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Powerful Radio Sources (powerful + radio_source)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

The extraordinary radio galaxy MRC B1221,423: probing deeper at radio and optical wavelengths

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2010
Helen M. Johnston
ABSTRACT We present optical spectra and high-resolution multiwavelength radio observations of the compact steep-spectrum radio source MRC B1221,423 (z= 0.1706). MRC B1221,423 is a very young (,105 yr), powerful radio source which is undergoing a tidal interaction with a companion galaxy. We find strong evidence of interaction between the active galactic nucleus (AGN) and its environment. The radio morphology is highly distorted, showing a dramatic interaction between the radio jet and the host galaxy, with the jet being turned almost back on itself. H i observations show strong absorption against the nucleus at an infall velocity of ,250 km s,1 compared to the stellar velocity, as well as a second, broader component which may represent gas falling into the nucleus. Optical spectra show that star formation is taking place across the whole system. Broad optical emission lines in the nucleus show evidence of outflow. Our observations confirm that MRC B1221,423 is a young radio source in a gas-rich nuclear environment, and that there was a time delay of a few times 100 Myr between the onset of star formation and the triggering of the AGN. [source]

The depolarization properties of powerful radio sources: breaking the radio power versus redshift degeneracy

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2004
J. A. Goodlet
ABSTRACT We define three samples of extragalactic radio sources of Fanaroff,Riley type II, containing 26 objects in total. The control sample consists of 6C and 7C sources with radio powers of around 1027 W Hz,1 at 151 MHz and redshifts of z, 1. The other samples contain 3CRR sources either with comparable redshifts but radio powers about a decade larger or with comparable radio powers but redshifts around z, 0.4. We use these samples to investigate the possible evolution of their depolarization and rotation measure properties with redshift and radio power independently. We used VLA data for all sources at ,4800 MHz and two frequencies within the 1400-MHz band, either from our own observations or from the archive. We present maps of the total intensity flux, polarized flux, depolarization, spectral index, rotation measure and magnetic field direction where not previously published. Radio cores were detected in 12 of the 26 radio sources. Of the sources, 14 show a strong Laing,Garrington effect, but almost all of the sources show some depolarization asymmetry. All sources show evidence for an external Faraday screen being responsible for the observed depolarization. We find that sources at higher redshift are more strongly depolarized. Rotation measure shows no trend with either redshift or radio power. However, variations in the rotation measure across individual sources increase with the redshift of the sources but do not depend on their radio power. [source]

The Granada workshop on High Redshift Radio Galaxies: An overview

ASTRONOMISCHE NACHRICHTEN, Issue 2-3 2006
H. J. A. Röttgering
Abstract The Granada workshop on High Redshift Radio Galaxies (HzRGs) gave an excellent overview of the progress that has been made in this field during the last 3 years. Here we briefly review some of the results, with an emphasis on what studies of HzRGs can teach us about the formation and evolution of massive galaxies, clusters and active galactic nuclei (AGN). Of great relevance for this workshop are scenarios that describe certain aspects of the evolution of radio galaxies, including (i) the sequence of events after merging of galaxies that ultimately lead to extended powerful radio sources and (ii) the mass assembly and virialization of the hosting massive galaxies and their associated (proto-)clusters. Furthermore, I briefly discuss two projects that are important for a further understanding of AGN and high redshift radio galaxies. First, using the MIDI instrument mounted on the VLT Interferometer, the dusty tori of nearby AGN can be studied in the range of 8,13 micron at high angular resolution. The first result on the nearby AGN NGC 1068 as presented by Jaffe et al. (2004) indicated the presence of a hot (T > 800 K), compact (,1 pc) component, possible identified with the base of the jet and a warm (270 K), well-resolved (3 × 4 pc) component associated with the alleged torus. Second, LOFAR is a new low frequency radio telescope that is currently being build in the Netherlands and is expected to be operational in 2008. With 50 stations spread over an area of 100 km in diameter, its resolution and sensitivity will be unprecedented in the frequency range 10,240 MHz. LOFAR will be a unique instrument that will impact a broad range of astrophysical topics varying from the epoch of reionisation, to gamma ray bursts and cosmic rays. Surveys with LOFAR will be of paramount importance for studies of HzRGs: It will enable (i) defining samples of radio galaxies with redshifts higher than 6, (ii) observations of starbursting galaxies in proto-clusters, and (iii) mapping out the low-frequency radio emission of virtually all northern radio-loud AGN in revolutionary detail. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Masses of distant radio galaxies: A coherent view for evolution and origin

ASTRONOMISCHE NACHRICHTEN, Issue 2-3 2006
B. Rocca-VolmerangeArticle first published online: 3 FEB 200
Abstract We hereafter aim to present mass estimates and main parameters of distant powerful radio sources, respectively for evolved stars, ionized gas, and dust. Observations and models are consistent with a scenario where large masses are accumulated whithin extremely short time scales < 1 Gyr at redshifts z > 2: a strong constraint for large-scale structure models. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]