24,709 research outputs found
The Sloan Great Wall. Morphology and galaxy content
We present the results of the study of the morphology and galaxy content of
the Sloan Great Wall (SGW). We use the luminosity density field to determine
superclusters in the SGW, and the fourth Minkowski functional V_3 and the
morphological signature (the K_1-K_2 shapefinders curve) to show the different
morphologies of the SGW, from a single filament to a multibranching, clumpy
planar system. The richest supercluster in the SGW, SCl~126 and especially its
core resemble a very rich filament, while another rich supercluster in the SGW,
SCl~111, resembles a "multispider" - an assembly of high density regions
connected by chains of galaxies. Using Minkowski functionals we study the
substructure of individual galaxy populations determined by their color in
these superclusters. We assess the statistical significance of the results with
the halo model and smoothed bootstrap. We study the galaxy content and the
properties of groups of galaxies in two richest superclusters of the SGW,
paying special attention to bright red galaxies (BRGs) and to the first ranked
galaxies in SGW groups. About 1/3 of BRGs are spirals. The scatter of colors of
elliptical BRGs is smaller than that of spiral BRGs. About half of BRGs and of
first ranked galaxies in groups have large peculiar velocities. Groups with
elliptical BRGs as their first ranked galaxies populate superclusters more
uniformly than the groups, which have a spiral BRG as its first ranked galaxy.
The galaxy and group content of the core of the supercluster SCl~126 shows
several differences in comparison with the outskirts of this supercluster and
with the supercluster SCl~111. Our results suggest that the formation history
and evolution of individual neighbour superclusters in the SGW has been
different.Comment: Comments: 26 pages, 20 figures, accepted for publication in Ap
CFHTLenS: Weak lensing constraints on the ellipticity of galaxy-scale matter haloes and the galaxy-halo misalignment
We present weak lensing constraints on the ellipticity of galaxy-scale matter
haloes and the galaxy-halo misalignment. Using data from the
Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS), we measure the
weighted-average ratio of the aligned projected ellipticity components of
galaxy matter haloes and their embedded galaxies, , split by
galaxy type. We then compare our observations to measurements taken from the
Millennium Simulation, assuming different models of galaxy-halo misalignment.
Using the Millennium Simulation we verify that the statistical estimator used
removes contamination from cosmic shear. We also detect an additional signal in
the simulation, which we interpret as the impact of intrinsic shape-shear
alignments between the lenses and their large-scale structure environment.
These alignments are likely to have caused some of the previous observational
constraints on to be biased high. From CFHTLenS we find
for early-type galaxies, which is consistent with
current models for the galaxy-halo misalignment predicting . For late-type galaxies we measure
from CFHTLenS. This can be compared to the simulated results which yield
for misaligned late-type models.Comment: 21 pages, 3 tables, 9 figures. This replacement matches the version
accepted for publication in MNRA
Optical Gravitational Lensing Experiment. OGLE-1999-BUL-19: The First Multi-Peak Parallax Event
We describe a highly unusual microlensing event, OGLE-1999-BUL-19, which
exhibits multiple peaks in its light curve. The Einstein radius crossing time
for this event is approximately one year, which is unusually long. We show that
the motion of the Earth induces these multiple peaks in the light curve, since
the relative transverse velocity of the lens projected into the observer plane
is very small (v = 12.5 km/s). This is the lowest velocity so far published and
we believe that this is the first multiple-peak parallax event ever observed.
We also believe that this event may be exhibiting slight binary-source
signatures in addition to these parallax-induced multiple peaks. With
spectroscopic observations it is possible to test this `parallax plus
binary-source' hypothesis and (if this hypothesis turns out to be correct) to
simultaneously fit both models and obtain a measurement of the lens mass.
Furthermore, spectroscopic observations could also supply information regarding
the lens properties, possibly providing another avenue for determining the lens
mass. We found that most of the I-band blending is probably caused by light
from the lens or a binary companion to the source. However, in the V-band,
there appears to be a second blended source 0.35" away from the lensed source.
HST observations will be very useful for understanding the nature of the
blends. We also suggest that a radial velocity survey of all parallax events
will be very useful for further constraining the lensing kinematics and
understanding the origins of these events and the excess of long events toward
the bulge.Comment: 36 pages, 7 figures. Accepted for publication in MNRA
Libration driven elliptical instability
The elliptical instability is a generic instability which takes place in any
rotating flow whose streamlines are elliptically deformed. Up to now, it has
been widely studied in the case of a constant, non-zero differential rotation
between the fluid and the elliptical distortion with applications in
turbulence, aeronautics, planetology and astrophysics. In this letter, we
extend previous analytical studies and report the first numerical and
experimental evidence that elliptical instability can also be driven by
libration, i.e. periodic oscillations of the differential rotation between the
fluid and the elliptical distortion, with a zero mean value. Our results
suggest that intermittent, space-filling turbulence due to this instability can
exist in the liquid cores and sub-surface oceans of so-called synchronized
planets and moons
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