293 research outputs found
Thirty-fold: Extreme gravitational lensing of a quiescent galaxy at
We report the discovery of eMACSJ1341-QG-1, a quiescent galaxy at
located behind the massive galaxy cluster eMACSJ1341.92442 (). The
system was identified as a gravitationally lensed triple image in Hubble Space
Telescope images obtained as part of a snapshot survey of the most X-ray
luminous galaxy clusters at and spectroscopically confirmed in
ground-based follow-up observations with the ESO/X-Shooter spectrograph. From
the constraints provided by the triple image, we derive a first, crude model of
the mass distribution of the cluster lens, which predicts a gravitational
amplification of a factor of 30 for the primary image and a factor of
6 for the remaining two images of the source, making eMACSJ1341-QG-1 by
far the most strongly amplified quiescent galaxy discovered to date. Our
discovery underlines the power of SNAPshot observations of massive, X-ray
selected galaxy clusters for lensing-assisted studies of faint background
populations
Hayek e Mises:: Dos dias em Viena às ConcepçÔes sobre o Processo de Mercado
This article explains Friedrich A. Hayek and Ludwig von Mises personal and professional relationship during the period between the two World Wars, and explains their conceptions of the market process and the role of knowledge, prices and entrepreneurial expectations in tending to bring about competitive market coordination. Besides, it discusses those areas in which their approaches to these issues were complementary but not the same concerning expectations-formation in the market process.O artigo explica a sua relação pessoal e profissional entre Friedrich A. Hayek e Ludwig von Mises durante o perĂodo entre as duas Guerras Mundiais e, tambĂ©m explica as concepçÔes destes dois economistas sobre processo de mercado, papel do conhecimento, preços e expectativas empreendedoras na tendĂȘncia de produzir coordenação do mercado competitivo. AlĂ©m disso, discute aquelas ĂĄreas nas quais suas abordagens para tais questĂ”es eram complementares, o mesmo nĂŁo acontecendo no que diz respeito Ă formação de expectativas no processo de mercado
Generalized Berry Conjecture and mode correlations in chaotic plates
We consider a modification of the Berry Conjecture for eigenmode statistics
in wave-bearing systems. The eigenmode correlator is conjectured to be
proportional to the imaginary part of the Green's function. The generalization
is applicable not only to scalar waves in the interior of homogeneous isotropic
systems where the correlator is a Bessel function, but to arbitrary points of
heterogeneous systems as well. In view of recent experimental measurements,
expressions for the intensity correlator in chaotic plates are derived.Comment: 5 pages, 1 figur
LoCuSS: First Results from Strong-lensing Analysis of 20 Massive Galaxy Clusters at z~0.2
We present a statistical analysis of a sample of 20 strong lensing clusters
drawn from the Local Cluster Substructure Survey (LoCuSS), based on high
resolution Hubble Space Telescope imaging of the cluster cores and follow-up
spectroscopic observations using the Keck-I telescope. We use detailed
parameterized models of the mass distribution in the cluster cores, to measure
the total cluster mass and fraction of that mass associated with substructures
within R<250kpc.These measurements are compared with the distribution of
baryons in the cores, as traced by the old stellar populations and the X-ray
emitting intracluster medium. Our main results include: (i) the distribution of
Einstein radii is log-normal, with a peak and 1sigma width of
=1.16+/-0.28; (ii) we detect an X-ray/lensing mass discrepancy of
=1.3 at 3 sigma significance -- clusters with larger substructure
fractions displaying greater mass discrepancies, and thus greater departures
from hydrostatic equilibrium; (iii) cluster substructure fraction is also
correlated with the slope of the gas density profile on small scales, implying
a connection between cluster-cluster mergers and gas cooling. Overall our
results are consistent with the view that cluster-cluster mergers play a
prominent role in shaping the properties of cluster cores, in particular
causing departures from hydrostatic equilibrium, and possibly disturbing cool
cores. Our results do not support recent claims that large Einstein radius
clusters present a challenge to the CDM paradigm.Comment: 28 pages, 14 figures, accepted for publication in MNRAS, replaced
with accepted versio
An Empirically-Calibrated Model For Interpreting the Evolution of Galaxies During the Reionization Era
[Abridged] We develop a simple star formation model whose goal is to
interpret the emerging body of observational data on star-forming galaxies at
z>~6. The efficiency and duty cycle of the star formation activity within dark
matter halos are determined by fitting the luminosity functions of Lya emitter
and Lyman-break galaxies at redshifts z~5-6. Using our model parameters we
predict the likely abundance of star forming galaxies at earlier epochs and
compare these to the emerging data in the redshift interval 7<z<10. We find
that the abundance of luminous Lyman-break galaxies in the 500 Myr between z~6
and 10 can be naturally explained by the hierarchical assembly of dark matter
haloes; there is only marginal evidence for strong physical evolution. In
contrast, the first estimates of the abundance of less luminous star forming
galaxies at z=9-10 are higher than predicted and, if verified by further data,
may suggest a top-heavy stellar mass function at these early epochs. Although
these abundances remain uncertain because of the difficulty of spectroscopic
confirmation and cosmic variance, even a modest improvement in survey
capability with present or upcoming facilities should yield great progress. In
this context, we use our model to consider those observational techniques that
hold the most promise and make predictions for specific surveys that are, or
will soon be, underway. We conclude that narrowband Lya emitter surveys should
be efficient on searches at z~7-8; however, such conventional surveys are
unlikely to detect sufficient galaxies at z~10 to provide useful constraints.
For this reason, gravitational lensing offers the best prospect for probing the
z~10 universe prior to JWST.Comment: 17 pages, 12 figures, submitted to Ap
A statistical study of multiply-imaged systems in the lensing cluster Abell 68
We have carried out an extensive spectroscopic survey with the Keck and VLT telescopes, targeting lensed galaxies in the background of the massive cluster Abell 68. Spectroscopic measurements are obtained for 26 lensed images, including a distant galaxy at z=5.4 . Redshifts have been determined for 5 out of 7 multiply-image systems. Through a careful modeling of the mass distribution in the strongly-lensed regime, we derive a mass estimate of 5.3 x 10^14 Msun within 500 kpc. Our mass model is then used to constrain the redshift distribution of the remaining multiply-imaged and singly-imaged sources. This enables us to examine the physical properties for a subsample of 7 Lyman-alpha emitters at 1.7 < z < 5.5, whose unlensed luminosities of ~ 10^41 ergs/s are fainter than similar objects found in blank fields. Of particular interest is an extended Lyman-alpha emission region surrounding a highly magnified source at z=2.6, detected in VIMOS Integral Field Spectroscopy data. The physical scale of the most distant lensed source at z=5.4 is very small (<300 pc), similar to the lensed z ~ 5.6 emitter reported by Ellis et al. (2001) in Abell 2218. New photometric data available for Abell 2218 allow for a direct comparison between these two unique objects. Our survey illustrates the practicality of using lensing clusters to probe the faint end of the z ~ 2-5 Lyman-alpha luminosity function in a manner that is complementary to blank field narrow-band surveys
Hubble Frontier Fields: a high-precision strong-lensing analysis of the massive galaxy cluster Abell 2744 usingâŒ180 multiple images
We present a high-precision mass model of galaxy cluster Abell 2744, based on a strong gravitational-lensing analysis of the Hubble Space Telescope Frontier Fields (HFF) imaging data, which now include both Advanced Camera for Surveys and Wide Field Camera 3 observations to the final depth. Taking advantage of the unprecedented depth of the visible and near-infrared data, we identify 34 new multiply imaged galaxies, bringing the total to 61, comprising 181 individual lensed images. In the process, we correct previous erroneous identifications and positions of multiple systems in the northern part of the cluster core. With the lenstool software and the new sets of multiple images, we model the cluster using two cluster-scale dark matter haloes plus galaxy-scale haloes for the cluster members. Our best-fitting model predicts image positions with an rms error of 0.79arcsec, which constitutes an improvement by almost a factor of 2 over previous parametric models of this cluster. We measure the total projected mass inside a 200kpc aperture as (2.162±0.005) Ă1014âMâ, thus reaching 1âperâcent level precision for the second time, following the recent HFF measurement of MACSJ0416.1â2403. Importantly, the higher quality of the mass model translates into an overall improvement by a factor of 4 of the derived magnification factor. Together with our previous HFF gravitational lensing analysis, this work demonstrates that the HFF data enables high-precision mass measurements for massive galaxy clusters and the derivation of robust magnification maps to probe the early Univers
Sunyaev-Zel'dovich observations of galaxy clusters out to the virial radius with the Arcminute Microkelvin Imager
We present observations using the Small Array of the Arcminute Microkelvin
Imager (AMI; 14-18 GHz) of four Abell and three MACS clusters spanning
0.171-0.686 in redshift. We detect Sunyaev-Zel'dovich (SZ) signals in five of
these without any attempt at source subtraction, although strong source
contamination is present. With radio-source measurements from high-resolution
observations, and under the assumptions of spherical -model,
isothermality and hydrostatic equilibrium, a Bayesian analysis of the data in
the visibility plane detects extended SZ decrements in all seven clusters over
and above receiver noise, radio sources and primary CMB imprints. Bayesian
evidence ratios range from 10^{11}:1 to 10^{43}:1 for six of the clusters and
3000:1 for one with substantially less data than the others. We present
posterior probability distributions for, e.g., total mass and gas fraction
averaged over radii internal to which the mean overdensity is 1000, 500 and
200, r_200 being the virial radius. Reaching r_200 involves some extrapolation
for the nearer clusters but not for the more-distant ones. We find that our
estimates of gas fraction are low (compared with most in the literature) and
decrease with increasing radius. These results appear to be consistent with the
notion that gas temperature in fact falls with distance (away from near the
cluster centre) out to the virial radius.Comment: 18 pages, 10 figures, submitted to MNRAS (updated authors and fixed
Figure 1
Comparison of an X-ray selected sample of massive lensing clusters with the MareNostrum Universe LCDM simulation
A long-standing problem of strong lensing by galaxy clusters regards the
observed high rate of giant gravitational arcs as compared to the predictions
in the framework of the "standard" cosmological model. Recently, few other
inconsistencies between theoretical expectations and observations have been
claimed which regard the large size of the Einstein rings and the high
concentrations of few clusters with strong lensing features. All of these
problems consistently indicate that observed galaxy clusters may be
gravitational lenses stronger than expected. We use clusters extracted from the
MareNostrum Universe to build up mock catalogs of galaxy clusters selected
through their X-ray flux. We use these objects to estimate the probability
distributions of lensing cross sections, Einstein rings, and concentrations for
the sample of 12 MACS clusters at presented in Ebeling et al. (2007)
and discussed in Zitrin et al. (2010). We find that simulated clusters produce
less arcs than observed clusters do. The medians of the
distributions of the Einstein ring sizes differ by between
simulations and observations. We estimate that, due to cluster triaxiality and
orientation biases affecting the lenses with the largest cross sections, the
concentrations of the individual MACS clusters inferred from the lensing
analysis should be up to a factor of larger than expected from the
CDM model. The arc statistics, the Einstein ring, and the
concentration problems in strong lensing clusters are mitigated but not solved
on the basis of our analysis. Nevertheless, due to the lack of redshifts for
most of the multiple image systems used for modeling the MACS clusters, the
results of this work will need to be verified with additional data. The
upcoming CLASH program will provide an ideal sample for extending our
comparison (abridged).Comment: 11 pages, 9 figures, accepted for publication on A&
Hubble Frontier Fields: a high-precision strong-lensing analysis of galaxy cluster MACSJ0416.1-2403 usingâŒ200 multiple images
We present a high-precision mass model of the galaxy cluster MACSJ0416.1-2403, based on a strong-gravitational-lensing analysis of the recently acquired Hubble Space Telescope Frontier Fields (HFF) imaging data. Taking advantage of the unprecedented depth provided by HST/Advanced Camera for Survey observations in three passbands, we identify 51 new multiply imaged galaxies, quadrupling the previous census and bringing the grand total to 68, comprising 194 individual lensed images. Having selected a subset of the 57 most securely identified multiply imaged galaxies, we use the lenstool software package to constrain a lens model comprised of two cluster-scale dark-matter haloes and 98 galaxy-scale haloes. Our best-fitting model predicts image positions with an rms error of 0.68arcsec, which constitutes an improvement of almost a factor of 2 over previous, pre-HFF models of this cluster. We find the total projected mass inside a 200kpc aperture to be (1.60±0.01)Ă1014âMâ, a measurement that offers a three-fold improvement in precision, reaching the per cent level for the first time in any cluster. Finally, we quantify the increase in precision of the derived gravitational magnification of high-redshift galaxies and find an improvement by a factor ofâŒ2.5 in the statistical uncertainty. Our findings impressively confirm that HFF imaging has indeed opened the domain of high-precision mass measurements for massive clusters of galaxie
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