  In this paper we analyze the relation between radio, optical continuum and
Halpha+[NII] emission from the cores of a sample of 21 nearby Fanaroff & Riley
type I galaxies as observed with the VLBA and HST. The emission arises inside
the inner tens of parsec of the galaxies. Core radio emission is observed in
19/20 galaxies, optical core continuum emission is detected in 12/21 galaxies
and Halpha+[NII] 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
Halpha+[NII] emission. The tight correlations between radio, optical and
Halpha+[NII] core emission constrain the bulk Lorentz factor to gamma ~ 2-5 and
gamma =< 2 for a continuous jet and a jet consisting of discrete blobs,
respectively, assuming jet viewing angles in the range [30deg,90deg]. 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 AGNs.
