1,221 research outputs found
Mapping Cluster Mass Distributions via Gravitational Lensing of Background Galaxies
We present a new method for measuring the projected mass distributions of
galaxy clusters. The gravitational amplification is measured by comparing the
joint distribution in redshift and magnitude of galaxies behind the cluster
with that of field galaxies. We show that the total amplification is directly
related to the surface mass density in the weak field limit, and so it is
possible to map the mass distribution of the cluster. The method is shown to be
limited by discreteness noise and galaxy clustering behind the lens. Galaxy
clustering sets a lower limit to the error along the redshift direction, but a
clustering independent lensing signature may be obtained from the magnitude
distribution at fixed redshift. Statistical techniques are developed for
estimating the surface mass density of the cluster. We extend these methods to
account for any obscuration by cluster halo dust, which may be mapped
independently of the dark matter. We apply the method to a series of numerical
simulations and show the feasibility of the approach. We consider approximate
redshift information, and show how the mass estimates are degraded.Comment: ApJ in press. 23 pages of LaTeX plus figs. Text & figs available by
anonymous ftp from resun03.roe.ac.uk in directory /pub/jap/lens (you need
btp.tex and apj.sty
Transcendental numbers and the topology of three-loop bubbles
We present a proof that all transcendental numbers that are needed for the
calculation of the master integrals for three-loop vacuum Feynman diagrams can
be obtained by calculating diagrams with an even simpler topology, the topology
of spectacles.Comment: 4 pages in REVTeX, 1 PostScript figure included, submitted to Phys.
Rev. Let
Free Form Lensing Implications for the Collision of Dark Matter and Gas in the Frontier Fields Cluster MACSJ0416.1-2403
We present a free form mass reconstruction of the massive lensing cluster
MACSJ0416.1-2403 using the latest Hubble Frontier Fields data. Our model
independent method finds that the extended lensing pattern is generated by two
elongated, closely projected clusters of similar mass. Our lens model
identifies new lensed images with which we improve the accuracy of the dark
matter distribution. We find that the bimodal mass distribution is nearly
coincident with the bimodal X-ray emission, but with the two dark matter peaks
lying closer together than the centroids of the X-ray emisison. We show this
can be achieved if the collision has occurred close to the plane and such that
the cores are deflected around each other. The projected mass profiles of both
clusters are well constrained because of the many interior lensed images,
leading to surprisingly flat mass profiles of both components in the region
15-100 kpc. We discuss the extent to which this may be generated by tidal
forces in our dynamical model which are large during an encounter of this type
as the cores "graze" each other. The relative velocity between the two cores is
estimated to be about 1200 km/s and mostly along the line of sight so that our
model is consistent with the relative redshift difference between the two cD
galaxies (dz = 0.04).Comment: 22 pages, 18 figures, 2 table
A faint galaxy redshift survey to B=24
Using the multislit LDSS-2 spectrograph on the {\it William Herschel
Telescope} we have completed a redshift survey in the magnitude range which has produced 73 redshifts representing a 73\% complete sample
uniformly-selected from four deep fields at high Galactic latitude. The survey
extends out to and includes the highest redshift galaxy () yet
discovered in a field sample. The median redshift, \zmed=0.46, and form of
the redshift distribution constitute compelling evidence against simple
luminosity evolution as an explanation of the large excess of faint galaxies
(2--4 no-evolution) seen in this magnitude range. Rather we
identify the excess population as blue objects with and \,
luminosities similar to local galaxies indicating a dramatic decrease in
the density of such objects over the last Hubble time, confirming the trends
found in brighter redshift surveys. We also find a marked absence of {\it very}
low redshift galaxies (0.1) at faint limits, severely constraining any
significant steepening of the local field galaxy luminosity function at low
luminosities.Comment: uuencoded compressed postscript. The preprint are also available at
URL http://www.ast.cam.ac.uk/preprint/PrePrint.htm
The nature of power corrections in large approximation
We investigate the nature of power corrections and infrared renormalon
singularities in large approximation. We argue that the power
correction associated with a renormalon pole singularity should appear at O(1),
in contrast to the renormalon ambiguity appearing at , and give
an explanation why the leading order renormalon singularities are generically
poles.Comment: 6 page
Non-parametric mass reconstruction of A1689 from strong lensing data with SLAP
We present the mass distribution in the central area of the cluster A1689 by
fitting over 100 multiply lensed images with the non-parametric Strong Lensing
Analysis Package (SLAP, Diego et al. 2004). The surface mass distribution is
obtained in a robust way finding a total mass of 0.25E15 M_sun/h within a 70''
circle radius from the central peak. Our reconstructed density profile fits
well an NFW profile with small perturbations due to substructure and is
compatible with the more model dependent analysis of Broadhurst et al. (2004a)
based on the same data. Our estimated mass does not rely on any prior
information about the distribution of dark matter in the cluster. The peak of
the mass distribution falls very close to the central cD and there is
substructure near the center suggesting that the cluster is not fully relaxed.
We also examine the effect on the recovered mass when we include the
uncertainties in the redshift of the sources and in the original shape of the
sources. Using simulations designed to mimic the data, we identify some biases
in our reconstructed mass distribution. We find that the recovered mass is
biased toward lower masses beyond 1 arcmin (150 kpc) from the central cD and
that in the very center we may be affected by degeneracy problems. On the other
hand, we confirm that the reconstructed mass between 25'' and 70'' is a robust,
unbiased estimate of the true mass distribution and is compatible with an NFW
profile.Comment: 11 pages, 12 figures. MNRAS submitted. A full resolution of the paper
can be found in http://darwin.physics.upenn.edu/SLAP
Large-scale structure in a new deep IRAS galaxy redshift survey
We present here the first results from two recently completed, fully sampled redshift surveys comprising 3703 IRAS Faint Source Survey (FSS) galaxies. An unbiased counts-in-cells analysis finds a clustering strength in broad agreement with other recent redshift surveys and at odds with the standard cold dark matter model. We combine our data with those from the QDOT and 1.2 Jy surveys, producing a single estimate of the IRAS galaxy clustering strength. We compare the data with the power spectrum derived from a mixed dark matter universe. Direct comparison of the clustering strength seen in the IRAS samples with that seen in the APM-Stromlo survey suggests b_O/b_I=1.20+/-0.05 assuming a linear, scale independent biasing. We also perform a cell by cell comparison of our FSS-z sample with galaxies from the first CfA slice, testing the viability of a linear-biasing scheme linking the two. We are able to rule out models in which the FSS-z galaxies identically trace the CfA galaxies on scales 5-20h^{-1}Mpc. On scales of 5 and 10h^{-1}Mpc no linear-biasing model can be found relating the two samples. We argue that this result is expected since the CfA sample includes more elliptical galaxies which have different clustering properties from spirals. On scales of 20h^{-1}Mpc no linear-biasing model with b_O/b_I < 1.70 is acceptable. When comparing the FSS-z galaxies to the CfA spirals, however, the two populations trace the same structures within our uncertaintie
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