FIRST-based survey of Compact Steep Spectrum sources

Free access article

Issue		A&A Volume 440, Number 1, September II 2005


Page(s)		93 - 105
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20042496

A&A 440, 93-105 (2005)
DOI: 10.1051/0004-6361:20042496

II. MERLIN and VLA observations of medium-sized symmetric objects

M. Kunert-Bajraszewska¹, A. Marecki¹, P. Thomasson² and R. E. Spencer²

¹ Torun Centre for Astronomy, N. Copernicus University, 87-100 Torun, Poland
e-mail: amr@astro.uni.torun.pl
² Jodrell Bank Observatory, The University of Manchester, Macclesfield, Cheshire SK11 9DL, UK

(Received 7 December 2004 / Accepted 13 May 2005 )

Abstract
A new sample of candidate Compact Steep Spectrum (CSS) sources that are much weaker than the CSS source prototypes has been selected from the VLA FIRST catalogue. MERLIN "snapshot" observations of the sources at 5 GHz indicate that six of them have an FR II-like morphology, but are not edge-brightened as is normal for Medium-sized Symmetric Objects (MSOs) and FR IIs. Further observations of these six sources with the VLA at 4.9 GHz and MERLIN at 1.7 GHz, as well as subsequent full-track observations with MERLIN at 5 GHz of what appeared to be the two sources of greatest interest are presented. The results are discussed with reference to the established evolutionary model of CSS sources being young but in which not all of them evolve to become old objects with extended radio structures. A lack of stable fuelling in some of them may result in an early transition to a so-called coasting phase so that they fade away instead of growing to become large-scale objects. It is possible that one of the six sources (1542+323) could be labelled as a prematurely "dying" MSO or a "fader".

Key words: radio continuum: galaxies -- galaxies: active -- galaxies: evolution

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