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Session 12 - Radio Galaxies, VLBI.
Display session, Monday, January 15
North Banquet Hall, Convention Center
We present VLA maps and optical identifications from our survey of a sample of 50 objects selected from the MIT-Green Bank (MG) and Parkes-MIT-NRAO (PMN) radio source catalogs, with S_4.85 GHz > 80 mJy. 85% of our subset belong to a class which is not yet well understood or characterized: the ``close'' double-lobed radio galaxies, taken here to have angular sizes in the range 0.''25 < \theta < 2.''0. The rest of the objects either consists of candidate gravitational lens systems, or objects with multiple structure as seen in VLA 8.4 GHz snapshots. All of these objects have moderate to steep spectral indices (\alpha \geq 0.6 for S_\nu \propto \nu^-\alpha). Using optical observations at MDM Observatory, we find an identification rate of atleast 70% for the close doubles to a R_lim \sim 23.5, with a median magnitude of R \sim 19.2 ( 17 < R < 23.5). These objects are also found to be excess in red with most of them in the color range 0 < R-I < 3.5.
Initial analysis of the close double sample suggest that the spectral index is highly correlated with the optical magnitude, and that the identification fraction decreases with increasing spectral index. We also find no evidence for alignment between the radio and optical axes, and have not found strong emission lines in a subsample for which we obtained spectroscopy. Physically close doubles may represent (a) cosmologically distant (high-redshift) radio galaxies, (b) normal doubles but seen from a direction close to the jet axis, (c) relatively young class of sources, having just started to push out their jets, (d) class of sources with growth of the jets been ``frustrated'' by a dense IGM, or (e) 2 images of a gravitationally lensed background source. These and other possibilities to link radio doubles from milli-arcsecond to arc-minute scales will be discussed.
We also present optical identifications and maps for 2 MG and 3 PMN gravitational lens candidates, including MG0248, which is very likely to be a new ``Einstein Ring.''
