2,206 research outputs found
Characteristics of UGC galaxies detected by IRAS
Infrared Astronomy Satellite (IRAS) detection rates at 60 microns were determined for the Uppsala General Catalog of Galaxies (Nilson 1973; the UCG). Late-type spirals, characterized by a normal IR/B ratio of approximately 0.6, are detected to a velocity of approximately 6000 km/s for L sub B = L sub *. Contrary to the situation for IRAS-selected galaxy samples, little evidence was found for a correlation between IR/B and 60/100 microns in this large optically-selected sample. Thus a significant fraction of the IRAS-measured far-infrared flux from normal spirals must originate in the diffuse interstellar medium, heated by the interstellar radiation field. Support was not found for Burstein and Lebofsky's (1986) conclusion that spiral disks are optically thick in the far-infrared
Grid simulation services for the medical community
The first part of this paper presents a selection of medical simulation applications, including image reconstruction, near real-time registration for neuro-surgery, enhanced dose distribution calculation for radio-therapy, inhaled drug delivery prediction, plastic surgery planning and cardio-vascular system simulation. The latter two topics are discussed in some detail. In the second part, we show how such services can be made available to the clinical practitioner using Grid technology. We discuss the developments and experience made during the EU project GEMSS, which provides reliable, efficient, secure and lawful medical Grid services
A high resolution view of the jet termination shock in a hot spot of the nearby radio galaxy Pictor A: implications for X-ray models of radio galaxy hot spots
Images made with the VLBA have resolved the region in a nearby radio galaxy,
Pictor A, where the relativistic jet that originates at the nucleus terminates
in an interaction with the intergalactic medium, a so-called radio galaxy hot
spot. This image provides the highest spatial resolution view of such an object
to date (16 pc), more than three times better than previous VLBI observations
of similar objects. The north-west Pictor A hot spot is resolved into a complex
set of compact components, seen to coincide with the bright part of the hot
spot imaged at arcsecond-scale resolution with the VLA. In addition to a
comparison with VLA data, we compare our VLBA results with data from the HST
and Chandra telescopes, as well as new Spitzer data. The presence of pc-scale
components in the hot spot, identifying regions containing strong shocks in the
fluid flow, leads us to explore the suggestion that they represent sites of
synchrotron X-ray production, contributing to the integrated X-ray flux of the
hot spot, along with X-rays from synchrotron self-Compton scattering. This
scenario provides a natural explanation for the radio morphology of the hot
spot and its integrated X-ray emission, leading to very different predictions
for the higher energy X-ray spectrum compared to previous studies. From the
sizes of the individual pc-scale components and their angular spread, we
estimate that the jet width at the hot spot is in the range 70 - 700 pc, which
is comparable to similar estimates in PKS 2153-69, 3C 205, and 4C 41.17. The
lower limit in this range arises from the suggestion that the jet may dither in
its direction as it passes through hot spot backflow material close to the jet
termination point, creating a "dentist drill" effect on the inside of a cavity
700 pc in diameter.Comment: Accepted by the Astronomical Journal. 35 pages, 6 figure
On Measuring the Infrared Luminosity of Distant Galaxies with the Space Infrared Telescope Facility
The Space Infrared Telescope Facility (SIRTF) will revolutionize the study of
dust-obscured star formation in distant galaxies. Although deep images from the
Multiband Imaging Photometer for SIRTF (MIPS) will provide coverage at 24, 70,
and 160 micron, the bulk of MIPS-detected objects may only have accurate
photometry in the shorter wavelength bands due to the confusion noise.
Therefore, we have explored the potential for constraining the total infrared
(IR) fluxes of distant galaxies with solely the 24 micron flux density, and for
the combination of 24 micron and 70 micron data. We also discuss the inherent
systematic uncertainties in making these transitions. Under the assumption that
distant star-forming galaxies have IR spectral energy distributions (SEDs) that
are represented somewhere in the local Universe, the 24 micron data (plus
optical and X-ray data to allow redshift estimation and AGN rejection)
constrains the total IR luminosity to within a factor of 2.5 for galaxies with
0.4 < z < 1.6. Incorporating the 70 micron data substantially improves this
constraint by a factor < 6. Lastly, we argue that if the shape of the IR SED is
known (or well constrained; e.g., because of high IR luminosity, or low
ultraviolet/IR flux ratio), then the IR luminosity can be estimated with more
certainty.Comment: 4 pages, 3 figures (2 in color). Accepted for Publication in the
Astrophysical Journal Letters, 2002 Nov
Plausible responses to the threat of rapid sea-level rise for the Thames Estuary
This paper considers the perceptions and responses of selected stakeholders to a scenarion of rapid rise in sea-level due to the collapse of the West Antarctic ice sheet, which could produce a global rise in sea-level of 5 to 6 metres. Through a process of dialogue involving one-to one interviews and a one-day policy exercise, we addressed influences on decision-making when information is uncertain and our ability to plan, prepare for and implement effective ways of coping with this extreme scenario. Through these interactions we hoped to uncover plausible responses to the scenario and identify potential weaknesses in our current flood management approaches to dealing with such an occurrence. By undertaking this exploratory exercise we hoped to find out whether this was a feasible way to deal with such a low probability but high consequence scenario. It was the process of finding a solution that interested us rather than the technical merits of one solution over another. We were not intending to produce definitive set of recommendations on how to respond but to gain insights into the process of making a decision, specifically what influences it and what assumptions are made.Sea level rise, London
Large-scale structure in a new deep IRAS galaxy redshift survey
We present here the first results from two recently completed, fully sampled redshift surveys comprising 3703 IRAS Faint Source Survey (FSS) galaxies. An unbiased counts-in-cells analysis finds a clustering strength in broad agreement with other recent redshift surveys and at odds with the standard cold dark matter model. We combine our data with those from the QDOT and 1.2 Jy surveys, producing a single estimate of the IRAS galaxy clustering strength. We compare the data with the power spectrum derived from a mixed dark matter universe. Direct comparison of the clustering strength seen in the IRAS samples with that seen in the APM-Stromlo survey suggests b_O/b_I=1.20+/-0.05 assuming a linear, scale independent biasing. We also perform a cell by cell comparison of our FSS-z sample with galaxies from the first CfA slice, testing the viability of a linear-biasing scheme linking the two. We are able to rule out models in which the FSS-z galaxies identically trace the CfA galaxies on scales 5-20h^{-1}Mpc. On scales of 5 and 10h^{-1}Mpc no linear-biasing model can be found relating the two samples. We argue that this result is expected since the CfA sample includes more elliptical galaxies which have different clustering properties from spirals. On scales of 20h^{-1}Mpc no linear-biasing model with b_O/b_I < 1.70 is acceptable. When comparing the FSS-z galaxies to the CfA spirals, however, the two populations trace the same structures within our uncertaintie
Ultra-luminous Infrared Galaxies in Sloan Digital Sky Survey Data Release 6
Ultra-luminous infrared galaxies (ULIRGs) are interesting objects with
dramatic properties. Many efforts have been made to understand the physics of
their luminous infrared emission and evolutionary stages. However, a large
ULIRG sample is still needed to study the properties of their central black
holes (BHs), the BH-host galaxy relation, and their evolution. We identified
308 ULIRGs from the Sloan Digital Sky Survey Data Release 6, and classified
them into the NL ULIRGs (with only narrow emission lines) and the Type I ULIRGs
(with broad emission lines). About 56% of ULIRGs in our total sample show
interaction features, and this percentage is 79% for redshift z < 0.2. Optical
identifications of these ULIRGs show that the AGN percentage is at least 49%,
and the percentage increases with the infrared luminosity. We found 62 Type I
ULIRGs, and estimated their BH masses and velocity dispersions from their
optical spectra. Together with known Type I ULIRGs in the literature, a sample
of 90 Type I ULIRGs enables us to make a statistical study. We found that the
BH masses of Type I ULIRGs are typically smaller than those of PG QSOs, and
most Type I ULIRGs follow the M_{BH}-sigma relation. However, some ULIRGs with
larger Eddington ratio deviate from this relation, even the line width of the
[OIII] narrow line (NL) core or the [SII] line was used as the surrogate of
velocity dispersion. This implies that at least some ULIRGs are probably still
in the early evolution stage toward QSOs. The anti-correlation between the mass
deviation from the M_{BH}-sigma relation and the Eddington ratio supports that
the evolution of Type I ULIRGs is probably followed by the building up of the
M_{BH}-sigma relation and the evolution to the QSO phase.Comment: 46 pages, 15 figures, 2 tables; published by Ap
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