Issue |
A&A
Volume 436, Number 2, June III 2005
|
|
---|---|---|
Page(s) | 457 - 464 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20052682 | |
Published online | 30 May 2005 |
Optical and radio observations of a sample of 52 powerful ultra-steep spectrum radio sources
1
National Centre for Radio Astrophysics, TIFR, Post Bag 3, Ganesh Khind, Pune 411 007, India e-mail: krishna@ncra.tifr.res.in; kulkarni@ncra.tifr.res.in
2
European Southern Observatory, Alonso de Córdova 3107, Casilla 19001, Vitacura, Santiago, Chile e-mail: cledoux@eso.org; jmelnick@eso.org
3
GAM, Univ. Montpellier II, Place E. Bataillon, 34095 Montpellier Cedex, France e-mail: edmond.giraud@gamum2.in2p3.fr
4
European Space Agency, Villafranca del Castillo, Apartado 50727, 28080 Madrid, Spain e-mail: baltieri@xmm.vilspa.esa.es
Received:
12
January
2005
Accepted:
22
February
2005
We present the results of radio (VLA) and optical (ESO/La Silla) imaging of
a sample of 52 radio sources having an ultra-steep radio spectrum with α
mostly steeper than -1.1 at decimetre wavelengths (median ).
Radio-optical overlays are presented to an astrometric accuracy of
~
. For 41 of the sources, radio spectral indices are newly
determined using unpublished observations made with the 100-m Effelsberg
radio telescope. For 14 of the sources identified with relatively
brighter optical counterparts, spectroscopic observations were also carried
out at La Silla and their redshifts are found to lie in the range 0.4 to 2.6. These observations have revealed three distant clusters of galaxies
with redshifts of 0.55, 0.75 and 0.79, and we suggest that, together with an
ultra-steep radio spectrum and relaxed radio morphology, the presence of a
LINER spectrum in the optical can be used as a powerful indicator of rich
clusters of galaxies. Additional candidates of this type in our sample are
pointed out. Also, sources exhibiting particularly
interesting radio-optical morphological relationships are highlighted. We
further note the presence of six sources in our sample for which the optical
counterpart (either detected or undetected) is fainter than
and the
radio extent is small (<
). These ultra-steep spectrum radio sources
are good signposts for discovering massive galaxies out to very
large redshifts.
Key words: cosmology: observations / galaxies: active / cooling flows / galaxies: clusters: general / quasars: general / radio continuum: galaxies
© ESO, 2005
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