Subrelativistic radio jets and parsec-scale absorption in two Seyfert galaxies

The Very Long Baseline Array has been used at 15 GHz to image the milliarcs econd structure of the Seyfert galaxies Mrk 231 and Mrk 348 at two epochs s eparated by about 1.7 yr. Both galaxies contain parsec-scale double radio s ources whose components have brightness temperatures of 10(9)-10(11) K, imp lying that they are generated by synchrotron emission. The nuclear componen ts are identified by their strong variability between epochs, indicating th at the double sources represent apparently one-sided jets. Relative compone nt speeds are measured to be similar to 0.1c at separations of 1.1 pc or le ss (for H-0 = 65 km s(-1) Mpc(-1)), implying that parsec-scale Seyfert jets are intrinsically different from those in most powerful radio galaxies and quasars. The lack of observed counterjets is most likely due to free-free absorption by torus gas, with an ionized density n(e) greater than or simil ar to 2 x 10(5) cm(-3) at T approximate to 8000 K, or n(e) greater than or similar to 10(7) cm(-3) at T approximate to 10(6.6) K, in the inner parsec of each galaxy. The lower density is consistent with values found from X-ra y absorption measurements, while the higher temperature and density are con sistent with direct radio imaging of the NGC 1068 torus by Gallimore,Baum, & O'Dea.