We present an atlas of moderate-resolution (R ~ 1200-1600) optical spectra of
94 low-redshift (z < 0.5) active galactic nuclei taken with the Magellan 6.5 m
Clay Telescope. The spectra mostly cover the rest-frame region 3600-6000 Ang.
All the objects have preexisting Hubble Space Telescope imaging, and they were
chosen as part of an ongoing program to investigate the relationship between
black hole mass and their host galaxy properties. A significant fraction of the
sample has no previous quantitative spectroscopic measurements in the
literature. We perform spectral decomposition of the spectra and present
detailed fits and basic measurements of several commonly used broad and narrow
emission lines, including [O II] 3727, He II 4686, Hbeta, and [O III] 4959,
5007. Eight of the objects are narrow-line sources that were previously
misclassified as broad-line (type 1) Seyfert galaxies; of these, five appear
not to be accretion-powered.Comment: To appear in ApJS, 25 page