The dependence of CO content on morphological type and luminosity for spiral galaxies in the Virgo cluster

Abstract

CO observationss 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 3 sigma level-six Sa's, three Sb's, and nine Sc's. For the Sc galaxies we find that the optical luminosity in the central 5 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 COmore » emission as NGC 4254 (Sc). However, the fraction of the galaxy mass in molecular form is a factor of approx.4 smaller in luminous Sa's than Sc's since the early-type galaxies have higher dynamical masses for a given luminosity.« less