THE NEAREST GHZ PEAKED-SPECTRUM RADIO GALAXY, PKS-1718-649

In this paper we identify PKS 1718-649, at a distance of 56 Mpc (z=0.0 14; H-0=75 km s(-1) Mpc(-1), q(0)=0), as the nearest GHz peaked-spectr um (GPS) radio galaxy, more than four times closer than any previously known. Extensive observations at radio wavelengths with the Australia Telescope Compact Array, the Southern Hemisphere VLBI Experiment arra y, and the Swedish-ESO Submillimetre Telescope have allowed us to dete rmine the properties of the radio source: PKS 1718-649 consists of two compact sub-pc-scale components separated by approximately 2 pc, the overall radio polarization is low, and the radio spectrum is peaked ne ar 3 GHz. Order-of-magnitude agreement between the quantitative model for GPS sources of Bicknell et al. [ApJ (1997) (in press)] and the rad io data we present, as well as data at optical wavelengths from the li terature, raises the interesting possibility that PKS 1718-649 may be frustrated in its development by the nuclear environment of its host g alaxy, NGC 6328. The model of Bicknell et al. (1997) suggests free-fre e absorption as an explanation of the PKS 1718-649 radio spectrum. How ever, both free-free absorption and synchrotron self-absorption mechan isms are plausible for this source and both may contribute to the over all radio spectrum. PKS 1718-649 provides evidence to strengthen the s peculative suggestion that GPS sources arise as a consequence of galax y merger activity. (C) 1997 American Astronomical Society.