7,312 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 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
The cluster environments of the z~1 3CR radio galaxies
An analysis of the environments around a sample of 28 3CR radio galaxies with
redshifts 0.6 < z < 1.8 is presented, based primarily upon K--band images down
to K ~ 20 taken using the UK Infrared Telescope (UKIRT). A net overdensity of
K-band galaxies is found in the fields of the radio galaxies, with the mean
excess counts being comparable to that expected for clusters of Abell Class 0
richness. A sharp peak is found in the angular cross-correlation amplitude
centred on the radio galaxies, which, for reasonable assumptions about the
luminosity function of the galaxies, corresponds to a spatial cross-correlation
amplitude between those determined for low redshift Abell Class 0 and Abell
Class 1 clusters.Comment: 18 pages LaTeX, including 10 figures. Accepted for publication in
MNRA
A jet-cloud interaction in 3C34 at redshift z = 0.69
We report the detection of a strong jet-cloud interaction at a distance of
120 kpc from the nucleus of the radio galaxy 3C34, which has redshift z=0.69.
Hubble Space Telescope images of the radio galaxy show a long narrow region of
blue emission orientated along the radio axis and directed towards a radio
hotspot. The William Herschel Telescope has been used to provide long-slit
spectroscopic data of this object, and infrared observations made with the
United Kingdom InfraRed Telescope have enabled its spectral energy distribution
to be modelled. We propose that the aligned emission is associated with a
region of massive star-formation, induced by the passage of the radio jet
through a galaxy within the cluster surrounding 3C34. A star-formation rate of
about 100 solar masses per year is required, similar to the values necessary to
produce the alignment effect in high-redshift radio galaxies. The consequences
of this result for models of star formation in distant radio galaxies are
discussed.Comment: 12 pages including 11 figures, LaTeX. To appear in MNRA
HST, radio and infrared observations of 28 3CR radio galaxies at redshift z ~ 1: I. The observations
Hubble Space Telescope images are presented of a sample of 28 3CR radio
galaxies with redshifts in the range 0.6 < z < 1.8, together with maps at
comparable angular resolution of their radio structure, taken using the Very
Large Array. Infrared images of the fields, taken with the United Kingdom
InfraRed Telescope, are also presented. The optical images display a
spectacular range of structures. Many of the galaxies show highly elongated
optical emission aligned along the directions of the radio axes, but this is
not a universal effect; a small number of sources are either symmetrical or
misaligned. Amongst those sources which do show an alignment effect, the
morphology of the optical emission varies greatly, from a single bright
elongated emission region to strings of optical knots stretching from one radio
hotspot to the other. The infrared images display much less complexity.
Although their significantly lower angular resolution would wash out some of
the smaller structures seen in the HST images, it is clear that these galaxies
are less aligned at infrared wavelengths than in the optical. In this paper, we
discuss the galaxies individually, but defer a statistical analysis of the
multi-waveband properties of the complete sample of sources to later papers in
this series.Comment: 39 pages including 52 figures, LaTeX. Accepted for publication in
MNRA
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