36,039 research outputs found
An IRAS High Resolution Image Restoration (HIRES) Atlas of All Interacting Galaxies in the IRAS Revised Bright Galaxy Sample
We present high-resolution (30"-1') 12, 25, 60, and 100 micron images of 106
interacting galaxy systems contained in the IRAS Revised Bright Galaxy Sample
(RBGS, Sanders et al. 2003), a complete sample of all galaxies having a 60
micron flux density greater than 5.24 Jy. These systems were selected to have
at least two distinguishable galaxies separated by less than three average
galactic diameters, and thus we have excluded very widely separated systems and
very advanced mergers. The new complete survey has the same properties as the
prototype survey of Surace et al. 1993. We find no increased tendency for
infrared-bright galaxies to be associated with other infrared bright galaxies
among the widely separated pairs studied here. We find small enhancements in
far-infrared activity in multiple galaxy systems relative to RBGS
non-interacting galaxies with the same blue luminosity distribution. We also
find no differences in infrared activity (as measured by infrared color and
luminosity) between late and early-type spiral galaxies.Comment: 49 pages, 13 figures. To appear in the Astronomical Journal. Figures
have been degraded due to space considerations. A PDF version with higher
quality figures is available at
http://humu.ipac.caltech.edu/~jason/pubs/surace_hires.pd
Two-Color Terawatt Laser System For High-Intensity Laser-Plasma Experiments
We report a two-color terawatt laser system for use in controlling laser-plasma instabilities. The system includes a commercial 45 TW Ti:Sapphire laser system at 800 nm, temporally synchronized with a 1 TW CPA Raman-Ti:Sapphire hybrid laser centered at 873nm that we designed and built to complement the 800 nm system. The two-color system will be used to seed, enhance, suppress, or otherwise control a variety of instabilities which arise in laser-plasma interactions.Physic
X-ray emission from the Ultramassive Black Hole candidate NGC1277: implications and speculation on its origin
We study the X-ray emission from NGC1277, a galaxy in the core of the Perseus
cluster, for which van den Bosch et al. have recently claimed the presence of
an UltraMassive Black Hole (UMBH) of mass 1.7 times 10^10 Msun, unless the IMF
of the stars in the stellar bulge is extremely bottom heavy. The X-rays
originate in a power-law component of luminosity 1.3 times 10^40 erg/s embedded
in a 1 keV thermal minicorona which has a half-light radius of about 360 pc,
typical of many early-type galaxies in rich clusters of galaxies. If Bondi
accretion operated onto the UMBH from the minicorona with a radiative
efficiency of 10 per cent, then the object would appear as a quasar with
luminosity 10^46 erg/s, a factor of almost 10^6 times higher than observed. The
accretion flow must be highly radiatively inefficient, similar to past results
on M87 and NGC3115. The UMBH in NGC1277 is definitely not undergoing any
significant growth at the present epoch. We note that there are 3 UMBH
candidates in the Perseus cluster and that the inferred present mean mass
density in UMBH could be 10^5 Msun/Mpc^3, which is 20 to 30 per cent of the
estimated mean mass density of all black holes. We speculate on the implied
growth of UMBH and their hosts, and discuss the possibiity that extreme AGN
feedback could make all UMBH host galaxies have low stellar masses at redshifts
around 3. Only those which end up at the centres of groups and clusters later
accrete large stellar envelopes and become Brightest Cluster Galaxies. NGC1277
and the other Perseus core UMBH, NGC1270, have not however been able to gather
more stars or gas owing to their rapid orbital motion in the cluster core.Comment: 5 pages, 4 figures, MNRAS in pres
Major Galaxy Mergers and the Growth of Supermassive Black Holes in Quasars
Despite observed strong correlations between central supermassive black holes
(SMBHs) and star-formation in galactic nuclei, uncertainties exist in our
understanding of their coupling. We present observations of the ratio of
heavily-obscured to unobscured quasars as a function of cosmic epoch up to z~3,
and show that a simple physical model describing mergers of massive, gas-rich
galaxies matches these observations. In the context of this model, every
obscured and unobscured quasar represent two distinct phases that result from a
massive galaxy merger event. Much of the mass growth of the SMBH occurs during
the heavily-obscured phase. These observations provide additional evidence for
a causal link between gas-rich galaxy mergers, accretion onto the nuclear SMBH
and coeval star formation.Comment: Accepted for publication in Science. Published by Science Express on
March 25th. 17 pages, 5 figures, including supplemental online materia
Wage Divergence and Asymmetries in Unemployment in a Model with Biased Technical Change
In this article we assume two levels of skills and two classes of goods, one produced with a technology requiring high skills, the other produced with a technology that can be operated by both low and high skilled workers. Our model generates two distinct labour market regimes. In one regime we show technical change can be the cause of wage divergence between skilled and unskilled workers. This result is consistent with recent evidence on wage differentials. Adding the Phillips-effect shows this wage divergence can be "traded off" against unemployment of low skilled workers, and hence explains evidence on skill asymmetries in unemployment. Under the alternative regime these effects do not exist but high skilled workers may replace low skilled workers driving them out of their jobs.economics of technology ;
Observations of fast anisotropic ion heating, ion cooling, and ion recycling in large-amplitude drift waves
Large-amplitude drift wave fluctuations are observed to cause severe ion temperature oscillations in plasmas of the Caltech Encore tokamak [J. M. McChesney, P. M. Bellan, and R. A. Stern, Phys. Fluids B 3, 3370 (1991)]. Experimental investigations of the complete ion dynamical behavior in these waves are presented. The wave electric field excites stochastic ion orbits in the plane normal (perpendicular to) to B, resulting in rapid perpendicular to heating. Ion-ion collisions impart energy along (parallel to) B, relaxing the perpendicular to-parallel to temperature anisotropy. Hot ions with large orbit radii escape confinement, reaching the chamber wall and cooling the distribution. Cold ions from the plasma edge convect back into the plasma (i.e., recycle), causing further cooling and significantly replenishing the density depleted by orbit losses. The ion-ion collision period tau(ii)similar to Tau(3/2)/n fluctuates strongly with the drift wave phase, due to intense (approximate to 50%) fluctuations in n and Tau. Evidence for particle recycling is given by observations of bimodal ion velocity distributions near the plasma edge, indicating the presence of cold ions (0.4 eV) superposed atop the hot (4-8 eV) plasma background. These appear periodically, synchronous with the drift wave phase at which ion fluid flow from the wall toward the plasma center peaks. Evidence is presented that such a periodic heat/loss/recycle/cool process is expected in plasmas with strong stochastic heating
Real-time phase-selective data acquisition system for measurement of wave phenomena in pulsed plasma discharges
A novel data acquisition system and methodology have been developed for the study of wave phenomena in pulsed plasma discharges. The method effectively reduces experimental uncertainty due to shot-to-shot fluctuations in high repetition rate experiments. Real-time analysis of each wave form allows classification of discharges by wave amplitude, phase, or other features. Measurements can then be constructed from subsets of discharges having similar wave properties. The method clarifies the trade-offs between experimental uncertainty reduction and increased demand for data storage capacity and acquisition time. Finally, this data acquisition system is simple to implement and requires relatively little equipment: only a wave form digitizer and a moderately fast computer
Generalized virial theorem in Palatini gravity
We use the collision-free Boltzmann equation in Palatini
gravity to derive the virial theorem within the context of the Palatini
approach. It is shown that the virial mass is proportional to certain
geometrical terms appearing in the Einstein field equations which contribute to
gravitational energy and that such geometric mass can be attributed to the
virial mass discrepancy in cluster of galaxies. We then derive the velocity
dispersion relation for clusters followed by the metric tensor components
inside the cluster as well as the lagrangian in terms of the
observational parameters. Since these quantities may also be obtained
experimentally, the virial theorem is a convenient tool to
test the viability of theories in different models. Finally,
we discuss the limitations of our approach in the light of the cosmological
averaging used and questions that have been raised in the literature against
such averaging procedures in the context of the present work.Comment: 16 pages, to appear in PR
The virial theorem and the dynamics of clusters of galaxies in the brane world models
A version of the virial theorem, which takes into account the effects of the
non-compact extra-dimensions, is derived in the framework of the brane world
models. In the braneworld scenario, the four dimensional effective Einstein
equation has some extra terms, called dark radiation and dark pressure,
respectively, which arise from the embedding of the 3-brane in the bulk. To
derive the generalized virial theorem we use a method based on the
collisionless Boltzmann equation. The dark radiation term generates an
equivalent mass term (the dark mass), which gives an effective contribution to
the gravitational energy. This term may account for the well-known virial
theorem mass discrepancy in actual clusters of galaxies. An approximate
solution of the vacuum field equations on the brane, corresponding to weak
gravitational fields, is also obtained, and the expressions for the dark
radiation and dark mass are derived. The qualitative behavior of the dark mass
is similar to that of the observed virial mass in clusters of galaxies. We
compare our model with the observational data for galaxy clusters, and we
express all the physical parameters of the model in terms of observable
quantities. In particular, we predict that the dark mass must extend far beyond
the presently considered virial radius. The behavior of the galaxy cluster
velocity dispersion in brane world models is also considered. Therefore the
study of the matter distribution and velocity dispersion at the extragalactic
scales could provide an efficient method for testing the multi-dimensional
physical models.Comment: 29 pages, no figures, accepted for publication in PR
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