3,049 research outputs found
Detection of X-ray emission from the host clusters of 3CR quasars
We report the detection of extended X-ray emission around several powerful
3CR quasars with redshifts out to 0.73. The ROSAT HRI images of the quasars
have been corrected for spacecraft wobble and compared with an empirical
point-spread function. All the quasars examined show excess emission at radii
of 15 arcsec and more; the evidence being strong for the more distant objects
and weak only for the two nearest ones, which are known from other wavelengths
not to lie in strongly clustered environments. The spatial profiles of the
extended component is consistent with thermal emission from the intracluster
medium of moderately rich host clusters to the quasars. The total luminosities
of the clusters are in the range 4x10^44 - 3x10^45 erg/s, assuming a
temperature of 4keV. The inner regions of the intracluster medium are, in all
cases, dense enough to be part of a cooling flow.Comment: 21 pages including 4 figures and 4 tables. To be published in MNRA
A Parkes half-Jansky sample of GPS galaxies
This paper describes the selection of a new southern/equatorial sample of
Gigahertz Peaked Spectrum (GPS) radio galaxies, and subsequent optical CCD
imaging and spectroscopic observations using the ESO 3.6m telescope. The sample
consists of 49 sources with -4020 degrees, and
S(2.7GHz)>0.5 Jy, selected from the Parkes PKSCAT90 survey. About 80% of the
sources are optically identified, and about half of the identifications have
available redshifts. The R-band Hubble diagram and evolution of the host
galaxies of GPS sources are reviewed.Comment: Latex, 12 pages, 8 figures, accepted for publication in MNRA
Conception and preliminary evaluation of an optical fibre sensor for simultaneous measurement of pressure and temperature
peer-reviewedThis paper presents a novel concept of simultaneously measuring pressure and
temperature using a silica optical fibre extrinsic Fabry-Perot interferometric (EFPI) pressure
sensor incorporating a fibre Bragg grating (FBG), which is constructed entirely from fusedsilica.
The novel device is used to simultaneously provide accurate pressure and temperature
readings at the point of measurement. Furthermore, the FBG temperature measurement is used
to eliminate the temperature cross-sensitivity of the EFPI pressure sensorPUBLISHEDpeer reviewe
Massive galaxies with very young AGN
Gigahertz Peaked Spectrum (GPS) radio galaxies are generally thought to be
the young counterparts of classical extended radio sources and live in massive
ellipticals. GPS sources are vital for studying the early evolution of
radio-loud AGN, the trigger of their nuclear activity, and the importance of
feedback in galaxy evolution. We study the Parkes half-Jansky sample of GPS
radio galaxies of which now all host galaxies have been identified and 80% has
their redshifts determined (0.122 < z < 1.539). Analysis of the absolute
magnitudes of the GPS host galaxies show that at z > 1 they are on average a
magnitude fainter than classical 3C radio galaxies. This suggests that the AGN
in young radio galaxies have not yet much influenced the overall properties of
the host galaxy. However their restframe UV luminosities indicate that there is
a low level of excess as compared to passive evolution models.Comment: To appear in the proceedings of "Formation and Evolution of Galaxy
Bulges", IAUS 245; M. Bureau, E. Athanassoula & B. Barbuy, ed
Faint Gigahertz peaked spectrum sources and the evolution of young radio sources
GPS sources are the objects of choice to study the initial evolution of
extragalactic radio sources, since it is most likely that they are the young
counterparts of large scale radio sources. Correlations found between their
peak frequency, peak flux density and angular size provide strong evidence that
synchrotron self absorption is the cause of the spectral turnovers, and
indicate that young radio sources evolve in a self-similar way. The difference
in redshift distribution between young and old radio sources must be due to a
difference in slope of their luminosity functions, and we argue that this slope
is strongly affected by the luminosity evolution of the individual sources. A
luminosity evolution scenario is proposed in which GPS sources increase in
luminosity and large scale radio sources decrease in luminosity with time. It
is shown that such a scenario agrees with the local luminosity function of GPS
galaxies.Comment: Late, 6 pages, 2 figs. To appear in the proceedings of EVN/JIVE
Symposium No 4, New Astronomy Reviews (eds. Garrett et al.). For related
papers, see http://www.ast.cam.ac.uk/~snelle
A new sample of faint Gigahertz Peaked Spectrum radio sources
The Westerbork Northern Sky Survey (WENSS) has been used to select a sample
of Gigahertz Peaked Spectrum (GPS) radio sources at flux densities one to two
orders of magnitude lower than bright GPS sources investigated in earlier
studies. Sources with inverted spectra at frequencies above 325 MHz have been
observed with the WSRT at 1.4 and 5 GHz and with the VLA at 8.6 and 15 GHz to
select genuine GPS sources. This has resulted in a sample of 47 GPS sources
with peak frequencies ranging from ~500 MHz to >15 GHz, and peak flux densities
ranging from ~40 to ~900 mJy. Counts of GPS sources in our sample as a function
of flux density have been compared with counts of large scale sources from
WENSS scaled to 2 GHz, the typical peak frequency of our GPS sources. The
counts can be made similar if the number of large scale sources at 2 GHz is
divided by 250, and their flux densities increase by a factor of 10. On the
scenario that all GPS sources evolve into large scale radio sources, these
results show that the lifetime of a typical GPS source is ~250 times shorter
than a typical large scale radio source, and that the source luminosity must
decrease by a factor of ~10 in evolving from GPS to large scale radio source.
However, we note that the redshift distributions of GPS and large scale radio
sources are different and that this hampers a direct and straightforward
interpretation of the source counts. Further modeling of radio source evolution
combined with cosmological evolution of the radio luminosity function for large
sources is required.Comment: LaTeX, 15 pages, 8 figs. To be published in A&AS. For more info see
http://www.ast.cam.ac.uk/~snelle
5 year Global 3-mm VLBI survey of Gamma-ray active blazars
The Global mm-VLBI Array (GMVA) is a network of 14 3\,mm and 7\,mm capable
telescopes spanning Europe and the United States, with planned extensions to
Asia. The array is capable of sensitive maps with angular resolution often
exceeding 50\,as. Using the GMVA, a large sample of prominent -ray
blazars have been observed approximately 6 monthly from later 2008 until now.
Combining 3\,mm maps from the GMVA with near-in-time 7\,mm maps from the
VLBA-BU-BLAZAR program and 2\,cm maps from the MOJAVE program, we determine the
sub-pc morphology and high frequency spectral structure of -ray
blazars. The magnetic field strength can be estimated at different locations
along the jet under the assumption of equipartition between magnetic field and
relativistic particle energies. Making assumptions on the jet magnetic field
configuration (e.g. poloidal or toroidal), we can estimate the separation of
the mm-wave "core" and the jet base, and estimate the strength of the magnetic
field there. The results of this analysis show that on average, the magnetic
field strength decreases with a power-law , .
This suggests that on average, the mm-wave "core" is \,pc downstream
of the de-projected jet apex and that the magnetic field strength is of the
order \,kG, broadly consistent with the predictions of
magnetic jet launching (e.g. via magnetically arrested disks (MAD)).Comment: 6 pages, 1 figur
Detecting the Cold Spot as a Void with the Non-Diagonal Two-Point Function
The anomaly in the Cosmic Microwave Background known as the "Cold Spot" could
be due to the existence of an anomalously large spherical (few hundreds Mpc/h
radius) underdense region, called a "Void" for short. Such a structure would
have an impact on the CMB also at high multipoles l through Lensing. This would
then represent a unique signature of a Void. Modeling such an underdensity with
an LTB metric, we show that the Lensing effect leads to a large signal in the
non-diagonal two-point function, centered in the direction of the Cold Spot,
such that the Planck satellite will be able to confirm or rule out the Void
explanation for the Cold Spot, for any Void radius with a Signal-to-Noise ratio
of at least O(10).Comment: v1: 6 pages, 2 figures; v2: 6 pages, 2 figures, text improved, to
appear on JCA
PKS2250-41: a case study for triggering
We present the results of a multiwavelength study of the z = 0.31 radio
source PKS2250-41. Integral field unit and long-slit spectroscopy obtained
using VIMOS and FORS1 on the VLT, and archival HST optical imaging observations
are used to study the morphology, kinematics and ionisation state of the
extended emission line region (EELR) surrounding this source, and also a
companion galaxy at a similar redshift. Near-infrared imaging observations
obtained using the NTT are used to analyse the underlying galaxy morphologies.
The EELR displays a complex variety of different gas kinematics and ionization
states, consistent with a mixture of radio source shocks and AGN
photoionization. The radio galaxy is likely to lie within a group environment,
and is plausibly undergoing interactions with one or more other objects. The
disk-like galaxy to the northeast of the radio source lies at a similar
redshift to the radio galaxy itself, and has its major axis position angle
aligned with the filamentary continuum and line emission extending outwards
from the radio galaxy. This filamentary structure is most plausibly interpreted
as a tidal structure associated with an interaction involving the radio source
host galaxy and the aligned companion galaxy to the north-east; this encounter
may have potentially triggered the current epoch of radio source activity.
Overall, PKS2250-41 displays some of the best evidence that radio source
activity can be triggered in this manner. [abridged]Comment: 16 pages, 13 figures (some colour). Accepted for publication in
MNRAS. Abstract abridge
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