12,918 research outputs found
An excess of sub-millimetre sources towards z~1 clusters
Deep sub-millimetre observations using SCUBA are presented of the central
regions of four high redshift clusters which have been extensively studied
optically: CL0023+0423 (z=0.84), J0848+4453 (z=1.27), CL1604+4304 (z=0.90) and
CL1604+4321 (z=0.92). 10 sub-millimetre sources are securely detected towards
these four clusters at 850 microns, with two further tenuous detections; the
raw 850 micron source counts exceed those determined from blank-field surveys
by a factor of 3-4. In particular, towards CL1604+4304, 6 sources are detected
with S(850) > 4 mJy making this the richest sub-mm field discovered to date.
Corrections for gravitational lensing by these high redshift clusters reduce
these excess sources counts, but are unlikely to account for more than about
half of the excess, with the remainder presumably directly associated with
cluster galaxies. The 450 to 850 micron flux density ratios of the detected
sources are systematically higher (at a significance level > 98%) than those
determined for blank-field selected sources, consistent with them being at the
cluster redshifts. If subsequent identifications confirm cluster membership,
these results will demonstrate that the optical Butcher-Oemler effect is also
observed at sub-mm wavelengths.Comment: MNRAS, in consideration. 11 pages, including 6 figures. Minor typos
correcte
The phase-space structure of the Klein-Gordon field
The formalism based on the equal-time Wigner function of the two-point
correlation function for a quantized Klein--Gordon field is presented. The
notion of the gauge-invariant Wigner transform is introduced and equations for
the corresponding phase-space calculus are formulated. The equations of motion
governing the Wigner function of the Klein--Gordon field are derived. It is
shown that they lead to a relativistic transport equation with electric and
magnetic forces and quantum corrections. The governing equations are much
simpler than in the fermionic case which has been treated earlier. In addition
the newly developed formalism is applied towards the description of spontaneous
symmetry breakdown.Comment: 27 pages, LaTeX, UFTP 317/199
Simulation of Field Theories in Wavelet Representation
The field is expanded in a wavelet series and the wavelet coefficients are
varied in a simulation of the 2D field theory. The drastically reduced
autocorrelations result in a substantial decrease of computing requirements,
compared to those in local Metropolis simulations. A large part of the
improvement is shown to be the result of an additional freedom in the choice of
the allowed range of change at the Metropolis update of wavelet components,
namely the range can be optimized independently for all wavelet sizes.Comment: 10 pages, LaTeX with 8 figures, Swansea preprint SWAT/3
Validation of the performance of the Aquantic 2100A fish counter
This report looks at the validation of the performance of the Logie 2100A fish counter which was carried out at Forge Weir (River Lune) and Gunnislake Fish Pass (River Tamar), using a video recording system
The triggering probability of radio-loud AGN: A comparison of high and low excitation radio galaxies in hosts of different colors
Low luminosity radio-loud active galactic nuclei (AGN) are generally found in
massive red elliptical galaxies, where they are thought to be powered through
gas accretion from their surrounding hot halos in a radiatively inefficient
manner. These AGN are often referred to as "low-excitation" radio galaxies
(LERGs). When radio-loud AGN are found in galaxies with a young stellar
population and active star formation, they are usually high-power
radiatively-efficient radio AGN ("high-excitation", HERG). Using a sample of
low-redshift radio galaxies identified within the Sloan Digital Sky Survey
(SDSS), we determine the fraction of galaxies that host a radio-loud AGN,
, as a function of host galaxy stellar mass, , star formation
rate, color (defined by the 4000 \angstrom break strength), radio luminosity
and excitation state (HERG/LERG).
We find the following: 1. LERGs are predominantly found in red galaxies. 2.
The radio-loud AGN fraction of LERGs hosted by galaxies of any color follows a
power law. 3. The fraction of red galaxies
hosting a LERG decreases strongly for increasing radio luminosity. For massive
blue galaxies this is not the case. 4. The fraction of green galaxies hosting a
LERG is lower than that of either red or blue galaxies, at all radio
luminosities. 5. The radio-loud AGN fraction of HERGs hosted by galaxies of any
color follows a power law. 6. HERGs have a
strong preference to be hosted by green or blue galaxies. 7. The fraction of
galaxies hosting a HERG shows only a weak dependence on radio luminosity cut.
8. For both HERGs and LERGs, the hosting probability of blue galaxies shows a
strong dependence on star formation rate. This is not observed in galaxies of a
different color.[abridged]Comment: 7 pages, 6 figure
The Search for AGN in Distant Galaxy Clusters
We are undertaking the first systematic study of the prevalence of AGN
activity in a large sample of high redshift galaxy clusters. Local clusters
contain mainly red elliptical galaxies, and have little or no luminous AGN
activity. However, recent studies of some moderate to high redshift clusters
have revealed significant numbers of luminous AGN within the cluster. This
effect may parallel the Butcher-Oemler effect - the increase in the fraction of
blue galaxies in distant clusters compared to local clusters. Our aim is to
verify and quantify recent evidence that AGN activity in dense environments
increases with redshift, and to evaluate the significance of this effect. As
cluster AGN are far less prevalent than field sources, a large sample of over
120 cluster fields at z > 0.1 has been selected from the Chandra archives and
is being analysed for excess point sources. The size of the excess, the radial
distribution and flux of the sources and the dependence of these on cluster
redshift and luminosity will reveal important information about the triggering
and fueling of AGN.Comment: 2 pages, to appear in proceedings of 'Multi-wavelength AGN surveys',
Cozumel, 200
- …