47 research outputs found
A Multi-Resolution Weak Lensing Mass Reconstruction Method
Motivated by the limitations encountered with the commonly used direct
reconstruction techniques of producing mass maps, we have developed a
multi-resolution maximum-likelihood reconstruction method for producing two
dimensional mass maps using weak gravitational lensing data. To utilize all the
shear information, we employ an iterative inverse method with a properly
selected regularization coefficient which fits the deflection potential at the
position of each galaxy. By producing mass maps with multiple resolutions in
the different parts of the observed field, we can achieve a comparable level of
signal to noise by increasing the resolution in regions of higher distortions
or regions with an over-density of background galaxies. In addition, we are
able to better study the sub-structure of the massive clusters at a resolution
which is not attainable in the rest of the observed field. We apply our method
to the simulated data and to a four square degree field obtained by the Deep
Lens Survey.Comment: Preprint (30 pages, 10 figures), Submitted to Ap
Discovery of a Galaxy Cluster via Weak Lensing
We report the discovery of a cluster of galaxies via its weak gravitational
lensing effect on background galaxies, the first spectroscopically confirmed
cluster to be discovered through its gravitational effects rather than by its
electromagnetic radiation. This fundamentally different selection mechanism
promises to yield mass-selected, rather than baryon or photon-selected, samples
of these important cosmological probes. We have confirmed this cluster with
spectroscopic redshifts of fifteen members at z=0.276, with a velocity
dispersion of 615 km/s. We use the tangential shear as a function of source
photometric redshift to estimate the lens redshift independently and find z_l =
0.30 +- 0.08. The good agreement with the spectroscopy indicates that the
redshift evolution of the mass function may be measurable from the imaging data
alone in shear-selected surveys.Comment: revised version with minor changes, to appear in ApJ
The Landau gauge gluon and ghost propagator in the refined Gribov-Zwanziger framework in 3 dimensions
In previous works, we have constructed a refined version of the
Gribov-Zwanziger action in 4 dimensions, by taking into account a novel
dynamical effect. In this paper, we explore the 3-dimensional case. Analogously
as in 4 dimensions, we obtain a ghost propagator behaving like in the
infrared, while the gluon propagator reaches a finite nonvanishing value at
zero momentum. Simultaneously, a clear violation of positivity by the gluon
propagator is also found. This behaviour of the propagators turns out be in
agreement with the recent numerical simulations.Comment: 26 pages, 16 .eps figures. v3: version accepted for publication in
Phys Rev
A refinement of the Gribov-Zwanziger approach in the Landau gauge: infrared propagators in harmony with the lattice results
Recent lattice data have reported an infrared suppressed, positivity
violating gluon propagator which is nonvanishing at zero momentum and a ghost
propagator which is no longer enhanced. This paper discusses how to obtain
analytical results which are in qualitative agreement with these lattice data
within the Gribov-Zwanziger framework. This framework allows one to take into
account effects related to the existence of gauge copies, by restricting the
domain of integration in the path integral to the Gribov region. We elaborate
to great extent on a previous short paper by presenting additional results,
also confirmed by the numerical simulations. A detailed discussion on the soft
breaking of the BRST symmetry arising in the Gribov-Zwanziger approach is
provided.Comment: 38 pages, 9 figures, the content of section V has been extended and
adapte
An ASCA Study of the Heavy Element Distribution in Clusters of Galaxies
We perform a spatially resolved X-ray spectroscopic study of a set of 11
relaxed clusters of galaxies observed by the ROSAT/PSPC and ASCA/SIS. Using a
method which corrects for the energy dependent effects of the ASCA PSF based on
ROSAT images, we constrain the spatial distribution of Ne, Si, S and Fe in each
cluster. Theoretical prescriptions for the chemical yields of Type Ia and II
supernovae, then allow determination of the Fe enrichment from both types of
supernovae as a function of radius within each cluster. Using optical
measurements from the literature, we also determine the iron mass-to-light
ratio (IMLR) separately for Fe synthesized in both types of supernovae. For
clusters with the best photon statistics, we find that the total Fe abundance
decreases significantly with radius, while the Si abundance is either flat or
decreases less rapidly, resulting in an increasing Si/Fe ratio with radius.
This result indicates a greater predominance of Type II SNe enrichment at large
radii in clusters. We suggest that the high Si/Fe ratios in the outskirts of
rich clusters may arise from enrichment by Type II SNe released to ICM via
galactic star burst driven winds. Abridged.Comment: 17 pages, ApJ in press (Nov. 2000), a study of systematics is adde
Weak Lensing Discovery and Tomography of a Cluster at z=0.68
We report the weak lensing discovery, spectroscopic confirmation, and weak
lensing tomography of a massive cluster of galaxies at , demonstrating
that shear selection of clusters works at redshifts high enough to be
cosmologically interesting. The mass estimate from weak lensing, solar masses within projected radius r, agrees with that
derived from the spectroscopy (), and with the
position of an arc which is likely to be a strongly lensed background galaxy.
The redshift estimate from weak lensing tomography is consistent with the
spectroscopy, demonstrating the feasibility of baryon-unbiased mass surveys.
This tomographic technique will be able to roughly identify the redshifts of
any dark clusters which may appear in shear-selected samples, up to z ~ 1.Comment: Final version. Substantially expanded from first version, including
more detail, more figures, and more mass estimates, including an M/L
estimate. Basic conclusions unchange
Smooth Bosonization as a Quantum Canonical Transformation
We consider a 1+1 dimensional field theory which contains both a complex
fermion field and a real scalar field. We then construct a unitary operator
that, by a similarity transformation, gives a continuum of equivalent theories
which smoothly interpolate between the massive Thirring model and the
sine-Gordon model. This provides an implementation of smooth bosonization
proposed by Damgaard et al. as well as an example of a quantum canonical
transformation for a quantum field theory.Comment: 20 pages, revte
Kinematics and Mass Profile of AWM 7
We have measured 492 redshifts (311 new) in the direction of the poor cluster
AWM~7 and have identified 179 cluster members (73 new). We use two independent
methods to derive a self-consistent mass profile, under the assumptions that
the absorption-line galaxies are virialized and that they trace an underlying
Navarro, Frenk & White (1997) dark matter profile: (1) we fit such an NFW
profile to the radial distribution of galaxy positions and to the velocity
dispersion profile; (2) we apply the virial mass estimator to the cluster. With
these assumptions, the two independent mass estimates agree to \sim 15% within
1.7 h^{-1} Mpc, the radial extent of our data; we find an enclosed mass \sim
(3+-0.5)\times 10^{14} h^{-1} M_\odot. The largest potential source of
systematic error is the inclusion of young emission-line galaxies in the mass
estimate.
We investigate the behavior of the surface term correction to the virial mass
estimator under several assumptions about the velocity anisotropy profile,
still within the context of the NFW model, and remark on the sensitivity of
derived mass profiles to outliers. We find that one must have data out to a
large radius in order to determine the mass robustly, and that the surface term
correction is unreliable at small radii.Comment: LaTeX, 5 tables, 7 figures, appeared as 2000 AJ 119 44; typos and Eq.
9 corrected; results are unaffecte
On fermionic tilde conjugation rules and thermal bosonization. Hot and cold thermofields
A generalization of Ojima tilde conjugation rules is suggested, which reveals
the coherent state properties of thermal vacuum state and is useful for the
thermofield bosonization. The notion of hot and cold thermofields is introduced
to distinguish different thermofield representations giving the correct normal
form of thermofield solution for finite temperature Thirring model with correct
renormalization and anticommutation properties.Comment: 13 page
Caltech Faint Galaxy Redshift Survey X: A Redshift Survey in the Region of the Hubble Deep Field North
A redshift survey has been carried out in the region of the Hubble Deep Field
North using the Low Resolution Imaging Spectrograph at the Keck Observatory.
The resulting redshift catalog, which contains 671 entries, is a compendium of
our own data together with published LRIS/Keck data. It is more than 92%
complete for objects, irrespective of morphology, to mag in the HDF
itself and to mag in the Flanking Fields within a diameter of 8 arcmin
centered on the HDF, an unusually high completion for a magnitude limited
survey performed with a large telescope. A median redshift is reached
at .
Strong peaks in the redshift distribution, which arise when a group or poor
cluster of galaxies intersect the area surveyed, can be identified to in this dataset. More than 68% of the galaxies are members of these
redshift peaks. In a few cases, closely spaced peaks in can be resolved
into separate groups of galaxies that can be distinguished in both velocity and
location on the sky.
The radial separation of these peaks in the pencil-beam survey is consistent
with a characteristic length scale for the their separation of 70 Mpc
in our adopted cosmology (, ). Strong
galaxy clustering is in evidence at all epochs back to . (abstract
abridged)Comment: Accepted to the ApJ. This version contains all the figures and
tables. 2 minor typos in table 2b correcte