6,916 research outputs found
Extragalactic radio source evolution under the dual-population unification scheme
We show that a dual-population unification scheme provides a successful
paradigm with which to describe the evolution and beaming of all bright
extragalactic radio sources. The paradigm consists of two intrinsic
radio-source populations, based on the two distinct radio-galaxy morphologies
of Fanaroff-Riley classes I and II. These represent the `unbeamed' or `side-on'
parent populations of steep radio spectra; the `beamed' source types including
flat-spectrum quasars and BL Lac objects, arise through the random alignment of
their radio-axis to our line-of-sight where Doppler-beaming of the relativistic
radio jets produces highly anisotropic radio emission.Comment: 18 pages & 18 postscript figures, accepted for publication in MNRA
Apparatus for welding torch angle and seam tracking control Patent
Computer controlled apparatus for maintaining welding torch angle and velocity during seam trackin
The correlation function of radio sources
We investigate the large-scale clustering of radio sources in the Green Bank
and Parkes-MIT-NRAO 4.85 GHz surveys by measuring the angular two-point
correlation function w(\theta). Excluding contaminated areas, the two surveys
together cover 70 per cent of the whole sky. We find both surveys to be
reasonably complete above 50 mJy. On the basis of previous studies, the radio
sources are galaxies and radio-loud quasars lying at redshifts up to z \sim 4,
with a median redshift z \sim 1. This provides the opportunity to probe
large-scale structures in a volume far larger than that within the reach of
present optical and infrared surveys. We detect a clustering signal w(\theta)
\approx 0.01 for \theta = 1\degr. By assuming an evolving power-law spatial
correlation function in comoving coordinates \xi(r_c,z) = ( r_c / r_0
)^{-\gamma} (1+z)^{\gamma-(3+\epsilon)}, where \gamma = 1.8, and the redshift
distribution N(z) of the radio galaxies, we constrain the r_0--\epsilon
parameter space. For `stable clustering' (\epsilon = 0), we find the
correlation length r_0 \approx 18 Mpc/h, larger than the value for nearby
normal galaxies and comparable to the cluster-cluster correlation length.Comment: 8 pages, 7 ps figures included, LaTeX (mn,sty). Accepted by MNRA
Evolution of AGN Space Densities and the FR Dichotomy
We focus on a comparison of the space densities of FRI and FRII extended
radio sources at different epochs, and find that FRI and FRII sources show
similar space density enhancements in various redshift ranges, possibly
implying a common evolution.Comment: IAU Symposium 267 Proceeding - 1 pag
The Deep Diffuse Extragalactic Radio Sky at 1.75 GHz
We present a study of diffuse extragalactic radio emission at GHz
from part of the ELAIS-S1 field using the Australia Telescope Compact Array.
The resulting mosaic is deg, with a roughly constant noise region
of deg used for analysis. The image has a beam size of arcsec and instrumental Jy beam. Using point-source models from the ATLAS survey, we
subtract the discrete emission in this field for Jy
beam. Comparison of the source-subtracted probability distribution, or
\pd, with the predicted distribution from unsubtracted discrete emission and
noise, yields an excess of Jy beam. Taking this as
an upper limit on any extended emission we constrain several models of extended
source counts, assuming arcmin. The best-fitting
models yield temperatures of the radio background from extended emission of
mK, giving an upper limit on the total temperature at
GHz of mK. Further modelling shows that our data are
inconsistent with the reported excess temperature of ARCADE2 to a source-count
limit of Jy. Our new data close a loop-hole in the previous
constraints, because of the possibility of extended emission being resolved out
at higher resolution. Additionally, we look at a model of cluster halo emission
and two WIMP dark matter annihilation source-count models, and discuss general
constraints on any predicted counts from such sources. Finally, we report the
derived integral count at GHz using the deepest discrete count plus our
new extended-emission limits, providing numbers that can be used for planning
future ultra-deep surveys.Comment: 18 pages, 15 figures, 7 tables, Accepted by MNRA
Variance and Skewness in the FIRST survey
We investigate the large-scale clustering of radio sources in the FIRST
1.4-GHz survey by analysing the distribution function (counts in cells). We
select a reliable sample from the the FIRST catalogue, paying particular
attention to the problem of how to define single radio sources from the
multiple components listed. We also consider the incompleteness of the
catalogue. We estimate the angular two-point correlation function ,
the variance , and skewness of the distribution for the
various sub-samples chosen on different criteria. Both and
show power-law behaviour with an amplitude corresponding a spatial correlation
length of Mpc. We detect significant skewness in the
distribution, the first such detection in radio surveys. This skewness is found
to be related to the variance through , with
, consistent with the non-linear gravitational growth of
perturbations from primordial Gaussian initial conditions. We show that the
amplitude of variance and skewness are consistent with realistic models of
galaxy clustering.Comment: 13 pages, 21 inline figures, to appear in MNRA
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