our simplistic catastrophic disruption model suggests that
delta m = 20 mag and 0.01 mag d-1 < tau < 0.1 mag d-1 which would imply that H0
= 28 -- strongly inconsistent with H0,B2005 = 23.26 +/- 0.02 predicted by
Bottke et al. (2005) using purely collisional models. We postulate that the
solution to the discrepancy is that > 99% of main belt catastrophic disruptions
in the size range to which this study was sensitive (100 m) are not
impact-generated, but are instead due to fainter rotational breakups, of which
the recent discoveries of disrupted asteroids P/2013 P5 and P/2013 R3 are
probable examples. We estimate that current and upcoming asteroid surveys may
discover up to 10 catastrophic disruptions/year brighter than V = 18.5.Comment: 61 Pages, 10 Figures, 3 Table
- …