17,185 research outputs found
Star clusters as building blocks for dSph galaxies formation
We study numerically the formation of dSph galaxies. Intense star bursts,
e.g. in gas-rich environments, typically produce a few to a few hundred young
star clusters, within a region of just a few hundred pc. The dynamical
evolution of these star clusters may explain the formation of the luminous
component of dwarf spheroidal galaxies (dSph). Here we perform a numerical
experiment to show that the evolution of star clusters complexes in dark matter
haloes can explain the formation of the luminous components of dSph galaxies.Comment: 4 pages, 4 figures, Proceedings of IAU symposium 266 'Star Clusters -
Basic Building Blocks
The Application of a Cylindrical-spherical Floating Ring Bearing as a Device to Control Stability of Turbogenerators
The development of a new device to control stability of turbogenerators is described. The device comprises a floating ring installed between the journal and bearing housing of a fluid film bearing. The journal and the inner surface of the ring are cylindrical while the outer surface of the ring and bearing surface are spherical providing axial location of the ring and self-alignment of the bearing. The employment of this device would lead to a consistent machine performance. System stability may be controlled by changing a number of bearing and floating ring parameters. This device also offers an additional advantage of having a very low frictional characteristic. A feasibility study was carried out to investigate the suitability of the new device to turbogenerator applications. Both theoretical analysis and experimental observations were carried out. Initial results suggest that the new floating ring device is a competitive alternative to other conventional arrangements
ARCS, The Arcminute Radio Cluster-lens Search - I. Selection Criteria and Initial Results
We present the results of an unbiased radio search for gravitational lensing
events with image separations between 15 and 60 arcsec, which would be
associated with clusters of galaxies with masses >10^{13-14}M_{\sun}. A parent
population of 1023 extended radio sources stronger than 35 mJy with stellar
optical identifications was selected using the FIRST radio catalogue at 1.4 GHz
and the APM optical catalogue. The FIRST catalogue was then searched for
companions to the parent sources stronger than 7 mJy and with separation in the
range 15 to 60 arcsec. Higher resolution observations of the resulting 38 lens
candidates were made with the VLA at 1.4 GHz and 5 GHz, and with MERLIN at 5
GHz in order to test the lens hypothesis in each case. None of our targets was
found to be a gravitational lens system. These results provide the best current
constraint on the lensing rate for this angular scale, but improved
calculations of lensing rates from realistic simulations of the clustering of
matter on the relevant scales are required before cosmologically significant
constraints can be derived from this null result. We now have an efficient,
tested observational strategy with which it will be possible to make an
order-of-magnitude larger unbiased search in the near future.Comment: Accepted for publication in MNRAS. 12 pages, 29 included PostScript
figure
Band Distributions for Quantum Chaos on the Torus
Band distributions (BDs) are introduced describing quantization in a toral
phase space. A BD is the uniform average of an eigenstate phase-space
probability distribution over a band of toral boundary conditions. A general
explicit expression for the Wigner BD is obtained. It is shown that the Wigner
functions for {\em all} of the band eigenstates can be reproduced from the
Wigner BD. Also, BDs are shown to be closer to classical distributions than
eigenstate distributions. Generalized BDs, associated with sets of adjacent
bands, are used to extend in a natural way the Chern-index characterization of
the classical-quantum correspondence on the torus to arbitrary rational values
of the scaled Planck constant.Comment: 12 REVTEX page
A Possible Formation Scenario for Dwarf Spheroidal Galaxies - II: A Parameter Study
Dwarf spheroidal (dSph) galaxies are considered the basic building blocks of
the galaxy formation process in the LCDM (Lambda Cold Dark Matter) hierarchical
cosmological model. These galaxies are believed to be the most dark matter (DM)
dominated systems known, have the lowest stellar content, and are poor in gas.
Many theories attempt to explain the formation of dSph galaxies resorting to
the fact that these galaxies are mainly found orbiting large galaxies or
invoking other mechanisms of interactions. Here we show the full set of
simulation as an extension of our fiducial model, where we study the formation
of classical dSph galaxies in isolation by dissolving star clusters within the
DM halo of the dwarf galaxy. In our parameter survey we adopt cored and cusped
DM halo profiles and consider different numbers of dissolving star clusters. We
investigate the dependency of observable quantities with different masses and
scale-lengths of the DM halo and different star formation efficiencies (SFE).
We find that our proposed scenario explains many features of the classical dSph
galaxies of the Milky Way, like their morphology and their dynamics. We see
trends how the surface brightness and the scale-length of the luminous
component vary with the parameters of our simulations. We also identify how
irregularities in their shape, i.e. clumpiness and ellipticity vary in our
simulations. In velocity space, we identify the parameters leading to flat
velocity dispersions curves. We recognize kinematically cold substructures in
velocity space, named fossil remnants and stemming from our unique initial
conditions, which alter the expected results. These streaming motions are
considered as a key feature for future observation with high resolution to
validate our scenario.Comment: 23 pages, 9 figures, 4 Tables, accepted for publication in MNRA
NICMOS and VLBA observations of the gravitational lens system B1933+503
NICMOS observations of the complex gravitational lens system B1933+503 reveal
infrared counterparts to two of the inverted spectrum radio images. The
infrared images have arc-like structures. The corresponding radio images are
also detected in a VLBA map made at 1.7 GHz with a resolution of 6 mas. We fail
to detect two of the four inverted radio spectrum components with the VLBA even
though they are clearly visible in a MERLIN map at the same frequency at a
different epoch. The absence of these two components could be due to rapid
variability on a time-scale less than the time delay, or to broadening of the
images during propagation of the radio waves through the ISM of the lensing
galaxy to an extent that they fall below the surface brightness detectability
threshold of the VLBA observations. The failure to detect the same two images
with NICMOS is probably due to extinction in the ISM of the lensing galaxy.Comment: 5 pages, 4 figures, submitted to MNRA
Two tails in NGC 3656, and the major merger origin of shell and minor axis dust lane ellipticals
I report on the discovery of two faint (~ 26.8 Rmag/arcsec^2) tidal tails
around the shell elliptical NGC 3656 (Arp 155). This galaxy had previously been
interpreted as a case of accretion, or minor merger. The two tidal tails are
inconsistent with a minor merger, and point instead to a disk-disk major merger
origin. NGC 3656 extends Toomre's merger sequence toward normal elliptical
galaxies, and hints at a major merger origin for shells and minor-axis dust
lanes. A dwarf galaxy lies at the tip of one of the tidal tails. A prominent
shell, which shows sharp azymuthal color discontinuities, belongs to a rotating
dynamical component of young stars which includes the inner dust lane.Comment: 9 pages, 2 plates, 1 figure, uses aaspp.sty, accepted for publication
in The Astrophysical Journal Letters. Files also available by anonymous ftp
at ftp.iac.es, directory ./pub/balcell
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