Properties of the molecular interstellar medium in the lenticular galaxy NGC 5866

Abstract

The IRAM 30m telescope has been used to observe the J = 1-0 transition of [superscript 12]CO at several positions along the central dust lane of NGC 5866. The data were used to determine the large-scale properties of the molecular interstellar medium. We find that the interstellar medium mass, M(H[subscript 2]) = 4.55 ± 0.43 × 10 [superscript 8] M[symbol for sun], is consistent with simple mass-return calculations from evolved stars (e.g. Faber & Gallagher, 1976). A computer model was employed to constrain the distribution and kinematics of the gas, by attempting to simulate the multi-position spectroscopy. The gas is found to be in a broken Gaussian ring-like distribution with several warmer areas mostly found on the red shifted side. Rotation velocities much higher than those reported for both the stars and the ionized gas are required to reproduce the observed CO line width. The star formation rate is [approximately equal to]0.05 M[symbol for sun]/yr from Hα data, about average for an S0 galaxy, suggests that NGC 5866 is in mass balance based on the calculated mass return rate. The origin of the gas is most likely internal. However, the rapid rotation of the gas, a M [subscript H2]/M[subscript HI] ≥ 3.5, and evidence for a higher star formation rate in the past suggest that the gas might have been perturbed by an outside influence.