Low-frequency study of two giant radio galaxies: 3C 35 and 3C 223

¹ Institute of Astro- and Particle Physics, University of Innsbruck, Technikerstrasse 25/8, 6020 Innsbruck, Austria e-mail: e.orru@astro.ru.nl
² Radboud University Nijmegen, Heijendaalseweg 135, 6525 AJ Nijmegen, The Netherlands
³ INAF – Osservatorio Astronomico di Cagliari, Loc. Poggio dei Pini, Strada 54, 09012 Capoterra (CA), Italy
⁴ INAF – Istituto di Radioastronomia, via Gobetti 101, 40129 Bologna, Italy
⁵ Dipartimento di Astronomia Università degli Studi di Bologna, via Ranzani 1, 40127 Bologna, Italy
⁶ Naval Research Laboratory, Code 7213, Washington DC 20375-5320, USA

Received: 9 December 2009
Accepted: 26 February 2010

Abstract

Aims. Radio galaxies with a projected linear size 1 Mpc are classified as giant radio sources. According to the current interpretation these are old sources which have evolved in a low-density ambient medium. Because radiative losses are negligible at low frequency, extending spectral aging studies in this frequency range will allow us to determine the zero-age electron spectrum injected and then to improve the estimate of the synchrotron age of the source.

Methods. We present Very Large Array images at 74 MHz and 327 MHz of two giant radio sources: 3C 35 and 3C 223. We performed a spectral study using 74, 327, 608 and 1400 GHz images. The spectral shape is estimated in different positions along the source.

Results. The radio spectrum follows a power-law in the hotspots, while in the inner region of the lobe the shape of the spectrum shows a curvature at high frequencies. This steepening agrees with synchrotron aging of the emitting relativistic electrons. In order to estimate the synchrotron age of the sources, the spectra were fitted with a synchrotron model of emission. They show that 3C 35 is an old source of 143 ± 20 Myr, while 3C 223 is a younger source of 72 ± 4 Myr.