Low power compact radio galaxies at high angular resolution

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 10 kpc). Fits of continuous injection models reveal break frequencies in the GHz domain, and ages in the range  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.