39,348 research outputs found
Measuring Gravitational Lensing Flexions in Abell 1689 Using an Analytic Image Model
Measuring dark matter substructure within galaxy cluster haloes is a
fundamental probe of the Lambda-CDM model of structure formation. Gravitational
lensing is a technique for measuring the total mass distribution which is
independent of the nature of the gravitating matter, making it a vital tool for
studying these dark-matter dominated objects. We present a new method for
measuring weak gravitational lensing flexions, the gradients of the lensing
shear field, to measure mass distributions on small angular scales. While
previously published methods for measuring flexions focus on measuring derived
properties of the lensed images, such as shapelet coefficients or surface
brightness moments, our method instead fits a
mass-sheet-transformation-invariant Analytic Image Model (AIM) to the each
galaxy image. This simple parametric model traces the distortion of lensed
image isophotes and constrains the flexion fields. We test the AIM method using
simulated data images with realistic noise and a variety of unlensed image
properties, and show that it successfully reproduces the input flexion fields.
We also apply the AIM method for flexion measurement to Hubble Space Telescope
observations of Abell 1689, and detect mass structure in the cluster using
flexions measured with the AIM method.Comment: 44 pages, 4 figures, 3 tables. Accepted to ApJ. V2 (published
version) has minor changes from V1; ApJ 736 (2011
Towards multiple 3D bone surface identification and reconstruction using few 2D X-ray images for intraoperative applications
This article discusses a possible method to use a small number, e.g. 5, of conventional 2D X-ray images to reconstruct multiple 3D bone surfaces intraoperatively. Each bone’s edge contours in X-ray images are automatically identified. Sparse 3D landmark points of each bone are automatically reconstructed by pairing the 2D X-ray images. The reconstructed landmark point distribution on a surface is approximately optimal covering main characteristics of the surface. A statistical shape model, dense point distribution model (DPDM), is then used to fit the reconstructed optimal landmarks vertices to reconstruct a full surface of each bone separately. The reconstructed surfaces can then be visualised and manipulated by surgeons or used by surgical robotic systems
CLASH-VLT: Insights on the mass substructures in the Frontier Fields Cluster MACS J0416.1-2403 through accurate strong lens modeling
We present a detailed mass reconstruction and a novel study on the
substructure properties in the core of the CLASH and Frontier Fields galaxy
cluster MACS J0416.1-2403. We show and employ our extensive spectroscopic data
set taken with the VIMOS instrument as part of our CLASH-VLT program, to
confirm spectroscopically 10 strong lensing systems and to select a sample of
175 plausible cluster members to a limiting stellar mass of log(M_*/M_Sun) ~
8.6. We reproduce the measured positions of 30 multiple images with a
remarkable median offset of only 0.3" by means of a comprehensive strong
lensing model comprised of 2 cluster dark-matter halos, represented by cored
elliptical pseudo-isothermal mass distributions, and the cluster member
components. The latter have total mass-to-light ratios increasing with the
galaxy HST/WFC3 near-IR (F160W) luminosities. The measurement of the total
enclosed mass within the Einstein radius is accurate to ~5%, including
systematic uncertainties. We emphasize that the use of multiple-image systems
with spectroscopic redshifts and knowledge of cluster membership based on
extensive spectroscopic information is key to constructing robust
high-resolution mass maps. We also produce magnification maps over the central
area that is covered with HST observations. We investigate the galaxy
contribution, both in terms of total and stellar mass, to the total mass budget
of the cluster. When compared with the outcomes of cosmological -body
simulations, our results point to a lack of massive subhalos in the inner
regions of simulated clusters with total masses similar to that of MACS
J0416.1-2403. Our findings of the location and shape of the cluster dark-matter
halo density profiles and on the cluster substructures provide intriguing tests
of the assumed collisionless, cold nature of dark matter and of the role played
by baryons in the process of structure formation.Comment: 26 pages, 22 figures, 7 tables; accepted for publication in the
Astrophysical Journal. A high-resolution version is available at
https://sites.google.com/site/vltclashpublic/publications/Grillo_etal_2014.pd
Kinect Range Sensing: Structured-Light versus Time-of-Flight Kinect
Recently, the new Kinect One has been issued by Microsoft, providing the next
generation of real-time range sensing devices based on the Time-of-Flight (ToF)
principle. As the first Kinect version was using a structured light approach,
one would expect various differences in the characteristics of the range data
delivered by both devices. This paper presents a detailed and in-depth
comparison between both devices. In order to conduct the comparison, we propose
a framework of seven different experimental setups, which is a generic basis
for evaluating range cameras such as Kinect. The experiments have been designed
with the goal to capture individual effects of the Kinect devices as isolatedly
as possible and in a way, that they can also be adopted, in order to apply them
to any other range sensing device. The overall goal of this paper is to provide
a solid insight into the pros and cons of either device. Thus, scientists that
are interested in using Kinect range sensing cameras in their specific
application scenario can directly assess the expected, specific benefits and
potential problem of either device.Comment: 58 pages, 23 figures. Accepted for publication in Computer Vision and
Image Understanding (CVIU
Why Chromatic Imaging Matters
During the last two decades, the first generation of beam combiners at the
Very Large Telescope Interferometer has proved the importance of optical
interferometry for high-angular resolution astrophysical studies in the near-
and mid-infrared. With the advent of 4-beam combiners at the VLTI, the u-v
coverage per pointing increases significantly, providing an opportunity to use
reconstructed images as powerful scientific tools. Therefore, interferometric
imaging is already a key feature of the new generation of VLTI instruments, as
well as for other interferometric facilities like CHARA and JWST. It is thus
imperative to account for the current image reconstruction capabilities and
their expected evolutions in the coming years. Here, we present a general
overview of the current situation of optical interferometric image
reconstruction with a focus on new wavelength-dependent information,
highlighting its main advantages and limitations. As an Appendix we include
several cookbooks describing the usage and installation of several state-of-the
art image reconstruction packages. To illustrate the current capabilities of
the software available to the community, we recovered chromatic images, from
simulated MATISSE data, using the MCMC software SQUEEZE. With these images, we
aim at showing the importance of selecting good regularization functions and
their impact on the reconstruction.Comment: Accepted for publication in Experimental Astronomy as part of the
topical collection: Future of Optical-infrared Interferometry in Europ
3D Object Reconstruction from Imperfect Depth Data Using Extended YOLOv3 Network
State-of-the-art intelligent versatile applications provoke the usage of full 3D, depth-based streams, especially in the scenarios of intelligent remote control and communications, where virtual and augmented reality will soon become outdated and are forecasted to be replaced by point cloud streams providing explorable 3D environments of communication and industrial data. One of the most novel approaches employed in modern object reconstruction methods is to use a priori knowledge of the objects that are being reconstructed. Our approach is different as we strive to reconstruct a 3D object within much more difficult scenarios of limited data availability. Data stream is often limited by insufficient depth camera coverage and, as a result, the objects are occluded and data is lost. Our proposed hybrid artificial neural network modifications have improved the reconstruction results by 8.53 which allows us for much more precise filling of occluded object sides and reduction of noise during the process. Furthermore, the addition of object segmentation masks and the individual object instance classification is a leap forward towards a general-purpose scene reconstruction as opposed to a single object reconstruction task due to the ability to mask out overlapping object instances and using only masked object area in the reconstruction process
Testing the Evolution of the Correlations between Supermassive Black Holes and their Host Galaxies using Eight Strongly Lensed Quasars
One of the main challenges in using high redshift active galactic nuclei to
study the correlations between the mass of the supermassive Black Hole (MBH)
and the properties of their active host galaxies is instrumental resolution.
Strong lensing magnification effectively increases instrumental resolution and
thus helps to address this challenge. In this work, we study eight strongly
lensed active galactic nuclei (AGN) with deep Hubble Space Telescope imaging,
using the lens modelling code Lenstronomy to reconstruct the image of the
source. Using the reconstructed brightness of the host galaxy, we infer the
host galaxy stellar mass based on stellar population models. MBH are estimated
from broad emission lines using standard methods. Our results are in good
agreement with recent work based on non-lensed AGN, demonstrating the potential
of using strongly lensed AGNs to extend the study of the correlations to higher
redshifts. At the moment, the sample size of lensed AGN is small and thus they
provide mostly a consistency check on systematic errors related to resolution
for the non-lensed AGN. However, the number of known lensed AGN is expected to
increase dramatically in the next few years, through dedicated searches in
ground and space based wide field surveys, and they may become a key diagnostic
of black hole and galaxy co-evolution.Comment: 12 pages, 4 figures, 3 tables. MNRAS in press. Comments welcom
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