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Paper: Steep-Spectrum Sources from the VLA 74 MHz Survey
Volume: 407, The Low-Frequency Radio Universe
Page: 162
Authors: Dwarakanath, K.S.; Kale, R.
Abstract: We have imaged some of the extremely steep-spectrum sources (α < −1.8; Svα) from the Very Large Array (VLA) survey at 74 MHz, at 1300 MHz using the Giant Meterwave RadioTelescope (GMRT) and at 330 MHz using the VLA in its most extended configuration ( ~ 35 km longest baseline). We have produced images of these steep-spectrum sources at 330 and 1300 MHz with a resolution of ~ 10″ and with sensitivities of ~ 2 and 0.2 mJy/beam respectively. Most of these images show double-lobed morphologies with very little evidence for cores and jets. Four of the 10 sources are at a redshift ~ 0.2. The inferred linear extents and magnetic fields are in the range 100 - 400 kpc and 2 . 15μG respectively. Their 1300 MHz radio luminosities are in the range 3 − 15 × 1023 W Hz−1. These radio sources are relics of past AGN activity. Spectral modeling and evolution indicates that the AGNs in these sources have been switched off for periods in the range 15 - 250 million years. When the AGN was active in radio their radio luminosities would have been ~ 1027 W Hz−1, brighter than the brightest of the known radio galaxies. Since the sources reported here are close to the detection limits of the VLA surveys at 74 and 1400 MHz, it is likely that a large number of such sources remain to be unearthed from more sensitive low-frequency surveys. This population of fossil radio galaxies will have important implications to their understanding and evolution.
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