Multifrequency VLBI observations of PKS 1413+135: A very young radio galaxy

We present high-dynamic range VLBA maps of the radio galaxy/BL Lac object PKS 1413+135 at 3.6, 6, 13, and 18 cm. These observations reveal that PKS 1413+135 possesses complex, two-sided parsec-scale structure, similar to that of other compact symmetric objects (CSOs). Its morphology appears to be that of a miniature wide-angle-tail (WAT) radio source, and its total power is at the upper extreme of that seen in WATs. Comparison of these maps with previous data reveals no evidence for superluminal motion, and supports the hypothesis that the milliarcsecond-scale structure of PKS 1413+135, unlike most BL Lacs and flat radio spectrum quasars, is not a product of relativistic beaming. However, beaming is likely present within the core seen at 3.6 cm, due to its high brightness temperature. These new VLBA maps allow a more precise, but not completely unambiguous, interpretation of the various absorption data, suggesting that the A(v)>30 mag is due to a normal molecular cloud complex in the disk of the optical spiral galaxy at z=0.247, greater than or similar to few kpc away from its nucleus. The absence of scatter broadening of the core source at 1.6 and 2.3 GHz and the lack of multiple images add to the evidence against the hypothesis (originally suggested by Stocke et al.) that PKS 1413+135 is background to the spiral galaxy at z=0.247, in which the AGN appears centered. But if the AGN is within the spiral, the absence of reprocessed radiation (e.g., near-IR dust continuum and emission lines) remains difficult to understand, since the very high extinction is unlikely to cover the entire dust and line emitting regions. Whether within or background to the optical galaxy, PKS 1413+135 is similar to other CSOs in being a young radio source (of age less than or similar to 10(4) yr), with evidence for absorption along our line of sight. (C) 1996 American Astronomical Society.