  The prominent broad Fe II emission blends in the spectra of active galactic
nuclei have been shown to vary in response to continuum variations, but past
attempts to measure the reverberation lag time of the optical Fe II lines have
met with only limited success. Here we report the detection of Fe II
reverberation in two Seyfert 1 galaxies, NGC 4593 and Mrk 1511, based on data
from a program carried out at Lick Observatory in Spring 2011. Light curves for
emission lines including H-beta and Fe II were measured by applying a fitting
routine to decompose the spectra into several continuum and emission-line
components, and we use cross-correlation techniques to determine the
reverberation lags of the emission lines relative to V-band light curves. In
both cases the measured lag (t_cen) of Fe II is longer than that of H-beta,
although the inferred lags are somewhat sensitive to the choice of Fe II
template used in the fit. For spectral decompositions done using the Fe II
template of Veron-Cetty et al. (2004), we find t_cen(Fe II)/t_cen(H-beta) =
1.9+-0.6 in NGC 4593 and 1.5+-0.3 in Mrk 1511. The detection of highly
correlated variations between Fe II and continuum emission demonstrates that
the Fe II emission in these galaxies originates in photoionized gas, located
predominantly in the outer portion of the broad-line region.
