1,372 research outputs found
Visual Search for Galaxies near the Northern Crossing of the Supergalactic plane by the Milky Way
We have visually examined twelve Palomar red Plates for galaxies at low
Galactic latitude b, where the Supergalactic Plane (SGP) is crossed by the
Galactic Plane (GP), at Galactic longitude l ~135 degrees. The catalogue
consists of 2575 galaxy candidates, of which 462 have major axis diameters d >=
0.8 arc min (uncorrected for extinction). Galaxy candidates can be identified
down to |b| ~ 0 degrees. One of our galaxy candidates (J24 = Dwingeloo 1) has
recently been discovered independently in 21cm by Kraan-Korteweg et al. (1994)
as a nearby galaxy. Comparisons with the structures seen in the IRAS and UGC
catalogues are made. We compare the success rate of identifying galaxies using
the IRAS Point Source Catalogue under different colour selection criteria. The
criteria that require both the 60 micron and 100 micron fluxes to be of high
quality, have the highest probability of selecting a galaxy (with d >= 0.6 arc
min), but at the expense of selecting a smaller number of galaxies in total.Comment: uuencoded compressed postscript, without figures. The figures are
available at http://www.ast.cam.ac.uk/preprint/PrePrint.htm
The puzzlingly large Ca II triplet absorption in dwarf elliptical galaxies
We present central CaT, PaT, and CaT* indices for a sample of fifteen dwarf
elliptical galaxies (dEs). Twelve of these have CaT* ~ 7 A and extend the
negative correlation between the CaT* index and central velocity dispersion
sigma, which was derived for bright ellipticals (Es), down to 20 < sigma < 55
km/s. For five dEs we have independent age and metallicity estimates. Four of
these have CaT* ~ 7 A, much higher than expected from their low metallicities
(-1.5 < [Z/H] < -0.5). The observed anti-correlation of CaT* as a function of
sigma or Z is in flagrant disagreement with theory. We discuss some of the
amendments that have been proposed to bring the theoretical predictions into
agreement with the observed CaT*-values of bright Es and how they can be
extended to incorporate also the observed CaT*-values of dEs. Moreover, 3 dEs
in our sample have CaT* ~ 5 A, as would be expected for metal-poor stellar
systems. Any theory for dE evolution will have to be able to explain the
co-existence of low-CaT* and high-CaT* dEs at a given mean metallicity. This
could be the first direct evidence that the dE population is not homogeneous,
and that different evolutionary paths led to morphologically and kinematically
similar but chemically distinct objects.Comment: 4 pages, 3 figures, accepted for publication in ApJ Letter
Limitations of light delay and storage times in EIT experiments with condensates
We investigate the limitations arising from atomic collisions on the storage
and delay times of probe pulses in EIT experiments. We find that the atomic
collisions can be described by an effective decay rate that limits storage and
delay times. We calculate the momentum and temperature dependence of the decay
rate and find that it is necessary to excite atoms at a particular momentum
depending on temperature and spacing of the energy levels involved in order to
minimize the decoherence effects of atomic collisions.Comment: 4 pages RevTeX, 4 figures. Send correspondence to
[email protected]
Fish schooling as a basis for vertical axis wind turbine farm design
Most wind farms consist of horizontal axis wind turbines (HAWTs) due to the
high power coefficient (mechanical power output divided by the power of the
free-stream air through the turbine cross-sectional area) of an isolated
turbine. However when in close proximity to neighbouring turbines, HAWTs suffer
from a reduced power coefficient. In contrast, previous research on vertical
axis wind turbines (VAWTs) suggests that closely-spaced VAWTs may experience
only small decreases (or even increases) in an individual turbine's power
coefficient when placed in close proximity to neighbours, thus yielding much
higher power outputs for a given area of land. A potential flow model of
inter-VAWT interactions is developed to investigate the effect of changes in
VAWT spatial arrangement on the array performance coefficient, which compares
the expected average power coefficient of turbines in an array to a
spatially-isolated turbine. A geometric arrangement based on the configuration
of shed vortices in the wake of schooling fish is shown to significantly
increase the array performance coefficient based upon an array of 16x16 wind
turbines. Results suggest increases in power output of over one order of
magnitude for a given area of land as compared to HAWTs.Comment: Submitted for publication in BioInspiration and Biomimetics. Note:
The technology described in this paper is protected under both US and
international pending patents filed by the California Institute of Technolog
GASP II. A MUSE view of extreme ram-pressure stripping along the line of sight: kinematics of the jellyfish galaxy JO201
This paper presents a spatially-resolved kinematic study of the jellyfish
galaxy JO201, one of the most spectacular cases of ram-pressure stripping (RPS)
in the GASP (GAs Stripping Phenomena in Galaxies with MUSE) survey. By studying
the environment of JO201, we find that it is moving through the dense
intra-cluster medium of Abell 85 at supersonic speeds along our line of sight,
and that it is likely accompanied by a small group of galaxies. Given the
density of the intra-cluster medium and the galaxy's mass, projected position
and velocity within the cluster, we estimate that JO201 must so far have lost
~50% of its gas during infall via RPS. The MUSE data indeed reveal a smooth
stellar disk, accompanied by large projected tails of ionised (Halpha) gas,
composed of kinematically cold (velocity dispersion <40km/s) star-forming knots
and very warm (>100km/s) diffuse emission which extend out to at least ~50 kpc
from the galaxy centre. The ionised Halpha-emitting gas in the disk rotates
with the stars out to ~6 kpc but in the disk outskirts becomes increasingly
redshifted with respect to the (undisturbed) stellar disk. The observed
disturbances are consistent with the presence of gas trailing behind the
stellar component, resulting from intense face-on RPS happening along the line
of sight. Our kinematic analysis is consistent with the estimated fraction of
lost gas, and reveals that stripping of the disk happens outside-in, causing
shock heating and gas compression in the stripped tails.Comment: ApJ, revised version after referee comments, 15 pages, 16 figures.
The interactive version of Figure 9 can be viewed at
web.oapd.inaf.it/gasp/publications.htm
Imaging of the Shell Galaxies NGC 474 and NGC 7600, and Implications for their Formation
We present photometric observations of two shell galaxies, NGC 474 and NGC
7600. We examine the photometric colours and surface brightnesses of the shells
and their host galaxies, and the isophotal parameters of each galaxy. In the
case of NGC 474, we find that the shell formation is consistent with a merger
origin although it is possible that the close companion NGC 470 is contributing
to the shell system via mass transfer. NGC 7600 exhibits shell geometry and
colours which also favour a merger origin.Comment: Accepted by MNRA
The shell elliptical NGC2865: evolutionary population synthesis of a kinematically distinct core
We report on the discovery of a rapidly co-rotating stellar and gas component
in the nucleus of the shell elliptical NGC2865. The stellar component extends ~
0.51/h100 kpc along the major axis, and shows depressed velocity dispersion and
absorption line profiles skewed in the opposite sense to the mean velocity.
Associated with it is a young stellar population with enhanced \hbeta, lowered
Mg and same Fe indices relative to the underlying elliptical. Its recent star
formation history is constrained by considering ``bulge+burst'' models under 4
physically motivated scenarios, using evolutionary population synthesis.
Scenarios in which the nuclear component is formed over a Hubble time or
recently from continuous gas inflow are ruled out.
Our results argue for a gas-rich accretion or merger origin for the shells
and kinematic subcomponent in NGC2865. Arguments based on stellar populations
and gas dynamics suggest that one of the progenitors is likely a Sb or Sc
spiral. We demonstrate that despite the age and metallicity degeneracy of the
underlying elliptical, the age and metallicity of the kinematic subcomponent
can be constrained. This work strengthens the link between KDCs and shells, and
demonstrates that a KDC can be formed from a late merger.Comment: 26 pages, accepted for publication in MNRA
Exact Cover with light
We suggest a new optical solution for solving the YES/NO version of the Exact
Cover problem by using the massive parallelism of light. The idea is to build
an optical device which can generate all possible solutions of the problem and
then to pick the correct one. In our case the device has a graph-like
representation and the light is traversing it by following the routes given by
the connections between nodes. The nodes are connected by arcs in a special way
which lets us to generate all possible covers (exact or not) of the given set.
For selecting the correct solution we assign to each item, from the set to be
covered, a special integer number. These numbers will actually represent delays
induced to light when it passes through arcs. The solution is represented as a
subray arriving at a certain moment in the destination node. This will tell us
if an exact cover does exist or not.Comment: 20 pages, 4 figures, New Generation Computing, accepted, 200
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Reconnection in NIMROD: Model, Predictions, Remedies
It is shown that in NIMROD the formation of closed current configurations, occurring only after the voltage is turned off, is due to the faster resistive decay of nonsymmetric modes compared to the symmetric projection of the 3D steady state achieved by gun injection. Implementing Spitzer resistivity is required to make a definitive comparison with experiment, using two experimental signatures of the model discussed in the paper. If there are serious disagreements, it is suggested that a phenomenological hyper-resistivity be added to the n = 0 component of Ohm's law, similar to hyper-resistive Corsica models that appear to fit experiments. Hyper-resistivity might capture physics at small scale missed by NIMROD. Encouraging results would motivate coupling NIMROD to SPICE with edge physics inspired by UEDGE, as a tool for experimental data analysis
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