Title:	Relics of double radio sources
Authors:	Dwarakanath, K.S. Kale, Ruta
Keywords:	galaxies: active galaxies: halos galaxies: high-redshift radiation mechanisms: non-thermal radio continuum: galaxies
Issue Date:	20-Jun-2009
Publisher:	IOP Publishing Ltd.
Citation:	Astrophysical Journal, 2009, Vol. 698, pL163
Abstract:	We have formed a new sample which consists of extended extragalactic radio sources without obvious active galactic nuclei (AGNs) in them. Most of these sources appear to be dead double radio sources. These sources with steep spectra (α < –1.8; S vprop να) were identified using the 74 (VLSS) and the 1400 MHz (NVSS) surveys and further imaged using the Very Large Array (VLA) and the Giant Meterwave Radio Telescope (GMRT). The radio morphologies of these sources are rather unusual in the sense that no obvious cores and jets are detected in these sources, but two extended lobes are detected in most. The mean redshift of 4 of the 10 sources reported here is ~ 0.2. At a redshift of 0.2, the linear extents of the sources in the current sample are ~ 250 kpc with their spectral luminosities at 1.4 GHz in the range 2-25 ×1023 W Hz–1. The steep spectra of these sources are a result of the cessation of AGN activities in them about 15-100 million years ago. Before the cessation of AGN activity, the radio luminosities of these galaxies were ~ 1000 times brighter than their current luminosities and would have been comparable to those of the brightest active radio galaxies detected in the local universe (L 1.4 ~ 1027 W Hz–1). The dead radio galaxies reported here represent the "tip of the iceberg" and quantifying the abundance of such a population has important implications to the life cycle of the AGN.
Description:	Restricted Access. An open-access version is available at arXiv.org (one of the alternative locations). Articles older than 2 years are open to all at the journal site (alternative location)
URI:	http://hdl.handle.net/2289/3815
ISSN:	0004-637X 1538-4357 (online)
Alternative Location:	http://adsabs.harvard.edu/abs/2009ApJ...698L.163D http://arxiv.org/abs/0906.0223 http://dx.doi.org/10.1088/0004-637X/698/2/L163
Copyright:	2009 The American Astronomical Society
Appears in Collections:	Research Papers (A&A)

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