Journal Article

Deep low-frequency observations with the Giant Metrewave Radio Telescope: a search for relic radio emission

S. K. Sirothia, D. J. Saikia, C. H. Ishwara-Chandra and N. G. Kantharia

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 392, issue 4, pages 1403-1412
Published in print February 2009 | ISSN: 0035-8711
Published online January 2009 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2008.14015.x
Deep low-frequency observations with the Giant Metrewave Radio Telescope: a search for relic radio emission

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We present deep multifrequency observations using the Giant Metrewave Radio Telescope (GMRT) at 153, 244, 610 and 1260 MHz of a field centred on J0916+6348, to search for evidence of fossil radio lobes which could be due to an earlier cycle of episodic activity of the parent galaxy, as well as haloes and relics in clusters of galaxies. We do not find any unambiguous evidence of episodic activity in a list of 374 sources, suggesting that such activity is rare even in relatively deep low-frequency observations. We examine the spectra of all the sources by combining our observations with those from the Westerbork Northern Sky Survey (WENSS), NRAO (National Radio Astronomy Observatories) VLA (Very Large Array) Sky Survey (NVSS) and the Faint Images of the Radio Sky at Twenty-Centimeters Survey (FIRST). Considering only those which have measurements at a minimum of three different frequencies, we find that almost all sources are consistent with a straight spectrum with a median spectral index, α∼ 0.8 [S(ν) ∝ν−α], which appears steeper than theoretical expectations of the injection spectral index. We identify 14 very steep-spectrum sources with α≥ 1.3. We examine their optical fields and discuss the nature of some of these sources.

Keywords: galaxies: active; galaxies: clusters: general; radio continuum: galaxies

Journal Article.  4955 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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