The dependence of CO content on morphological type and luminosity forspiral galaxies in the Virgo cluster.
CO observations of the centers of 25 spiral galaxies in the Virgo cluster have been made using the 14 m telescope of the FCRAO (HPBW = 50"). This galaxy sample includes eight Sa, seven Sb, and 10 Sc galaxies, covering a wide range in total luminosity within each morphological class. Eighteen of these galaxies were detected at greater than the 3σ level- six Sa's, three Sb's, and nine Sc's. For the Sc galaxies we find that the optical luminosity in the central S kpc diameter is proportional to the first power of the CO luminosity in the same region, confirming the relation found previously by us for Sc galaxies in the field. For the early-type galaxies (Sa, Sab, Sb) the relation between CO and blue light is slightly displaced from that for the late-type galaxies (Sbc, Sc, Scd) in the sense that for a given CO content the early-type galaxies are more luminous. This trend may be due to the presence of old stars in the nuclear bulge which contribute significantly to the blue light in the early type galaxies. The maximum CO content observed is similar for the early- and late-type galaxies; NGC 4569 (Sab) has as much CO emission as NGC 4254 (Sc). However, the fraction of the galaxy mass in molecular form is a factor of ∼ 4 smaller in luminous Sa's than Sc's since the early-type galaxies have higher dynamical masses for a given luminosity. Because multiaperture photometry data were not available for all of the galaxies in our sample, we have also compared the central CO content with the total B luminosity for the Virgo objects. Both the early and late morphological types show a strong correlation between the CO luminosity in the central 5 kpc diameter and the total B luminosity of the galaxy, such that the galaxies with the highest central CO contents have the highest optical luminosities. Since higher luminosity galaxies have higher masses at every radius than lowluminosity galaxies, this correlation indicates that more molecular clouds are present in the centers of galaxies which have higher total mass densities within each morphological type.