427 research outputs found
Luminosity density estimation from redshift surveys and the mass density of the Universe
In most direct estimates of the mass density (visible or dark) of the
Universe, a central input parameter is the luminosity density of the Universe.
Here we consider the measurement of this luminosity density from red-shift
surveys, as a function of the yet undetermined characteristic scale R_H at
which the spatial distribution of visible matter tends to a well defined
homogeneity. Making the canonical assumption that the cluster mass to
luminosity ratio M/L is the universal one, we can estimate the total mass
density as a function \Omega_m(R_H,M/L). Taking the highest estimated cluster
value M/L ~300h and a conservative lower limit R_H > 20 Mpc/h, we obtain the
upper bound \Omega_m < 0.1 . We note that for values of the homogeneity scale
R_H in the range R_H ~ (90 +/- 45) hMpc, the value of \Omega_m may be
compatible with the nucleosynthesis inferred density in baryons.Comment: 16 pages, latex, no figures. To be published in Astrophysical Journal
Letter
SWASHES: a compilation of Shallow Water Analytic Solutions for Hydraulic and Environmental Studies
Numerous codes are being developed to solve Shallow Water equations. Because
there are used in hydraulic and environmental studies, their capability to
simulate properly flow dynamics is critical to guarantee infrastructure and
human safety. While validating these codes is an important issue, code
validations are currently restricted because analytic solutions to the Shallow
Water equations are rare and have been published on an individual basis over a
period of more than five decades. This article aims at making analytic
solutions to the Shallow Water equations easily available to code developers
and users. It compiles a significant number of analytic solutions to the
Shallow Water equations that are currently scattered through the literature of
various scientific disciplines. The analytic solutions are described in a
unified formalism to make a consistent set of test cases. These analytic
solutions encompass a wide variety of flow conditions (supercritical,
subcritical, shock, etc.), in 1 or 2 space dimensions, with or without rain and
soil friction, for transitory flow or steady state. The corresponding source
codes are made available to the community
(http://www.univ-orleans.fr/mapmo/soft/SWASHES), so that users of Shallow
Water-based models can easily find an adaptable benchmark library to validate
their numerical methods.Comment: 40 pages There are some errors in the published version. This is a
corrected versio
The intermediate-redshift galaxy cluster CL 0048-2942. Stellar populations
We present a detailed study of the cluster CL 0048-2942, located at z~0.64,
based on a photometric and spectroscopic catalogue of 54 galaxies in a 5 x 5
square arcmin region centred in that cluster. Of these, 23 galaxies were found
to belong to the cluster. Based on this sample, the line-of-sight velocity
dispersion of the cluster is approximately 680 +- 140 km/s. We have performed
stellar population synthesis in the cluster members as well as in the field
galaxies of the sample and found that there are population gradients in the
cluster with central galaxies hosting mainly intermediate/old populations
whereas galaxies in the cluster outskirts show clearly an increase of younger
populations, meaning that star formation is predominantly taking place in the
outer regions of the cluster. In a general way, field galaxies seem to host
less evolved stellar populations than cluster members. In fact, in terms of
ages, young supergiant stars dominate the spectra of field galaxies whereas
cluster galaxies display a dominant number of old and intermediate age stars.
Following the work of other authors (e.g. Dressler et al. 1999) we have
estimated the percentage of K+A galaxies in our sample and found around 13% in
the cluster and 10% in the field. These values were estimated through means of
a new method, based on stellar population synthesis results, that takes into
account all possible absorption features in the spectrum and thus makes optimal
use of the data.Comment: Accepted by Astronomy & Astrophysics. 24 pages, 10 figures, 10 tables
(figures 3, 4, 5 and tables 1, 3, 4, 5, 6, 7, 8 will be available in
electronic format only in the A&A published version
A VLT spectroscopic survey of RX J0152.7-1357, a forming cluster of galaxies at z=0.837
We present the results of an extensive spectroscopic survey of RX
J0152.7-1357, one of the most massive distant clusters of galaxies known.
Multi-object spectroscopy, carried out with FORS1 and FORS2 on the ESO Very
Large Telescope (VLT), has allowed us to measure more than 200 redshifts in the
cluster field and to confirm 102 galaxies as cluster members. The mean redshift
of the cluster is and we estimate the velocity dispersion
of the overall cluster galaxy distribution to be $\sim 1600 \mathrm{km \
s^{-1}}\sim919\sim737 \mathrm{km s^{-1}}\lambda$3727) emission lines is
observed in the outskirts of the cluster. Two AGNs, which were previously
confused with the diffuse X-ray emission from the intracluster medium in ROSAT
and BeppoSAX observations, are found to be cluster members.Comment: 16 pages. 13 figures. Accepted for publication in Astronomy &
Astrophysics. Tables 4 and 5 available in printed version. Corrected typos
and missing reference
HST large field weak lensing analysis of MS 2053-04: study of the mass distribution and mass-to-light ratio of X-ray selected clusters at 0.22<z<0.83
We have detected the weak lensing signal induced by the cluster of galaxies
MS 2053-04 (z=0.58) from a two-colour mosaic of 6 HST WFPC2 images. The best
fit singular isothermal sphere model to the observed tangential distortion
yields an Einstein radius r_E=6.2"+-1.8", which corresponds to a velocity
dispersion of 886^{+121}_{-139} km/s. This result is in good agreement with the
observed velocity dispersion of 817+-80 km/s from cluster members.
MS 2053 is the third cluster we studied using mosaics of deep WFPC2 images.
For all three clusters we find good agreement between dynamical and weak
lensing velocity dispersions, in contrast to weak lensing studies based on
single WFPC2 pointings on cluster cores. This result demonstrates the
importance of wide field data. We have compared the ensemble averaged cluster
profile to the predicted NFW profile, and find that a NFW profile can fit the
observed lensing signal well. The best fit concentration parameter is found to
be 0.79^{+0.44}_{-0.15} (68% confidence) times the predicted value from an open
CDM model. The observed mass-to-light ratios of the clusters in our sample
evolve with redshift, and are inconsistent with a constant, non-evolving,
mass-to-light ratio at the 99% confidence level. The evolution is consistent
with the results derived from the evolution of the fundamental plane of early
type galaxies. The resulting average mass-to-light ratio for massive clusters
at z=0 is found to be 239+-18+-9 M/L_B. (abridged)Comment: submitted to MNRAS 12 pages, 13 figure
Spectroscopy of the neighboring massive clusters Abell 222 and Abell 223
We present a spectroscopic catalog of the neighboring massive clusters Abell
222 and Abell 223. The catalog contains the positions, redshifts, R magnitudes,
V-R color, as well as the equivalent widths for a number of lines for 183
galaxies, 153 of them belonging to the A 222 and A 223 system. We determine the
heliocentric redshifts to be z=0.2126+/-0.0008 for A 222 and z=0.2079+/-0.0008
for A 223. The velocity dispersions of both clusters in the cluster restframe
are about the same: sigma = 1014^{+90}_{-71} km/s and sigma = 1032^{+99}_{-76}
km/s for A 222 and A 223, respectively. While we find evidence for substructure
in the spatial distribution of A 223, no kinematic substructure can be
detected. From the red cluster sequence identified in a
color--magnitude--diagram we determine the luminosity of both clusters and
derive mass--to--light ratios in the R--band of (M/L)_A222 = (202+/-43) h_70
M_{su}n/L_{sun} and (M/L)_A223 = (149+/-33) h_70 M_{sun}/L_{sun}. Additionally
we identify a group of background galaxies at z ~ 0.242.Comment: Accepted for publication in A&A, 10 pages, 9 figures, full version of
table 2 included in source distribution, version with higher quality images
available from http://www.astro.uni-bonn.de/~dietrich
China’s Blue Economy: A State Project of Modernisation
The blue economy is a globally emerging concept for ocean governance that seeks to tap the economic potential of the oceans in environmentally sustainable ways. Yet, understanding and implementation of particular visions of the blue economy in specific regions diverge according to national and other contexts. Drawing on a discourse analysis of Chinese language documents, this article assesses how the blue economy has been conceptualised in Chinese state policy and discourse. Part of a state ideology and practice of modernisation that is defined in terms of rejuvenation under a strong state, the blue economy in China is seen as an opportunity to promote modernisation from overlapping economic, geopolitical and ecological perspectives and actions. China’s distinctive model for the blue economy presents emerging challenges for global ocean governance
Projection effects in cluster mass estimates : the case of MS2137
We revisit the mass properties of the lensing cluster of galaxies MS2137-23
and assess the mutual agreement between cluster mass estimates based on
lensing, X-rays and stellar dynamics. We perform a thorough elliptical lens
modelling using arcs in the range 20<R<100kpc and weak lensing (100<R<1000kpc).
We confirm that the dark matter distribution is consistent with an NFW profile
with high concentration . We further analyse the stellar
kinematics data of Sand etal(2004) with a detailed modelling of the los
velocity distribution of stars in the cD galaxy and quantify the small bias due
to non-Gaussianity of the LOSVD. After correction, the NFW lens model is still
unable to properly fit kinematical data and is twice as massive as suggested by
X-rays (Allen etal2001). The discrepancy between projected and tridimensional
mass estimates is studied by assuming prolate (triaxial) halos with the major
axis oriented toward the line-of-sight. This model well explains the high
concentration and the misalignement of 13 deg between stellar and dark matter
components. We then calculate the systematic and statistical uncertainties in
the relative normalization between cylindric M(< R) and spherical M(< r) mass
estimates for triaxial halos. These uncertainties prevent any attempt to couple
2D and 3D constraints without a complete tridimensional analysis. Such
asphericity/projection effects should be a major concern for comparisons
between lensing and X-rays/dynamics mass estimates.Comment: Final accepted version in A&A with Improved discussion and figures.
Full resolution pdf version at
ftp://ftp.iap.fr/pub/from\_users/gavazzi/MS2137\_triax.pd
The Red Sequence Luminosity Function in Massive Intermediate Redshift Galaxy Clusters
We measure the rest-frame B-band luminosity function of red-sequence galaxies
(RSLF) of five intermediate-redshift (0.5 950
km/s) clusters. Cluster galaxies are identified through photometric redshifts
based on imaging in seven bands (five broad, and two narrow) using the WIYN
3.5m telescope. The luminosity functions are well-fit down to M_B^*+3 for all
of the clusters out to a radius of R_200. For comparison, the luminosity
functions for a sample of 59 low redshift clusters selected from the SDSS are
measured as well. There is a brightening trend (M_B^* increases by 0.7 mags by
z=0.75) with redshift comparable to what is seen in the field for similarly
defined galaxies, although there is a hint that the cluster red-sequence
brightening is more rapid in the past (z>0.5), and relatively shallow at more
recent times. Contrary to other claims, we find little evidence for evolution
of the faint end slope. Previous indications of evolution may be due to
limitations in measurement technique, bias in the sample selection, and cluster
to cluster variation. As seen in both the low and high redshift sample, a
significant amount of variation in luminosity functions parameters alpha and
M^* exists between individual clusters.Comment: 40 pages, 14 figures, accepted for publication in the Astrophysical
Journa
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