TANAMI: tracking active galactic nuclei with austral milliarcsecond interferometry

I. First-epoch 8.4 GHz images

¹ United States Naval Observatory, 3450 Massachusetts Ave., NW, Washington DC 20392, USA e-mail: rojha@usno.navy.mil
² NVI, Inc., 7257D Hanover Parkway, Greenbelt, MD 20770, USA
³ Dr. Remeis Sternwarte, Astron. Institut der Universität Erlangen-Nürnberg, Sternwartstrasse 7, 96049 Bamberg, Germany e-mail: matthias.kadler@sternwarte.uni-erlangen.de
⁴ Erlangen Centre for Astroparticle Physics, Erwin-Rommel Str. 1, 91058 Erlangen, Germany
⁵ CRESST/NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
⁶ Universities Space Research Association, 10211 Wincopin Circle, Suite 500 Columbia, MD 21044, USA
⁷ Hartebeesthoek Radio Astronomy Observatory, PO Box 443, Krugersdorp 1740, South Africa
⁸ The Catholic University of America, 620 Michigan Ave., N.E., Washington, DC 20064, USA
⁹ Australia Telescope National Facility, CSIRO, PO Box 76, Epping, NSW 1710, Australia
¹⁰ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
¹¹ Bundesamt fur Kartographie und Geodesie, Germany entrusted with Transportable Integrated Geodetic Observatory, Universidad de Concepcion, Casilla 4036, Correo 3, Concepcion, Chile
¹² Canberra Deep Space Communication Complex, PO Box 1035, Tuggeranong, ACT 2901, Australia
¹³ Department of Physics, Purdue University, 525 Northwestern Avenue, West Lafayette, IN 47907, USA
¹⁴ School of Mathematics & Physics, Private Bag 37, University of Tasmania, Hobart TAS 7001, Australia
¹⁵ Federal Agency for Cartography and Geodesy (BKG), Geodetic Observatory Wettzell, Sackenrieder Str. 25, 93444 Bad Kötzting, Germany
¹⁶ Dept. d'Astronomia i Astrofísica, Universitat de València, 46100 Burjassot, València, Spain
¹⁷ Department of Physics and Astronomy, University of New Mexico, Albuquerque NM, 87131, USA (Greg Taylor is also an Adjunct Astronomer at the National Radio Astronomy Observatory.)
¹⁸ Astrophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
¹⁹ Curtin Institute of Radio Astronomy, Curtin University of Technology, Bentley, WA, 6102, Australia
²⁰ Istituto Nazionale di Fisica Nucleare, Sezione di Perugia, 06123 Perugia, Italy
²¹ Dipartimento di Fisica, Università degli Studi di Perugia, 06123 Perugia, Italy

Received: 19 June 2009
Accepted: 12 May 2010

Abstract

Context. A number of theoretical models vie to explain the γ-ray emission from active galactic nuclei (AGN). This was a key discovery of EGRET. With its broader energy coverage, higher resolution, wider field of view and greater sensitivity, the Large Area Telescope (LAT) of the Fermi Gamma-ray Space Telescope is dramatically increasing our knowledge of AGN γ-ray emission. However, discriminating between competing theoretical models requires quasi-simultaneous observations across the electromagnetic spectrum. By resolving the powerful parsec-scale relativistic outflows in extragalactic jets and thereby allowing us to measure critical physical properties, Very Long Baseline Interferometry observations are crucial to understanding the physics of extragalactic γ-ray objects.

Aims. We introduce the TANAMI program (Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry) which is monitoring an initial sample of 43 extragalactic jets located south of -30 degrees declination at 8.4 GHz and 22 GHz since 2007. All aspects of the program are discussed. First epoch results at 8.4 GHz are presented along with physical parameters derived therefrom.

Methods. These observations were made during 2007/2008 using the telescopes of the Australian Long Baseline Array in conjunction with Hartebeesthoek in South Africa. These data were correlated at the Swinburne University correlator.

Results. We present first epoch images for 43 sources, some observed for the first time at milliarcsecond resolution. Parameters of these images as well as physical parameters derived from them are also presented and discussed. These and subsequent images from the TANAMI survey are available at http://pulsar.sternwarte.uni-erlangen.de/tanami/.

Conclusions. We obtain reliable, high dynamic range images of the southern hemisphere AGN. All the quasars and BL Lac objects in the sample have a single-sided radio morphology. Galaxies are either double-sided, single-sided or irregular. About 28% of the TANAMI sample has been detected by LAT during its first three months of operations. Initial analysis suggests that when galaxies are excluded, sources detected by LAT have larger opening angles than those not detected by LAT. Brightness temperatures of LAT detections and non-detections seem to have similar distributions. The redshift distributions of the TANAMI sample and sub-samples are similar to those seen for the bright γ-ray AGN seen by LAT and EGRET but none of the sources with a redshift above 1.8 have been detected by LAT.