19,686 research outputs found
The Arrowhead Mini-Supercluster of Galaxies
Superclusters of galaxies can be defined kinematically from local evaluations
of the velocity shear tensor. The location where the smallest eigenvalue of the
shear is positive and maximal defines the center of a basin of attraction.
Velocity and density fields are reconstructed with Wiener Filter techniques.
Local velocities due to the density field in a restricted region can be
separated from external tidal flows, permitting the identification of
boundaries separating inward flows toward a basin of attraction and outward
flows. This methodology was used to define the Laniakea Supercluster that
includes the Milky Way. Large adjacent structures include Perseus-Pisces, Coma,
Hercules, and Shapley but current kinematic data are insufficient to capture
their full domains. However there is a small region trapped between Laniakea,
Perseus-Pisces, and Coma that is close enough to be reliably characterized and
that satisfies the kinematic definition of a supercluster. Because of its
shape, it is given the name the Arrowhead Supercluster. This entity does not
contain any major clusters. A characteristic dimension is ~25 Mpc and the
contained mass is only ~10^15 Msun.Comment: Accepted for publication in The Astrophysical Journal. Video can be
viewed at http://irfu.cea.fr/arrowhea
3D Shape Reconstruction from Sketches via Multi-view Convolutional Networks
We propose a method for reconstructing 3D shapes from 2D sketches in the form
of line drawings. Our method takes as input a single sketch, or multiple
sketches, and outputs a dense point cloud representing a 3D reconstruction of
the input sketch(es). The point cloud is then converted into a polygon mesh. At
the heart of our method lies a deep, encoder-decoder network. The encoder
converts the sketch into a compact representation encoding shape information.
The decoder converts this representation into depth and normal maps capturing
the underlying surface from several output viewpoints. The multi-view maps are
then consolidated into a 3D point cloud by solving an optimization problem that
fuses depth and normals across all viewpoints. Based on our experiments,
compared to other methods, such as volumetric networks, our architecture offers
several advantages, including more faithful reconstruction, higher output
surface resolution, better preservation of topology and shape structure.Comment: 3DV 2017 (oral
Reconstructing Probability Distributions with Gaussian Processes
Modern cosmological analyses constrain physical parameters using Markov Chain
Monte Carlo (MCMC) or similar sampling techniques. Oftentimes, these techniques
are computationally expensive to run and require up to thousands of CPU hours
to complete. Here we present a method for reconstructing the log-probability
distributions of completed experiments from an existing MCMC chain (or any set
of posterior samples). The reconstruction is performed using Gaussian process
regression for interpolating the log-probability. This allows for easy
resampling, importance sampling, marginalization, testing different samplers,
investigating chain convergence, and other operations. As an example use-case,
we reconstruct the posterior distribution of the most recent Planck 2018
analysis. We then resample the posterior, and generate a new MCMC chain with
forty times as many points in only thirty minutes. Our likelihood
reconstruction tool can be found online at
https://github.com/tmcclintock/AReconstructionTool.Comment: 7 pages, 4 figures, repository at
https://github.com/tmcclintock/AReconstructionToo
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
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