Radio galaxies in VLBI

 
 
 

 
The two-sided parsec-scale emission of the FRII radio galaxy 3C452.
 
Gabriele  Giovannini, Luigina Feretti, Venturi Tiziana, Lucas Lara, Bill Cotton
 

 
    We have been observing a complete sample of radio galaxies of low-intermediate luminosity (Giovannini, Feretti and Comoretto,  1990, ApJ 358 159) at VLBI resolution and in a wide range of  frequencies .
The sample includes low luminosity FRI radio galaxies, powerful FRIIs, intermediate power radio galaxies, compact and core-halo radio sources.
With the present work we wish to address a number of questions. In particular:

   Are low luminosity radio galaxies (FRIs) the unbeamed population of BL Lacertae objects, as suggested by the unified schemes? To test this hypothesis we need parsec-scale maps of FRI radio galaxies, in order to derive estimates of the intrinsic Lorentz factors for the relativistic plasma, and plausible values for the orientation of the radio emission with respect to the line of sight . Expected values from the theory are Lorentz factors greater
than (or equal to) approximately 2 and viewing angles larger than 30 degrees.

If FRI radio galaxies are the parent population of BL Lacertae objects, then we expect relativistic intrinsic speed on the parsec scale. Do they also show proper motion of features, as it is common for powerful radio sources with highly relativistic plasma speed?

Do FRIs and FRIIs radio galaxies differ on the parsec-scale? If so, how? A large fraction of the radio galaxies in the sample have already been observed at parsec-scale resolution at various frequencies, and for some of them multiepoch observations already exist.
 
Which is the relation between the compact radio sources and the extended radio galaxies in the
same power range?
 
 

Most relevant papers published in this research area:
 
 
G. Giovannini, W.D. Cotton, L. Feretti, L. Lara, Venturi T., VLBI Observations of a Complete Sample of Radio Galaxies. 10 Years Later, 2001, ApJ 552, 508

Cotton W.D., Feretti L., Giovannini G., Lara L., Venturi T., A Parsec-Scale Accelerating Jet in the Giant Radio Galaxy NGC315, 1999, ApJ 519, 108

Giovannini G., Cotton W.D., Feretti L., Lara L.,Venturi T., VLBI Observations of a Complete Sample of Radio Galaxies. VIII - Proper Motion in 3C338, 1998, ApJ 493, 632

 Lara L., Cotton W.D., Feretti L., Giovannini G., Marcaide J.M., Venturi T.,  VLBI Observations of a complete sample of radio galaxies. VII., 1997, ApJ, 474, 179

Baum S.., O'Dea C., Giovannini G., Biretta J., Cotton W., de Koff S., Feretti L., Golombek D., Lara L., Macchetto F., Miley G.K., Sparks W.B., Venturi T.,  HST and MERLIN Observations of 3C264 - A Laboratory for Jet Physics and Unified Schemes, 1997 ApJ 483, 178

Feretti L., Giovannini G., Comoretto G., Venturi T., Wehrle A.E., VLBI Observations of a Complete Sample of Radiogalaxies. III-The Two-sided mas Structure of 3C338, 1993, ApJ. 408, 446

Venturi T., Giovannini G., Feretti L., Comoretto G., Wehrle A.E., VLBI Observations of a Complete Sample of Radiogalaxies. II-The Parsec-scale Structure of NGC315, 1993, ApJ. 408, 81

Giovannini G., Feretti L., Venturi T., Lara L., Marcaide J.M., Rioja M.J., Spangler S.R., Wehrle A.E.,  VLBI Observations of a Complete Sample of Radio Galaxies. IV - The Radio Galaxies NGC2484, 3C109, 3C382, 1994, ApJ 435, 116

Venturi T., Castaldini C., Cotton, W.D., Feretti, L., Giovannini, G., Lara, L., Marcaide, J.M., VLBI Observations of a complete sample of radio galaxies. VI. The two FRI radio galaxies B2 0836+29 and 3C465, 1995, ApJ 454, 735

Cotton, W.D., Feretti, L., Giovannini, G., Venturi T., Lara, L., Marcaide, J.M., Wehrle A.E.,  VLBI Observations of a complete sample of radio galaxies. V. 3C346 and 4C31.04: Two Unusual CSS, 1995, ApJ 452, 605
 


 

          tventuri@ira.bo.cnr.it