92 research outputs found
The Diverse Properties of GPS Sources
We discuss the morphology and kinematics of five gigahertz-peaked spectrum
(GPS) sources that have been observed with the VLBA. We find a wide range of
observed properties including core-jet structure, superluminal motion,
variability, extended structure, and polarization, all of which appear to
deviate from commonly-accepted GPS paradigms (e.g., O'Dea 1998). We suggest
that the observed low frequency cutoff in GPS sources may be primarily due to
free-free absorption rather than synchrotron self-absorption.Comment: Proceedings of the 6th European VLBI Network Symposium, Ros E.,
Porcas R.W., Lobanov, A.P., & Zensus, J.A. (eds), MPIfR, Bonn, Germany. (4
pages, 5 figures, needs evn2002.cls style file
VLBI imaging of extremely high redshift quasars at 5 GHz
We present very long baseline interferometry (VLBI) images of ten very high
redshift (z>3) quasars at 5 GHz. The sources 0004+139, 0830+101, 0906+041,
0938+119 and 1500+045 were observed in September 1992 using a global VLBI
array, while 0046+063, 0243+181, 1338+381, 1428+423 and 1557+032 were observed
in October 1996 with the European VLBI Network and Hartebeesthoek, South
Africa. Most of the sources are resolved and show asymmetric structure. The
sample includes 1428+423, the most distant radio loud quasar known to date
(z=4.72). It is barely resolved with an angular resolution of about 2.0*1.4
mas.Comment: Astronomy and Astrophysics, in press, Latex2e, 10 pages, 3 figures
(and lots of sub-figures
VSOP observation of the quasar PKS 2215+020: a new laboratory for core-jet physics at z=3.572
We report results of a VSOP (VLBI Space Observatory Programme) observation of
a high redshift quasar PKS 2215+020 (z=3.572). The ~1 milliarcsecond resolution
image of the quasar reveals a prominent `core-jet' structure on linear scales
from 5/h to 300/h pc ($H_0=100*h km/(s*Mpc). The brightness temperatures and
sizes of bright features identified in the jet are consistent with emission
from relativistic shocks dominated by adiabatic energy losses. The jet is
powered by the central black hole with estimated mass of ~4*10^9 solar masses.
Comparisons with VLA and ROSAT observations indicate a possible presence of an
extended radio/X-ray halo surrounding 2215+020.Comment: 15 pages, 6 figures, aastex macros; accepted for publication in The
Astrophysical Journal, V.546, N.2 *(January 10 2001
Observations of the bright radio sources in the North Celestial Pole region at the RATAN-600 radio telescope
A survey of the North Celestial Pole region using the RATAN-600 radio
telescope at five frequencies in the range 2.3 to 21.7 GHz is described.
Sources were chosen from the NVSS catalogue. The flux densities of 171 sources
in the Declination range +75 to +88 are presented; typical flux density errors
are 5-10 percent including calibration errors. About 20 percent of the sources
have flat spectra or a flat component.Comment: 21 pages, 7 figures; to be published in Astronomy and Astrophysics
(without last figure with the spectra of the observed sources
Imaging galactic diffuse gas: Bright, turbulent CO surrounding the line of sight to NRAO150
To understand the environment and extended structure of the host galactic gas
whose molecular absorption line chemistry, we previously observed along the
microscopic line of sight to the blazar/radiocontinuum source NRAO150 (aka
B0355+508), we used the IRAM 30m Telescope and Plateau de Bure Interferometer
to make two series of images of the host gas: i) 22.5 arcsec resolution
single-dish maps of 12CO J=1-0 and 2-1 emission over a 220 arcsec by 220 arcsec
field; ii) a hybrid (interferometer+singledish) aperture synthesis mosaic of
12CO J=1-0 emission at 5.8 arcsec resolution over a 90 arcsec-diameter region.
CO components that are observed in absorption at a moderate optical depth (0.5)
and are undetected in emission at 1 arcmin resolution toward NRAO 150 remain
undetected at 6 arcsec resolution. This implies that they are not a
previously-hidden large-scale molecular component revealed in absorption, but
they do highlight the robustness of the chemistry into regions where the
density and column density are too low to produce much rotational excitation,
even in CO. Bright CO lines around NRAO150 most probably reflect the variation
of a chemical process, i.e. the C+-CO conversion. However, the ultimate cause
of the variations of this chemical process in such a limited field of view
remains uncertain.Comment: 18 pages, 22 PostScript files giving 14 figures. Accepted for
publication in Astronomy & Astrophysics in the letter section. Uses aa LaTeX
macro
FIRST-based survey of Compact Steep Spectrum sources I. MERLIN images of arc-second scale objects
Compact Steep Spectrum (CSS) sources are powerful extragalactic radio sources
with angular dimensions of the order of a few arcseconds or less. Such a
compactness is apparently linked to the youth of these objects. The majority of
CSSs investigated so far have been known since the early 1980s. This paper is
the first in a series where we report the results of an observational campaign
targeted on a completely new sample of CSSs which are significantly weaker than
those investigated before. The ultimate goal of that campaign is to find out
how ``weak'' CSSs compare to ``strong'', classical ones, especially with regard
to the morphologies. Here we present an analysis of morphological and physical
properties of five relatively large sources based on MERLIN observations at 1.6
and 5 GHz.Comment: 8 pages, 7 figures, A&A in pres
Predictions for high-frequency radio surveys of extragalactic sources
We present detailed predictions of the contributions of the various source
populations to the counts at frequencies of tens of GHz. New evolutionary
models are worked out for flat-spectrum radio quasars, BL Lac objects, and
steep-spectrum sources. Source populations characterized by spectra peaking at
high radio frequencies, such as extreme GPS sources, ADAF/ADIOS sources and
early phases of gamma-ray burst afterglows are also dealt with. The counts of
different populations of star-forming galaxies (normal spirals, starbursts,
high-z galaxies detected by SCUBA and MAMBO surveys, interpreted as
proto-spheroidal galaxies) are estimated taking into account both synchrotron
and free-free emission, and dust re-radiation. Our analysis is completed by
updated counts of Sunyaev-Zeldovich effects in clusters of galaxies and by a
preliminary estimate of galactic-scale Sunyaev-Zeldovich signals associated to
proto-galactic plasma.Comment: 12 pages, 14 figures, to be published in A&
VLBA polarimetric observations of the CSS quasar 3C147
Aims. We report new VLBA polarimetric observations of the compact
steep-spectrum (CSS) quasar 3C147 (B0538+498) at 5 and 8.4GHz.
Methods. By using multifrequency VLBA observations, we derived
milliarcsecond-resolution images of the total intensity, polarisation, and
rotation measure distributions, by combining our new observations with archival
data.
Results. The source shows a one-sided structure, with a compact region, and a
component extending about 200 mas to the south-west. The compact region is
resolved into two main components with polarised emission, a complex rotation
measure distribution, and a magnetic field dominated by components
perpendicular to the source axis.
Conclusions. By considering all the available data, we examine the possible
location of the core component, and discuss two possible interpretations of the
observed structure of this source: core-jet and lobe-hot spot. Further
observations to unambiguously determine the location of the core would help
distinguish between the two possibilities discussed here.Comment: 11 pages, 12 figure
A kinematic study of the compact jet in quasar B3 1633+382
We present a study of the motion of compact jet components in quasar B3
1633+382. Through analyzing 14 epochs of VLBI observations of three components
(B1, B2, and B3) at 22 GHz, we find two different possibilities of component
classification. Thus two corresponding kinematical models can be adopted to
explain the evolutionary track of components. One is a linear motion, while
another is a helical model. Future observations are needed to provide new
kinematical constraints for the motion of these components in this source.Comment: 7 pages, 3 figures; Accepted for publication in A&
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