Evidence for a Population of Short-Lived Powerful Radio \\Galaxies

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Session 53 -- AGN and Radio Galaxies I
Oral presentation, Wednesday, 10:30-12:00, Zellerbach Auditorium Room

[53.07] Evidence for a Population of Short-Lived Powerful Radio \\Galaxies

A.C.S. Readhead, W. Xu, T.J. Pearson (Caltech), P.N. Wilkinson, A. Polatidis (NRAL, Jodrell Bank)

It has recently become clear that the unusual ``compact triple'' radio galaxy 0710+439, discovered almost a decade ago (Readhead, Pearson \& Unwin 1984, IAU Symp.~110, 131), is the prototype member of a distinct class of active galaxies (Conway et al.~1992, ApJ, 396, 62) that we call ``Compact Symmetric'' or CS objects. The distinguishing features of this class are: (1) the radio structure is symmetrically distributed about the center of activity; (2) the overall extent of the radio structure is typically a few hundred parsecs; (3) the radio emission is not strongly beamed; (4) the high-frequency radio spectra are steep; (5) the objects have low polarization; and (6) the objects display weak variability. The symmetry observed in these objects contrasts strongly with the asymmetric nuclear structure observed in most radio-loud objects, be they core-dominated flat-spectrum quasars, lobe-dominated steep-spectrum quasars, lobe-dominated steep-spectrum galaxies, or the majority of steep-spectrum compact objects.

Possible explanations for CS objects include: (1) they are precursors of FR-II objects, (2) they are ``frustrated jets,'' or (3) they are young objects (1000--10,000~yr).

We analyze multifrequency observations of the CS object 2352+495, identified with a galaxy at a redshift of 0.518, and show that the radio activity in this object is almost certainly short-lived - i.e., this is a ``young'' radio object. We use this result, in combination with our observations of two complete samples, to demonstrate that the most plausible explanation is that the CS objects are a previously unsuspected class of short-lived, powerful radio galaxies.

Wednesday program listing