4,660 research outputs found
Radio Properties of the Shapley Concentration. III. Merging Clusters in the A3558 Complex
We present the results of a 22 cm radio survey carried out with the A3558
complex, a chain formed by the merging ACO clusters A3556-A3558-A3562 and
thetwo groups SC1327-312 and SC1323-313, located in the central region of the
complex, a chain formed by the merging ACO clusters A3556-A3558-A3562 and the
two groups SC1327-312 and SC1323-313, located in the central region of the
Shapley Concentration. The purpose of our survey is to study the effects of
cluster mergers on the statistical properties of radio galaxies and to
investigate the connection between mergers and the presence of radio halos and
relic sources. We found that the radio source counts in the A3558 complex are
consistent with the background source counts. Furthermore, we found that no
correlation exists between the local density and the radio source power, and
that steep spectrum radio galaxies are not segregated in denser optical
regions. The radio luminosity function for elliptical and S0 galaxies is
significantly lower than that for cluster type galaxies and for those not
selected to be in clusters at radio powers logP(1.4) > 22.5, implying that the
probability of a galaxy becoming a radio source above this power limit is lower
in the Shapley Concentration compared with any other environment. The detection
of a head-tail source in the centre of A3562, coupled with careful inspection
of the 20 cm NRAO VLA Sky Survey (NVSS) and of 36 cm MOST observations, allowed
us to spot two extended sources in the region between A3562 and SC1329-313,
i.e. a candidate radio halo at the centre of A3562, and low brightness extended
emission around a 14.96 magnitude Shapley galaxy.Comment: 18 pages, 14 figures. Accepted for publication on MNRA
DAD: Some historical-epistemological considerations on its judicious use
This paper deals with the pros and cons in relation to the teaching strategy imposed specifically in Italy by the COVID-19 pandemic, which has involved and continues to involve significant changes in the setting in which students and teachers interact. The approach is multidisciplinary, in that the perspective advanced is both historical and epistemological in nature. Particular attention is paid to the possibility of erecting an argumentative framework within the operational educational context as it takes place in the temporal and spatial dimensions of the school. Suggestions are provided regarding the set of \u201ctools\u201d useful for the constructive and creative management of didactic-pedagogical modalities inherent to DAD (acronym for the Italian \u201cDidattica A Distanza\u201d, i.e., distance/remote teaching and learning), including combining the quantitative facets with the necessary qualitative facets, which are expressed in the category of the \u201cbello\u201d (beautiful), thus introducing the aesthetic value. Therefore, the concept of \u201cbenessere\u201d (well-being) and that of \u201cmalessere\u201d (malaise) are associated with the concept of \u201cbellessere\u201d (beautiful-being)
BeppoSAX observations of low power radio galaxies: possible detection of obscured nuclei
We present the first results of BeppoSAX observations of a small sample of
low brightness FRI radio galaxies. The flux of all the targets is consistent
with a thermal spectrum, as due to the presence of hot intracluster gas or
galactic corona. Moreover in three sources a non thermal absorbed spectrum can
be present in the MECS spectrum at energies larger than 7 keV, while for a
fourth object a high energy flux has been detected in the PDS instrument at
energies larger than 15 keV. This component could be related to the inner AGN
surrounded by an obscuring torus.Comment: 4 pages, LateX, 3 figures (included). Uses espcrc2.sty (included). To
appear in: "The Active X-ray Sky: Results from BeppoSAX and Rossi-XTE", Rome,
Italy, 21-24 October, 1997, Eds.: L. Scarsi, H. Bradt, P. Giommi and F. Fior
IC 4200: a gas-rich early-type galaxy formed via a major merger
We present the result of radio and optical observations of the S0 galaxy IC
4200. We find that the galaxy hosts 8.5 billion solar masses of HI rotating on
a ~90 deg warped disk extended out to 60 kpc from the centre of the galaxy.
Optical spectroscopy reveals a simple-stellar-population-equivalent age of 1.5
Gyr in the centre of the galaxy and V- and R-band images show stellar shells.
Ionised gas is observed within the stellar body and is kinematically decoupled
from the stars and characterised by LINER-like line ratios.We interpret these
observational results as evidence for a major merger origin of IC 4200, and
date the merger back to 1-3 Gyr ago.Comment: Accepted for publication in Astronomy & Astrophysics; 18 pages, 13
figures; the tables of Appendix C can be downloaded at
http://www.astro.rug.nl/~pserra/IC420
The peculiar WAT NGC 2329 with Seyfert/FR I-like radio lobes
We report the complex radio properties of the radio galaxy NGC 2329 that resides in the centre of the galaxy cluster Abell 569. For this study, we have used archival data from the Very Large Array (VLA) at various resolutions and frequencies, as well as the Very Long Baseline Array (VLBA). While the wide-angle tailed (WAT) Fanaroff-Riley type I (FR I) radio morphology of the source has been discussed widely in the literature, the nature of the inner lobes has not been as widely discussed. In particular, we note that the inner lobes resemble the bubble-like radio structures observed in Seyfert galaxies. Polarization-sensitive data from the VLA clearly show magnetic field structures consistent with FR Is for the outer lobes and Seyferts for the inner lobes in NGC 2329. FR Is are classified as radio-loud (RL) active galactic nuclei (AGN) and Seyferts as radio-quiet (RQ) AGN, making this source unique. The VLBA shows a one-sided radio jet suggesting a relativistic pc-scale outflow, leading into the inner lobes. Electron lifetime estimates suggest that the outer FR I-like lobes are nearly twice as old (~45 Myr) as the inner Seyfert-like lobes (~25 Myr). Gas inflow in this merging cluster seems to have rejuvenated the AGN about ~25 Myr ago, and may have caused a change in the accretion disc state. The complex composite radio morphology of NGC 2329 suggests that the RL/RQ dichotomy is a function of time in the lifecycle of an AGN
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