1,827 research outputs found
Approximate analysis of thermal convection in a crystal-growth cell for Spacelab 3
The transient and steady thermal convection in microgravity is described. The approach is applicable to many three dimensional flows in containers of various shapes with various thermal gradients imposed. The method employs known analytical solutions to two dimensional thermal flows in simpler geometries, and does not require recourse to numerical calculations by computer
The Fundamental Plane of Radio Galaxies
We collected photometrical and dynamical data for 73 low red-shift (z<0.2)
Radio Galaxies (LzRG) in order to study their Fundamental Plane (FP). For 22
sources we also present new velocity dispersion data, that complement the
photometric data given in our previous study of LzRG (Govoni et al. 2000a). It
is found that the FP of LzRG is similar to the one defined by non-active
elliptical galaxies, with LzRG representing the brightest end of the population
of early type galaxies. Since the FP mainly reflects the virial equilibrium
condition, our result implies that the global properties of early--type
galaxies (defining the FP) are not influenced by the presence of gas accretion
in the central black hole. This is fully in agreement with the recent results
in black hole demography, showing that virtually all luminous spheroidal
galaxies host a massive black hole and therefore may potentially become active.
We confirm and extend to giant ellipticals the systematic increase of the
mass-to-light ratio with galaxy luminosity.Comment: 8 pages, 3 figures, accepted for publication in A&
Two scenarios for avalanche dynamics in inclined granular layers
We report experimental measurements of avalanche behavior of thin granular
layers on an inclined plane for low volume flow rate. The dynamical properties
of avalanches were quantitatively and qualitatively different for smooth glass
beads compared to irregular granular materials such as sand. Two scenarios for
granular avalanches on an incline are identified and a theoretical explanation
for these different scenarios is developed based on a depth-averaged approach
that takes into account the differing rheologies of the granular materials.Comment: 4 pages, 4 figures, accepted to Phys. Rev. Let
Galaxy Harassment and the Evolution of Clusters of Galaxies
Disturbed spiral galaxies with high rates of star formation pervaded clusters
of galaxies just a few billion years ago, but nearby clusters exclude spirals
in favor of ellipticals. ``Galaxy harassment" (frequent high speed galaxy
encounters) drives the morphological transformation of galaxies in clusters,
provides fuel for quasars in subluminous hosts and leaves detectable debris
arcs. Simulated images of harassed galaxies are strikingly similar to the
distorted spirals in clusters at observed by the Hubble Space
Telescope.Comment: Submitted to Nature. Latex file, 7 pages, 10 photographs in gif and
jpeg format included. 10 compressed postscript figures and text available
using anonymous ftp from ftp://ftp-hpcc.astro.washington.edu/pub/hpcc/moore/
(mget *) Also available at http://www-hpcc.astro.washington.edu/papers
Fast and slow rotators in the densest environments: a FLAMES/GIRAFFE IFS study of galaxies in Abell 1689 at z=0.183
We present FLAMES/GIRAFFE integral field spectroscopy of 30 galaxies in the
massive cluster Abell 1689 at z = 0.183. Conducting an analysis similar to that
of ATLAS3D, we extend the baseline of the kinematic morphology-density relation
by an order of magnitude in projected density and show that it is possible to
use existing instruments to identify slow and fast rotators beyond the local
Universe. We find 4.5 +- 1.0 slow rotators with a distribution in magnitude
similar to those in the Virgo cluster. The overall slow rotator fraction of our
Abell 1689 sample is 0.15 +- 0.03, the same as in Virgo using our selection
criteria. This suggests that the fraction of slow rotators in a cluster is not
strongly dependent on its density. However, within Abell 1689, we find that the
fraction of slow rotators increases towards the centre, as was also found in
the Virgo cluster.Comment: Accepted by MNRA
Dynamics of precipitation pattern formation at geothermal hot springs
We formulate and model the dynamics of spatial patterns arising during the
precipitation of calcium carbonate from a supersaturated shallow water flow.
The model describes the formation of travertine deposits at geothermal hot
springs and rimstone dams of calcite in caves. We find explicit solutions for
travertine domes at low flow rates, identify the linear instabilities which
generate dam and pond formation on sloped substrates, and present simulations
of statistical landscape evolution
Numerical simulation of small perturbation on an accretion disk due to the collision of a star with the disk near the black hole
In this paper, perturbations of an accretion disk by a star orbiting around a
black hole are studied. We report on a numerical experiment, which has been
carried out by using a parallel-machine code originally developed by D\"{o}nmez
(2004). An initially steady state accretion disk near a non-rotating
(Schwarzschild) black hole interacts with a "star", modeled as an initially
circular region of increased density. Part of the disk is affected by the
interaction. In some cases, a gap develops and shock wave propagates through
the disk. We follow the evolution for order of one dynamical period and we show
how the non-axisymetric density perturbation further evolves and moves
downwards where the material of the disk and the star become eventually
accreted onto the central body.
When the star perturbs the steady state accretion disk, the disk around the
black hole is destroyed by the effect of perturbation. The perturbed accretion
disk creates a shock wave during the evolution and it loses angular momentum
when the gas hits on the shock waves. Colliding gas with the shock wave is the
one of the basic mechanism of emitting the rays in the accretion disk. The
series of supernovae occurring in the inner disk could entirely destroy the
disk in that region which leaves a more massive black hole behind, at the
center of galaxies.Comment: 20pages, 8 figures, accepted for publication in Astrophysics and
Space Scienc
HCG 16 Revisited: Clues About Galaxy Evolution in Groups
We present new spectroscopic observations of 5 galaxies, members of the
unusually active compact group HCG 16, observed using the Palomar 5m telescope.
The high signal to noise ratios (S/N ) of the spectra allow us to
study the variation of the emission line characteristics and the stellar
populations in the nucleus and the circumnuclear regions of the galaxies. The
emission line characteristics of these galaxies are complex, varying between
Seyfert 2 and LINERs or between LINERs and starbursts. All of the galaxies show
traces of intermediate age stellar populations, supporting our previous result
that post-starburst galaxies are common in compact groups. The galaxies
HCG16--4 and HCG16--5 show double nuclei and therefore could be two cases of
recent merger. Our observations support a scenario where HCG 16 was formed by
the successive merger of metal poor, low mass galaxies. The galaxies HCG16--1
and HCG16--2, which are more evolved, form the old core of the group. Galaxies
HCG16--4 and HCG16--5 are two more recent additions still in a merging phase.
Galaxy HCG16--5 is a starburst galaxy which is just beginning to fall into the
core. If HCG 16 is representative of compact groups in their early stage, the
whole set of observations implies that the formation of compact groups is the
result of hierarchical galaxy formation. HCG 16 could be one example of this
process operating in the local universe.Comment: tar file containing text and figures is available at
http://www.daf.on.br/~reinaldo/paper.htm
UV Imaging of the Galaxy Cluster CL0939+4713 (Abell 851) at z=0.41
The first UV F300W and F218W WFPC2 observations of the rich galaxy cluster
CL0939+4713 at z=0.41 are presented and discussed. UV/optical two-color and c-m
diagrams of the sources detected in the F300W waveband are constructed. Thanks
to pre-existing HST optical images of the same field a morphological
classification for the majority of these objects is also provided. Moreover,
taking advantage of recent redshift surveys along CL0939+4713 line of sight,
separate diagrams comparing the properties of galaxies belonging to the cluster
and to its close projected field are presented. Possible evolutionary effects
in the UV from z~0.4 to present time are investigated by comparing the
restframe [mid-UV-Optical] colors of galaxies in CL0939+4713 with balloon-borne
data of the Coma cluster, as well as by resorting to suitable galaxy evolution
models. Finally, current attempts to constrain the epoch of the UV-upturn onset
in evolved populations by means of HST UV observations are discussed.Comment: 20 pages, LaTeX, with 6 PostScript figures, Submitted to The
Astrophysical Journal, Figures 1 and 2 have lower resolution than the ApJ
submitted versio
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