EDP Sciences
Free access
Volume 428, Number 3, December IV 2004
Page(s) 847 - 866
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20040423

A&A 428, 847-866 (2004)
DOI: 10.1051/0004-6361:20040423

Absolute kinematics of radio source components in the complete S5 polar cap sample

II. First and second epoch maps at 15 GHz
M. A. Pérez-Torres1, 2, J. M. Marcaide3, J. C. Guirado3 and E. Ros4

1  Istituto di Radioastronomia, via P. Gobetti 101, 40129 Bologna, Italy
    e-mail: torres@iaa.es
2  Instituto de Astrofísica de Andalucía (CSIC), Apdo. Correos 3004, 18080 Granada, Spain
3  Departament d'Astronomia i Astrofísica, Universitat de València, 46100 Burjassot, València, Spain
4  Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany

(Received 11 March 2004 / Accepted 27 July 2004 )

We observed the thirteen extragalactic radio sources of the complete S5 polar cap sample at 15.4 GHz with the Very Long Baseline Array, on 27 July 1999 (1999.57) and 15 June 2000 (2000.46). We present the maps from those two epochs, along with maps obtained from observations of the 2 cm VLBA survey for some of the sources of the sample, making a total of 40 maps. We discuss the apparent morphological changes displayed by the radio sources between the observing epochs. Our VLBA observations correspond to the first two epochs at 15.4 GHz of a program to study the absolute kinematics of the radio source components of the members of the sample, by means of phase delay astrometry at 8.4 GHz, 15.4 GHz, and 43 GHz.

Our 15.4 GHz VLBA imaging allowed us to disentangle the inner milliarcsecond structure of some of the sources, thus resolving components that appeared blended at 8.4 GHz. For most of the sources, we identified the brightest feature in each radio source with the core. These identifications are supported by the spectral index estimates for those brightest features, which are in general flat, or even inverted. Most of the sources display core-dominance in the overall emission, as given by the core-to-extended ratio in the 15.4 GHz frame, Q. We find that three of the sources have their most inverted spectrum component shifted with respect to the origin in the map, which approximately coincides with the peak-of-brightness at both 15.4 GHz and 8.4 GHz.

Key words: astrometry -- techniques: interferometric -- galaxies: quasars: general -- galaxies: BL Lacertae objects: general -- radio continuum: general

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