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|A new sample of large angular size radio galaxies. III. Statistics and evolution of the grown population|
We present in this paper a detailed study of a new sample of largeangular size FR I and FR II radio galaxies and compare the properties ofthe two classes. As expected, a pure morphology based distinction of FRIs and FR IIs corresponds to a break in total radio power. The radiocores in FR Is are also weaker than in FR IIs, although there is not awell defined break power. We find that asymmetry in the structure of thesample members must be the consequence of anisotropies in the mediumwhere the lobes expand, with orientation playing a minor role. Moreover,literature data and our observations at kiloparsec scales suggest thatthe large differences between the structures of FR I and FR II radiogalaxies must arise from the poorly known central kiloparsec region oftheir host galaxies. We analyze the sub-sample of giant radio galaxies,and do not find evidence that these large objects require higher corepowers. Our results are consistent with giant radio galaxies being theolder population of normal FR I and FR II objects evolving in lowdensity environments. Comparing results from our sample with predictionsfrom the radio luminosity function we find no evidence of a possible FRII to FR I evolution. Moreover, we conclude that at z 0.1, one outof four FR II radio sources has a linear size above 500 kpc, thus beingin an advanced stage of evolution (for example, older than 10 Myrassuming a jet-head velocity of 0.1c). Radio activity seems to be ashort-lived process in active galaxies, although in some casesrecurrent: five objects in our sample present signs of reactivation intheir radio structures.
|A new sample of large angular size radio galaxies. II. The optical data|
We constructed and presented in the first paper of this series a newsample of 84 large angular size radio galaxies by selecting from theNRAO VLA Sky Survey objects with angular size >=4arcmin , declinationabove +60deg and total flux density at 1.4 GHz >= 100 mJy.In this paper we present optical spectra and images of those galaxiesassociated with the radio emission for which no redshift was known priorto our observations. Optical counterparts have been identified for all(but one) members of the sample. After our observations, a reliablespectroscopic redshift is available for 67 objects (80%) from thesample. This paper, the second of a series of three, contributes toincrease the number of well-defined samples of radio galaxies with amplespectroscopic information.
|A new sample of large angular size radio galaxies. I. The radio data|
We present a new sample of 84 large angular size radio galaxies selectedfrom the NRAO VLA Sky Survey. Radio sources with declination above+60deg, total flux density greater than 100 mJy at 1.4 GHzand angular size larger than 4arcmin have been selected and observedwith the VLA at 1.4 and 4.9 GHz. The radio observations attempt toconfirm the large angular size sources and to isolate the core emissionfor optical identification. In this paper, the first of a series ofthree, we present radio maps of 79 sources from the sample and discussthe effects of the selection criteria in the final sample. 37 radiogalaxies belong to the class of giants, of which 22 are reported in thispaper for the first time. Complete Fig.~2 is only available inelectronic form at http://www.edpsciences.org
|A spectroscopic study of NGC 6251 and its companion galaxies|
Measurements of the velocities of galaxies thought to be associated withthe giant radio galaxy NGC 6251 confirm the presence of a poor clusterwith a systemic redshift of z=0.0244+/-0.0004 and a line-of-sightvelocity dispersion ofσz=283(+109,-52)kms-1. This suggests acluster atmosphere temperature of T=0.7(+0.6,-0.2)keV, which is notenough to confine the radio jet by gas pressure. The core of NGC 6251shows strong emission lines of [Oiii] and Hα+[Nii], but there isno evidence for line emission from the jet (detected in opticalcontinuum by Keel).
|Arcsecond Positions of UGC Galaxies|
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.
|Possible systematic redshifts in a chain of galaxies.|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973ApJ...182..351G&db_key=AST
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