Intermediate-mass Early-type Disk Galaxies in the Virgo Cluster. II.
  Near-Infrared Spectra and Evidence for Differences in Evolution
  We discuss near-infrared (NIR) slit spectra of six early-type disk galaxies
in the Virgo Cluster. While the depth of the CO(2,0) band is consistent with
the centers of these galaxies having solar or slightly sub-solar
luminosity-weighted metallicities, galaxy-to-galaxy variations in the depth of
the NaI 2.21um doublet are found, with NaI2.21um lines in three galaxies (NGC
4491, NGC 4584, and NGC 4620) that are deeper than those predicted for a solar
chemical mixture and a solar-neighborhood mass function. Considering the depth
of the NaD lines found by Davidge (2018a), the deep NaI2.21um lines are
tentatively attributed to a bottom-heavy mass function. This is counter to
observed trends between mass function slope and velocity dispersion. Two of the
three galaxies with deep NaI2.21um (NGC 4584 and NGC 4620) have Sersic
exponents that are consistent with a classical bulge. As for NGC 4491, its
central NIR spectrum contains prominent emission lines. The relative strengths
of Brgamma and H_2S(1), the presence of [FeII] emission, and the mid-infrared
spectral-energy distribution are all consistent with intense recent star
formation near the center of that galaxy. Wavelengths that contain the
Ballick-Ramsey C_2 band at 1.76um are matched by moderately metal-poor E-MILES
model spectra with an age of 2 Gyr. It is concluded that these galaxies have
evolved in a cluster environment for at least several Gyr.
