40 research outputs found
Brightest Cluster Galaxies in the Extended GMRT radio halo cluster sample. Radio properties and cluster dynamics
Brightest Cluster Galaxies (BCGs) show exceptional properties over the whole
electromagnetic spectrum. Their special location at the centres of galaxy
clusters raises the question of the role of the environment on their radio
properties. To decouple the effect of the galaxy mass and of the environment in
their statistical radio properties, we investigate the possible dependence of
the occurrence of radio loudness and of the fractional radio luminosity
function on the dynamical state of the hosting cluster. We studied the radio
properties of the BCGs in the Extended GMRT Radio Halo Survey (EGRHS). We
obtained a statistical sample of 59 BCGs, which was divided into two classes,
depending on the dynamical state of the host cluster, i.e. merging (M) and
relaxed (R). Among the 59 BCGs, 28 are radio-loud, and 31 are radio--quiet. The
radio-loud sources are located favourably located in relaxed clusters (71\%),
while the reverse is true for the radio-quiet BCGs, mostly located in merging
systems (81\%). The fractional radio luminosity function (RLF) for the BCGs is
considerably higher for BCGs in relaxed clusters, where the total fraction of
radio loudness reaches almost 90\%, to be compared to the 30\% in merging
clusters. For relaxed clusters, we found a positive correlation between the
radio power of the BCGs and the strength of the cool core, consistent with
previous studies on local samples. Our study suggests that the radio loudness
of the BCGs strongly depends on the cluster dynamics, their fraction being
considerably higher in relaxed clusters. We compared our results with similar
investigations, and briefly discussed them in the framework of AGN feedback.Comment: 12 pages, 6 figures, 3 tables, A&A accepte
Low frequency follow up of radio halos and relics in the GMRT Radio Halo Cluster Survey
We performed GMRT low frequency observations of the radio halos, relics and
new candidates belonging to the GMRT Radio Halo Cluster Sample first observed
at 610 MHz. High sensitivity imaging was performed using the GMRT at 325 MHz
and 240 MHz. The properties of the diffuse emission in each cluster were
compared to our 610 MHz images and/or literature information available at other
frequencies, in order to derive the integrated spectra over a wide frequency
range.Beyond the classical radio halos, whose spectral index is in the
range (S), we found sources with
. This result supports the idea that the spectra of the
radiating particles in radio halos is not universal, and that inefficient
mechanisms of particle acceleration are responsible for their origin. We also
found a variety of brightness distributions, i.e. centrally peaked as well as
clumpy halos. Even though the thermal and relativistic plasma tend to occupy
the same cluster volume, in some cases a positional shift between the radio and
X-ray peaks of emission is evident. Our observations also revealed the
existence of diffuse cluster sources which cannot be easily classified either
as halos or relics. New candidate relics were found in A1300 and in A1682, and
in some clusters "bridges" of radio emission have been detected, connecting the
relic and radio halo emission. Combining our new data with literature
information, we derived the LogL-LogP correlation for
radio halos, and investigated the possible trend of the spectral index of radio
halos with the temperature of the intracluster medium.Comment: 19 pages, 10 figures, 5 tables, accepted for publication on A&
EVN observations of candidate Compact Symmetric Objects
We present pc-scale images of ten Compact Symmetric Objects (CSO) candidates
observed with the European VLBI network (EVN). Five radio sources have been
observed at 1.6 GHz, and five more at 2.3/8.4 GHz, the latter subsample with
the inclusion in the VLBI array of 3 antennae normally used for geodesy. These
objects were selected from existing samples of GHz Peaked Spectrum (GPS) radio
sources with the purpose to find and/or confirm the CSO classification. These
new VLBI observations allow us to confirm the classification of two CSO
candidates, and to find a few new ones. The association of GPS radio galaxies
with a CSO morphology is strengthened by our findings, and this result suggests
an efficient way to increase the number of known CSOs by means of VLBI
observations of compact radio galaxies showing a convex radio spectrum.Comment: 12 pages, 9 figures, accepted for publication on A&
Effects of different architectural solutions on the thermal behaviour in an unconditioned rural building. The case of an Italian winery
Referring to the wine sector, in the Mediterranean area, most of the wine farms make use of unconditioned above-ground buildings constructed without a specific attention to temperature control, where indoor temperatures easily show trends in disagreement with correct wine-ageing and conservation. Moreover the suitable temperature ranges can differ from wine to wine, and are considerably different from ideal temperatures for human comfort. This study aimed at testing the effectiveness of different architectural elements in improving the thermal behaviour of unconditioned farm buildings, by means of energy simulations validated on an Italian case-study, comparing the data provided by the simulations with different temperature ranges. Results showed the building thermal performance depends on the chosen intervals,
some solution played negative or positive role according to the analysed range and in general roof and wall interventions were more effective than orientation and solar shading, and the combination of more strategies allow to achieve improved results
Discovery of a radio relic in the low mass, merging galaxy cluster PLCK G200.9-28.2
Radio relics at the peripheries of galaxy clusters are tracers of the elusive
cluster merger shocks. We report the discovery of a single radio relic in the
galaxy cluster PLCK G200.9-28.2 (, ) using the Giant Metrewave Radio Telescope at 235 and 610 MHz and
the Karl G. Jansky Very Large Array at 1500 MHz. The relic has a size of Mpc, an arc-like morphology and is located at 0.9 Mpc from the
X-ray brightness peak in the cluster. The integrated spectral index of the
relic is . The spectral index map between 235 and 610 MHz shows
steepening from the outer to the inner edge of the relic in line with the
expectation from a cluster merger shock. Under the assumption of diffusive
shock acceleration, the radio spectral index implies a Mach number of
for the shock. The analysis of archival XMM Newton data shows that
PLCK G200.9-28.2 consists of a northern brighter sub-cluster, and a southern
sub-cluster in a state of merger. This cluster has the lowest mass among the
clusters hosting single radio relics. The position of the Planck Sunyaev
Ze'ldovich effect in this cluster is offset by 700 kpc from the X-ray peak in
the direction of the radio relic, suggests a physical origin for the offset.
Such large offsets in low mass clusters can be a useful tool to select
disturbed clusters and to study the state of merger.Comment: 10 pages, 7 figures, 4 tables. Accepted for publication in MNRA
IGR J14488-4008: an X-ray peculiar giant radio galaxy discovered by INTEGRAL
In this paper we report the discovery and detailed radio/X-ray analysis of a
peculiar giant radio galaxy (GRG) detected by INTEGRAL, IGR J14488-4008. The
source has been recently classified as a Seyfert 1.2 galaxy at redshift 0.123;
the radio data denote the source to be a type II Fanaroff-Riley radio galaxy,
with a linear projected size exceeding 1.5 Mpc, clearly assigning IGR
J14488-4008 to the class of GRG. In the X-rays, the source shows a remarkable
spectrum, characterised by absorption by ionised elements, a characteristic so
far found in only other four broad line radio galaxies.Comment: 7 pages, 3 tables, 5 figures. Accepted for publication on MNRA
Parsec--scale radio jets in gamma--ray loud sources
We will present a multiepoch study of the three blazars 0954+658 (BL--Lac),
PKS1510--089 (HPQ) and 1749+096 (BL--Lac). The first two sources are known to
be --ray loud. Our study is based on milliarcsecond resolution
polarimetric observations carried out with the VLBA at 8.4 GHz. The
observations took place between January 1999 and May 2001. Superluminal motion
is detected along the jet of PKS1510--089 and 1749+096, with for all features. Magnetic field structure is revealed along the jets of
0954+658 and PKS 1510--089. The polarisation properties of the parsec--scale
jets remain stationary in all sources, regardless of their total flux density
variability in the radio band and of the presence of superluminal features.Comment: 4 pages, 3 figures, to appear in the proceedings of the connference
"Relativistic jets in the Chandra and XMM era", Bologna, 23-27/9/02 (New
Astr. Rev.
The space density of z>4 blazars
High redshift blazars are an important class of Active Galactic Nuclei (AGN)
that can provide an independent estimate of the supermassive black-hole mass
function in high redshift radio-loud AGN without the bias due to absorption
along the line-of-sight. Using the Cosmic Lens All Sky Survey (CLASS) we built
a complete radio flux-limited sample of high redshift (z>4) blazars suitable
for statistical studies. By combining dedicated optical observations and the
SDSS spectroscopic database, we obtained a sample of 26 blazar candidates with
a spectroscopic redshift above 4. On the basis of their radio spectrum we
distinguish between blazars and QSO with a Gigahertz Peaked Spectrum (GPS) like
spectrum. Out of the 18 confirmed blazars 14 constitute a completely
identified, flux-limited sample down to a magnitude of 21 (AB). Using this
complete sample we derive a space density of blazars with 4<z<5.5 of rho=0.13
(+0.05,-0.03) Gpc^-3. This is the first actual estimate of the blazar space
density in this range of redshift. This value is in good agreement with the
extrapolation of the luminosity function and cosmological evolution based on a
sample of flat-spectrum radio quasars selected at lower redshifts and it is
consistent with a cosmological evolution peaking at z2 similar to
radio-quiet QSO. We do not confirm, instead, the presence of a peak at z~4 in
the space density evolution, recently suggested using an X-ray selected sample
of blazars. It is possible that this extreme peak of the evolution is present
only among the most luminous blazars.Comment: 14 pages, accepted for publication on MNRAS
(https://doi.org/10.1093/mnras/sty3526