In this paper we analyze the relation between radio, optical continuum and Ha +[N ii] emission from the cores of a sample of 21 nearby Fanaroff and Riley type I galaxies as observed with the VLBA and HST. The emission arises inside the inner tens of parsecs of the galaxies. Core radio emission is observed in 19/20 galaxies, optical core continuum emission is detected in 12/21 galaxies and Ha+[N ii] core emission is detected in 20/21 galaxies. We confirm the recently detected linear correlation between radio and optical core emission in FR I galaxies and show that both core emissions also correlate with central Ha+[N ii] emission. The tight correlations between radio, optical, and Ha+[N ii] core emission constrain the bulk Lorentz factor to y~ 2–5 and y <~ 2 for a continuous jet and a jet consisting of discrete blobs, respectively, assuming jet-viewing angles in the range 30° –90° . Radio and optical core emissions are likely to be synchrotron radiation from the inner jet, possibly with a significant contribution from emission by an accretion disk and/or flow. Elliptical galaxies with LINER nuclei without large-scale radio jets seem to follow the core emission correlations found in FR I galaxies. This suggests that the central engines could be very similar for the two classes of active galactic nuclei (Refer to PDF file for exact formulas).
Department, Program, or Center
School of Physics and Astronomy (COS)
Astronomical Journal 123 (2002) 1334-1356
RIT – Main Campus