The Stellar Contents of Intermediate Mass Disk Galaxies in the Virgo Cluster. I. GMOS Spectra

Abstract: The stellar contents of six intermediate mass early-type disk galaxies in the Virgo cluster are examined using deep long slit spectra. The isophotal and photometric properties of the galaxies at near- and mid-infrared wavelengths are also examined. Characteristic ages and metallicities are found by making comparisons with the strengths of lines measured from model spectra. The light from the central regions of these galaxies at visible/red wavelengths is not dominated by old populations. Rather, the central regions of four galaxies (NGC 4305, NGC 4306, NGC 4497, and NGC 4620) are dominated by populations with ages ~ 1.5 - 3 Gyr. Centrally-concentrated line emission is found in two of the galaxies (NGC 4491 and NGC 4584), and the relative strengths of Halpha and [SII]6746 are consistent with this emission originating in star-forming regions. The disks of these galaxies are dominated by populations that are at least 1 Gyr older than those near the centers, indicating that the quenching of star formation progressed from large radii inwards, and did not occur over a short timescale.