Low power compact radio galaxies at high angular resolution

Free access article

Issue		A&A Volume 441, Number 1, October I 2005


Page(s)		89 - 101
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20053347

A&A 441, 89-101 (2005)
DOI: 10.1051/0004-6361:20053347

Low power compact radio galaxies at high angular resolution

M. Giroletti^{1, 2}, G. Giovannini^{1, 2} and G. B. Taylor^{3, 4}

¹ Dipartimento di Astronomia, Università di Bologna, via Ranzani 1, 40127 Bologna, Italy
e-mail: [giroletti;ggiovann]@ira.cnr.it
² Istituto di Radioastronomia, via Gobetti 101, 40129, Bologna, Italy
³ Kavli Institute of Particle Astrophysics and Cosmology, Menlo Park, CA 94025, USA
e-mail: gtaylor@nrao.edu
⁴ National Radio Astronomy Observatory, PO Box O, Socorro, NM 87801, USA

(Received 2 May 2005 / Accepted 15 June 2005)

Abstract
We present sub-arcsecond resolution multi-frequency (8 and 22 GHz) VLA images of five low power compact (LPC) radio sources, and phase referenced VLBA images at 1.6 GHz of their nuclear regions. At the VLA resolution we resolve the structure and identify component positions and flux densities. The phase referenced VLBA data at 1.6 GHz reveals flat-spectrum, compact cores (down to a few milliJansky) in four of the five sources. The absolute astrometry provided by the phase referencing allows us to identify the center of activity on the VLA images. Moreover, these data reveal rich structures, including two-sided jets and secondary components. On the basis of the arcsecond scale structures and of the nuclear properties, we rule out the presence of strong relativistic effects in our LPCs, which must be intrinsically small (deprojected linear sizes $\la$ 10 kpc). Fits of continuous injection models reveal break frequencies in the GHz domain, and ages in the range $10^{\,5}{-}10^7$ yrs. In LPCs, the outermost edge may be advancing more slowly than in more powerful sources or could even be stationary; some LPCs might also have ceased their activity. In general, the properties of LPCs can be related to a number of reasons, including, but not limited to: youth, frustration, low kinematic power jets, and short-lived activity in the radio.

Key words: radio continuum: galaxies -- galaxies: individual: 1855+37 -- galaxies: active -- galaxies: jets

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