196 research outputs found
Nearby radio loud AGN and the Unified Model
The statistical study of the parsec scale properties of radio sources is
crucial to get information on the nature of the central engine and to provide
the foundations of the current unified theories, suggesting that the appearance
of active galactic nuclei depends strongly on orientation. We started a project
to observe at sub-arcsec resolution a complete sample of 94 nearby (z<0.1)
radio galaxies, the Bologna Complete Sample, which is not affected by any
selection effect on the jet velocity and orientation with respect to the line
of sight. Up to now, we published our parsec scale analysis of 77/94 sources.
Here, we describe the last VLBA observations at 5 GHz and EVN data at 18 cm
obtained for the 17 remaining faintest radio core (<5 mJy at 5 GHz in VLA
images) BCS sources and we report our preliminary results on the whole complete
sample.Comment: 4 pages, 1 figure; accepted for publication in the proceeding of the
"12th European VLBI Network Symposium and Users Meeting - EVN 2014" (7-10
October 2014, Cagliari, Italy); published online in Proceedings of Science,
PoS(EVN 2014)09
VLBI observations of nearby radio loud Active Galactic Nuclei
We present an update of the parsec scale properties of the Bologna Complete
Sample consisting of 95 radio sources from the B2 Catalog of Radio Sources and
the Third Cambridge Revised Catalog (3CR), with z < 0.1. Thanks to recent new
data we have now parsec scale images for 76 sources of the sample. Most of them
show a one-sided jet structure but we find a higher fraction of two-sided
sources in comparison with previous flux-limited VLBI surveys. A few peculiar
sources are presented and discussed in more detail.Comment: 6 pages, 7 figures, Proceedings for "The Universe under the
Microscope" (AHAR 2008), April 2008, to be published in Journal of Physics:
Conference Series by Institute of Physics Publishing; R. Schoedel, A. Eckart,
S. Pfalzner, and E. Ros ed
Twin SMBH candidates in the BCG of RBS 797
The radio-loud BCG at the center of the cool core cluster RBS 797 is known to
exhibit a misalignment of its 5 GHz radio emission observed at different VLA
resolutions, with the innermost kpc-scale jets being almost orthogonal to the
radio lobes which extends for tens of kpc filling the X-ray cavities seen by
Chandra. The different radio directions may be caused by rapid jet
reorientation due to interaction with a secondary supermassive black hole
(SMBH), or to the presence of two AGN, probably in a merging phase, which are
emitting radio jets in different directions. We present the results of new 5
GHz observations performed with the EVN in May 2013. In particular, we detected
two compact radio components, with a projected separation of 77 pc. We discuss
two possible scenarios for the origin and nature of the EVN double source,
showing that both interpretations are consistent with the presence of a SMBH
binary system in the BCG of RBS 797.Comment: 4 pages, 1 figure; accepted for publication in the proceeding of the
"12th European VLBI Network Symposium and Users Meeting - EVN 2014" (7-10
October 2014, Cagliari, Italy); published online in Proceedings of Science,
PoS(EVN 2014)08
e-EVN monitoring of M87
M87 is a privileged laboratory for a detailed study of the properties of jets, owing to its proximity (D=16.7 Mpc, 1 mas = 0.080 pc), its massive black hole (~6.0 x 10^9M) and its conspicuous emission at radio wavelengths and above. We started on November 2009 a monitoring program with the e-EVN at 5 GHz, in correspondence of the season of Very High Energy (VHE) observations. Indeed, two episodes of VHE activity have been reported in February and April 2010. We present here the main results of these multi-epoch observations: the inner jet and HST-1 are both detected and resolved in our datasets. We study the apparent velocity of HST-1, which seems to be increasing since 2005, and the flux density variability in the inner jet. All in all, the radio counterpart to this year’s VHE event seems to be different from the ones in 2005 and 2008, opening new scenario for the radio-high energy connection
Evidence for nuclear radio jet and its structure down to <100 Schwarzschild radii in the center of the Sombrero galaxy (M 104, NGC 4594)
Abridged: We investigated the detailed radio structure of the nucleus of the
Sombrero galaxy using high-resolution, quasi-simultaneous, multi-frequency,
phase-referencing VLBA observations. We obtained the VLBI images toward this
nucleus, with unprecedented sensitivities and resolutions, at the seven
frequencies between 1.4 and 43 GHz, where those at 15, 24 and 43 GHz are the
first clear VLBI detections. At 43 GHz, the nuclear structure was imaged on a
linear scale under 100 Schwarzschild radii. For the first time, we have
discovered the presence of the extended structure in this nucleus, which is
directing from the radio core in two sides toward northwest/southeast
directions. The nuclear structure shows a clear spatial gradient on the radio
spectra, which is similar to that commonly seen in more luminous AGN with
powerful relativistic jets. Moreover, the radio core shows a
frequency-dependent size with an elongated shape, and the position of the core
also tends to be frequency dependent. A set of these new findings provide
evidence that the central engine of the Sombrero is powering radio jets. Based
on the observed brightness ratio of jet-to-counter jet, core position shift and
its comparison with a theoretical model, we constrained the following
fundamental physical parameters for the M 104 jets: (1) the northern side is
the approaching jet, whereas the southern side is receding: (2) the inclination
angle of the jet is relatively close to our line-of-sight, probably less than
~25degrees: (3) the jet intrinsic velocity is highly sub-relativistic at a
speed less than ~0.2c. The derived pole-on nature of the M 104 jet is in
accordance with the previous argument that M 104 contains a true type II AGN,
i.e., the broad line region of this nucleus is actually absent or intrinsically
weak, if the plane of the presumed circumnuclear torus is perpendicular to the
axis of the radio jets.Comment: 12 pages, 9 figures, 4 tables, accepted for publication in Ap
Molecular gas and nuclear activity in early-type galaxies: any link with radio-loudness?
Aims. We want to study the amount of molecular gas in a sample of nearby
early-type galaxies (ETGs) which host low-luminosity Active Galactic Nuclei
(AGN). We look for possible differences between the radio-loud (RL) and
radio-quiet (RQ) AGN. Methods. We observed the CO(1-0) and CO(2-1) spectral
lines with the IRAM 30m and NRO 45m telescopes for eight galaxies. They belong
to a large sample of 37 local ETGs which host both RQ and RL AGN. We gather
data from the literature for the entire sample. Results. We report the new
detection of CO(1-0) emission in four galaxies (UGC0968, UGC5617, UGC6946, and
UGC8355) and CO(2-1) emission in two of them (UGC0968 and UGC5617). The
CO(2-1)/CO(1-0) ratio in these sources is . Considering both the
new observations and the literature, the detection rate of CO in our sample is
55 9%, with no statistically significant difference between the hosts of
RL and RQ AGNs. For all the detected galaxies we converted the CO luminosities
into the molecular masses, , that range from 10 to 10
M, without any statistically significant differences between RL and
RQ galaxies. This suggests that the amount of molecular gas does not likely set
the radio-loudness of the AGN. Furthermore, despite the low statistical
significance, the presence of a weak trend between the H mass with
various tracers of nuclear activity (mainly [O III] emission line nuclear
power) cannot be excluded.Comment: Accepted for publication on A&A, 9 pages, 5 figure
A sensitive study of the peculiar jet structure HST-1 in M87
To obtain a better understanding of the location and mechanisms for the
production of the gamma-ray emission in jets of AGN we present a detailed study
of the HST-1 structure, 0.8 arcsec downstream the jet of M87, previously
identified as a possible candidate for TeV emission. HST-1 shows a very
peculiar structure with superluminal as well as possible stationary
sub-components, and appears to be located in the transition from a parabolic to
a conical jet shape, presumably leading to the formation of a recollimation
shock. This scenario is supported by our new RHD simulations in which the
interaction of a moving component with a recollimation shock leads to the
appearance of a new superluminal component. To discern whether HST-1 is
produced by a recollimation shock or some other MHD instability, we present new
polarimetric 2.2 and 5 GHz VLBA, as well as 15, 22 and 43 GHz JVLA observations
obtained between November 2012 and March 2013.Comment: 6 page
Growth Impairment and Nutritional Deficiencies in a Cow's Milk-Allergic Infant Fed by Unmodified Donkey's Milk
We report a case of growth impairment and nutritional deficiencies in a five-month infant fed by unmodified donkey's milk. We discuss the energy and macronutrient daily intake from donkey's milk and the nutritional consequences that can occur if this kind of milk is used unmodified in the first year of life
- …